Analytical Hierarchy Process applied to maintenance strategy selection for offshore platforms in challenging environments.

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Nnaemeka Nwogbe
S1538433
MSc Mechanical Engineering with Manufacturing.
Glasgow Caledonian University
Analytical Hierarchy Process applied to
maintenance strategy selection for offshore
platforms in challenging environments.

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ABSTRACT
Maintenance policy selection is a very important task for any engineering industry.
An attempt to formulate an effective maintenance management framework in order to
cope with challenges of extreme environment is of significance to the offshore
industry. That being said the offshore industry faces a challenging situation in
maintaining a level of production at isolated and often harsh locations as is common
offshore. Maintenance is of utmost importance not only in order to achieve
prolongation of the life of platforms, but also for environment and for general health
and safety of personnel aboard the not easily accessible oil platforms. The aim of this
research was to integrate the Analytical Hierarchy Process (AHP), to select the most
appropriate maintenance strategy for a challenging environment faced by offshore
platforms. Whilst providing new insight into the capability of the AHP methodology.
This aim has been accomplished utilizing interview response from shell Maintenance
and Inspection supervisors and two case studies based on: Petronas and Analysis of
the failure of an offshore compressor crankshaft.
As a result from this research, the maintenance strategy based on information
obtained was produced using the AHP multi criteria decision weighing methodology
as implemented on a compressor in a corrosive environment.

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ACKNOWLEDGEMENTS
Ending a four-month journey of research, but also personal growth, there are some
reflections to be made. I would like to thank my supervisor Dr. Babakalli, for his
support and advice through this trying time. I would also like to thank the
maintenance and Inspection supervisors that took part in the interview, my brother
Nnadozie Nwogbe for setting it all up and for all his support, my brother Obinna
Nwogbe for keeping an eye on my progress and making sure I was on track, my
parents for all their love and support.

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CONTENTS
CHAPTER 1............................................................................................................................................................6
INTRODUCTION ANDPOSITIONING..........................................................................................................6
1.1. Background..............................................................................................................................................6
1.1. Shell............................................................................................................................................................9
1.2. Problem Statement and Scope......................................................................................................10
1.3. Aim and objectives..............................................................................................................................11
1.4. Research questions. .........................................................................................................................11
1.5. Delimitations.......................................................................................................................................12
1.6. Structure of paper...............................................................................................................................12
CHAPTER 2..........................................................................................................................................................14
LITERATURE REVIEW....................................................................................................................................14
2.1. Challenges met in an offshore environment. .........................................................................14
2.2. Selecting a maintenance approach using AHP multiple criteria decision-making.
..............................................................................................................................................................................17
2.3. Maintenance strategy utilized on an offshore oil platform...............................................18
CHAPTER 3..........................................................................................................................................................24
OVERVIEW...........................................................................................................................................................24
3. Oil and Gas Industry ...................................................................................................................................24
3.1. Offshore Industry..........................................................................................................................25
3.1.1. Offshore Exploration and Planning...........................................................................26
3.1.2. Offshore Production...........................................................................................................28
3.2. Offshore platforms..............................................................................................................................30
3.3.1. Platform Type and Design...........................................................................................30
3.4. Critical equipment in the Oil and Gas Industry.....................................................................36
3.4.1. Safety Critical.........................................................................................................................36
3.4.2. Safety critical equipment...............................................................................................38
3.4.3. Operation Critical................................................................................................................47
CHAPTER 4..........................................................................................................................................................50
RESEARCH METHODOLOGY........................................................................................................................50
4. Research Overview....................................................................................................................................50
4.1. Research Approach. .....................................................................................................................50

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4.2. Research Process.................................................................................................................................51
4.2.1. Delphi Interview Technique..........................................................................................52
4.2.2. Case study............................................................................................................................55
4.3. Validity.....................................................................................................................................................56
4.4. Findings.............................................................................................................................................56
4.5. Corrosion..........................................................................................................................................56
4.5.1. Environmental influences.............................................................................................57
4.5.2. Contribution of process and equipment conditions.....................................58
4.6. Corrosion Maintenance..................................................................................................................60
4.6.1. Corrosion maintenance tasks......................................................................................61
4.7. Corrosion maintenance strategy. ................................................................................................62
4.7.1. Corrective Maintenance.................................................................................................62
4.7.2. Preventative Maintenance............................................................................................63
4.7.3. Predictive Maintenance or Condition-Based Maintenance.......................63
4.7.4. Reliability-Centered Maintenance...........................................................................64
4.8. Compressor............................................................................................................................................64
4.9. Analytical Hierarchy Process (AHP)..........................................................................................65
Chapter 5 ..............................................................................................................................................................71
DATA ANALYSIS................................................................................................................................................71
5. Application of the Analytical Hierarchy Process...........................................................................71
CHAPTER 6..........................................................................................................................................................80
DISCUSSION & CONCLUSIONS....................................................................................................................80
6.1. Discussion.........................................................................................................................................80
6.2. Conclusion........................................................................................................................................81
6.3. Future Research Work..................................................................................................................83
6.3.1. Analytical Network Process (ANP)............................................................................84
6.3.2. Fuzzy AHP.................................................................................................................................84
REFERENCE.........................................................................................................................................................85
APPENDIX............................................................................................................................................................97
Appendix A......................................................................................................................................................97
Appendix B......................................................................................................................................................98
Appendix C......................................................................................................................................................99
Appendix D ..................................................................................................................................................103
Appendix E...................................................................................................................................................105

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CHAPTER 1
INTRODUCTION AND POSITIONING.
This chapter is intended to give the reader an insight and understanding into the aim,
objective and expected results of the dissertation. This is accomplished by explaining
the relevance of the topic to the industry, academia and in most cases the economy.
1.1. Background.
To appreciate the purpose of this dissertation it is vital to understand the role of the oil
and gas industry. According to Kendrick Oil Company (2015), oil provides one-third
of the world’s energy supply and the addition of natural gas, increases that to over 50
percent. Both of the world’s alternative energy sources; wind and solar power, cannot
compare in production to that of petroleum. In 2010, petroleum production was over
5,700 gigawatts compared to 24 gigawatts of wind and 3.4 gigawatts of solar power
produced the same year. What this implies is that without ongoing production of what
is recognized as the dominant source of energy in today’s society. The result would be
an economical downfall.
That being said, the management of maintenance operations in the oil and gas
industry is of severe importance to both its effectiveness and efficiency. The oil and
gas industry is one recognized for its expensive specialized equipment and strict
environmental considerations. The industry is often antagonized with ever changing
rules and regulations. Answerable to a number of regulatory bodies, that deal with

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environmental impact as well as health and safety. Irrespective of the efforts made by
many companies to put in place an effective maintenance and safety culture, an
incident occurs that often involves a massive loss of life and property and leaves
many devastated and fearful of the possibility that it may happen again.
The consequence of poor maintenance practice stems even further; Steve Sonnenberg,
president of Emerson Process Management states, “Chief executives are seeing the
need to better manage physical assets for improved profitability.” He goes on to
explain that “With the right strategy, the typical $1 billion USD plant can save $12
million or more annually in maintenance costs – not including the corresponding
operational and production benefits from reduced downtime.”
Boschee (2013) compares the US industrial average downtime, which ranges from
3% to 5%, with that of oil and gas industry’s, which have an estimated downtime
ranging from 5% to 10%. This indicates a need for improvement in reliability and
maintenance of facilities, equipment, and processes. Robert MacArthur, head of ABS
Group’s asset and maintenance optimization practice, states, “I have been on offshore
platforms that were in a crisis mode of operation, running at 30% unplanned
downtime.” He goes on to estimate that the oil and gas industry may also fail to meet
high standards for another key performance indicator (KPI) – assets meeting their
engineered life expectancy. He explains that the “Midstream and Downstream asset
life expectancy is about 65%, but offshore is estimated to be somewhat lower,” This
begs the question, why is there a significant result of poor maintenance in the offshore
industry?
The Offshore industry is a large and diverse sector that has seen rapid growth since
the very first platform was installed in 1947. These developments are evident
particularly in the exploration and development of offshore oil and gas fields in deep
waters. According to the international Energy Agency around 30% of the 85 million
barrels per day of oil consumed are sourced from offshore oil wells with a tendency to
increase. The offshore output has more significance for those outside the organization
of the petroleum exporting countries causing them to rely primarily on production.

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The industry faces a challenging situation in maintaining a level of production at
isolated and often harsh locations as is common offshore. Maintenance is of utmost
importance not only in order to achieve prolongation of the life of platforms, but also
for environment and for general health and safety of personnel aboard the not easily
accessible oil platforms. According to Lo (2016), there has been a major decline in
production efficiency and lost revenues. He makes reference to a 2014 report
published by consulting firm Mckinsey & Company and cited data from the UK
Department of Energy and Climate Change, that states that the production efficiency
on the UK Continental Shelf (UKCS) had declined from 81% in 2004 to 60% in 2012.
It can be understood that the challenging conditions in certain offshore sites directly
affect the maintenance strategy implemented at those sites. Craig Wiggins, head of
UK maintenance, modifications and operations for oilfield services company Aker
solutions explains that the weather conditions on offshore sites can be very difficult.
“Poor weather often disrupts travel and causes logistical challenges as well as
increasing HSE risks.” These harsh weather conditions often affect the equipment of
offshore platforms causing a reduction in reliability and increasing the frequency of
required maintenance. (Maybe add some more on equipment)
Maintenance policy selection is a very important task for any engineering industry.
An attempt to formulate an effective maintenance management framework in order to
cope with challenges of extreme environment is of significance to the offshore
industry. An improper selection can have a detrimental effect on a company due to an
increased operating budget and unplanned maintenance costs. For this purpose it is
rather important to consider a number of criteria such as safety, cost, added value,
mean time between failures (MTBF), and mean time to repair (MTTR). When
reviewing maintenance procedures, management is typically asked to select the best
maintenance policy for each piece of equipment or system from a set of alternatives.
For example, corrective, preventative, opportunistic, condition based, predictive
maintenance, etc. This selection process is dependent on a number of criteria; the
decision will affect the allocation of resource, technology selection, management and
organization process, etc. Therefore, In order to select a suitable strategy, it is
necessary to make a decision based on facts. Decision-making process and judgment

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regarding selection of maintenance strategy are often discontinuous, complex and
unstructured (Hajshirmohammadi and Wedley, 2004). To solve this problem several
decision approaches have been developed. Almeida and Bohoris (1995) deliberate the
use of a decision making theory to maintenance, paying close attention to multiple
utility theory. Triantaphaphyllou et al. (1997) suggests using an analytical hierarchy
process that takes into consideration only four maintenance criteria: cost, reparability,
reliability and availability. The Reliability Centered Maintenance is a widely utilized
maintenance policy selection that has had much success in the offshore industry.
Rausand and Vatn (2008) suggest that a major advantage of the RCM analysis process
is a structured, and traceable approach to determine the optimal type of preventative
maintenance (PM). Achieved through a detailed analysis of failure modes and failure
causes. Bevilacqua and Braglia (2000) presented an application of the Analytical
Hierarchy Process (AHP) for maintenance strategy selection in an Italian oil refinery
processing plant, combining many features which are important in the selection of the
maintenance policy: economic factors, applicability and costs, safety, etc. Using this
approach, the selection of a maintenance policy can be accomplished by combining
qualitative and quantitative considerations in a systematic framework.
1.1. Shell
Shell is an Anglo-Dutch multinational oil and gas Company, with its headquarters in
the Netherlands and integrated in the United Kingdom. It is recognized as the seventh
largest company in the world, in terms of revenue as of 2016. As of 2013, shell’s
revenue was equal to 85.4% of the Netherlands $555.8 billion GDP; furthermore
they’re one of the world most valuable companies. With operations in over 90
countries, producing around 3.1 million barrels of oil equivalent per day and have
44,000 service stations worldwide.

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1.2. Problem Statement and Scope.
Based on the information supplied in the background, it is clear that an optimal
maintenance strategy is required. However, there is limited research on the
effect extreme environments have on the maintenance strategy in the offshore
oil and gas industry. In offshore oil production preventative maintenance is
recognized as one of the major activities in maintaining the highest output of oil
produced at a low cost. The challenge in the offshore industry is the appropriate
preventative maintenance/inspection intervals of offshore platforms, and even
more so platforms in extreme conditions. The offshore industry recognized that
the predicted structure loads and its effect as well as the resistance of a platform
would be subject to uncertainties. The harsh environment creates the need for a
specialized logistic and maintenance strategy capable of overcoming the
difficulties. Factors such as, corrosive environments, cold or hot temperatures,
high pressures, difficult accessibility, etc. are all critical factors when developing
a suitable and cost-effective offshore maintenance and support strategy. This
strategy will take into consideration the environmental influence on
performance of maintenance activities in order to guarantee the shortest
possible downtimes and less costly intervention services.
This study focuses on the effects a challenging environment has on the
maintenance strategy developed in the offshore oil and gas industry. Interviews
with Maintenance and Inspection staff from Shell Assen as well as intensive
research have been carried out. Due to the information obtained and significant
corrosion issues dealt with offshore, the maintenance strategy is developed for a
fixed offshore platform located in a corrosive environment. Using the
information obtained from the investigation, a suitable maintenance strategy is
developed using the Analytic hierarchy process (AHP).

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1.3. Aim and objectives.
The aim of this research is to integrate the Analytical Hierarchy Process (AHP), to
select the most appropriate maintenance strategy for a challenging environment faced
by offshore platforms. Whilst providing new insight into the capability of the AHP
methodology.
In order to achieve this aim:
1. Explore the challenges met in the offshore environment.
2. Examine the capabilities of the AHP methodology.
3. Research the maintenance strategies utilized on an offshore platform.
4. Investigate the critical equipment on an offshore platform.
5. Interview offshore maintenance and inspection supervisors at on oil and gas
company. (Shell Assen)
1.4. Research questions.
The following research questions were framed in order to fulfill the aim of the
research.
RQ1: What are the critical maintenance issues that occur in an extreme
environment on an offshore oil platform?
In an extreme offshore environment, maintenance issues are a major challenge. With
the temperature extremes and conditions faced in places such as the North Sea, Arctic,
and other equatorial settings, the challenges of operating in an offshore setting
increases. Hence, it is vital maintenance personnel are aware of the possible critical
maintenance issues a platform may run into in specific environments, in order to be
better prepared and avoid unplanned maintenance.

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In seeking answers to the major question the study will also address the following
sub-questions:
RQ 2: What current maintenance strategies exist for extreme environments?
Extreme environments are faced by many structures or different equipment’s, such as
marine vehicles utilized in sub sea functions, wind turbines, etc. An awareness of the
possible strategies used to counter similar maintenance issues confronted in different
industries is of great significance in order to identify capable strategies.
RQ 3: What challenges are faced in an offshore environment?
The demand for energy, together with the lack of supplies of traditional fossil fuels
specifically in locations where they are easily accessed, has pushed oil and gas
industry to explore new geographical areas. This search has progressed towards some
of the earths most remote, extreme and vulnerable environments where temperature,
water and drilling depths have all been altered dramatically.
1.5. Delimitations
The research conducted focuses on the maintenance of the offshore platform in
extreme environments. This scope has been to provide a suitable maintenance strategy
using the Analytical Hierarchy Process (AHP). The researcher has limited the
dissertation to case studies and interviews due to time constraints involving company
clearance to obtain relevant data showing downtime and maintenance issues on an oil
platform.
1.6. Structure of paper
Chapter 2 presents Literature review based on the aim of research and methodology.
Chapter 3 offers a brief overview of the offshore oil and gas industry. Chapter 4

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summarizes the methodology utilized in the dissertation as well as findings from the
methodologies carried out. Then, Chapter 5 presents the data analysis section, where
the steps, calculations and results are illustrated. Finally, in chapter 6, the discussion,
conclusion as well as further work obtained from the conducted research is presented.

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CHAPTER 2
LITERATURE REVIEW
This section contains a review of state of literature for the topics that will be
presented in the thesis. The topics addresses the influence of the uncertainty caused
by offshore environmental challenges as well as the proposed method for optimizing
offshore platforms. It also contains a review of studies analysing the Swiss cheese
model, a safety critical model developed my James Reason.
2.1. Challenges met in an offshore environment.
Studies have shown that offshore industry face regular engineering and functional
challenges due to its harsh offshore environments.
The operations of the offshore industry are quite complex (Omoh and Haugen, 2013)
and the growing offshore sector presents a series of on-going challenges (maritime).
Patrick Philips (2015) analogy states that " Onshore is the mission control centre and
offshore is the space shuttle". The offshore and onshore models operate in contrasting
work environments (Patrick and Philip, 2015).
There are major challenges that has to be overcome " to ensure the space shuttle and
their control centre are working in tandem"
2.1 A. Structural damage
“The main hazards on offshore installations are the process fluids and processing
operations, the sea environment, and the process links between the reservoir and other
installations.” (Khan and Amyotte, 2002). Concluding that, “Little can be done to

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eliminate or reduce the environmental hazards, except building the installation
onshore...” The authors objective is to present a complete picture of inherent safety
application in offshore oil and gas activities. They determine that the elimination of
hazards on an offshore facility will be met with resilient difficulty because the hazards
are related directly to the function of the facility. “Some important design
considerations are peak loads created by hurricane wind and waves, fatigue loads
generated by waves over the platform lifetime and the motion of the platform.”
(Sadeghi, 2007). Furthermore Sadeghi (2007) stressed that the hazards in the offshore
industry are predominantly functional.
Mansfield (1992) analyses environmental effects on structural integrity. In
relation to onshore environments, Mansfield indicates that “Onshore the
relevant building regulations and experience should ensure adequate design for
normal and exceptional environmental loads such as snow and wind loadings.”
In comparison to the offshore environment he reiterates, “Offshore the greater
severity and uncertainties of environmental conditions place a high demand on
the structures and their foundations.” Bar-Cohen and Zacny (2009) touch on
structural threats generated by the offshore environment “The seafloor represents
some of the most extreme environments for drilling on earth.” They justify this
statement by describing the seafloor as a combination of high pressures and
temperature extremes in a corrosive and electrically conductive medium. Dey et al.,
(2004) makes reference to frequent corrosion from recurrent contact with seawater,
“The chemical reaction between the pipe metal and the seawater causes an
external corrosion.” This ties in with the functional hazards mentioned by Khan
and Amyotte as described above in paragraph 2.1a. (2002). Dey et al., (2004)
reiterated that external erosion is a non-malicious damage. “ Which is caused by
solid substances in the sea water when they come in contact with the pipelines.”
(Dey et al., 2004).
2.2 B. Logistic challenges
“Logistics typically refers to activities that occur within the boundaries of a single

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organization.” (Hugos, 2011). Hugos goes on to define the activities that occur within
an organization. “ Also, traditional logistics focuses its attention on activities such as
procurement, distribution, maintenance, and inventory management.” That being said,
“Logistical planning of the offshore supply chain can be a real challenge. Multiple
disruptions and incidents may happen in every state without the planners being able to
foresee situations that may arise.” (Oleivsgard, 2013). “Logistics management of
maintenance is a very critical task in the offshore wind energy industry. It also
becomes more crucial for wind farms located in cold, icy or remote areas where the
accessibility for maintenance is restricted.” (Shaifee, 2014). “Any failure to deliver
proper maintenance logistics due to lack of spare parts, unavailability of means of
transportation, or insufficient staffing may adversely affect the wind farm availability
and thereby reducing power output as well as profitability.” (Shaifee, 2015). Lindqvst
and Lundin, in their study on spare part logistics and optimization for wind turbines
(WT) state that “Inadequate spare part stocks can lead to WT unavailability and loss
of revenue if subsystems or items fail and cannot be replaced.” (Lindqvst and Lundin,
2010). They suggested that “ when a spare part is needed but missing in stock, it has
to be ordered from a supplier. Depending on the lead-time of the spare part this causes
operational downtime.” (Lindqvst and Lundin, 2010). Nadili (2002) examined the
logistical as well as inventory challenges of floating offshore wind farms based on
data of components in a wind turbine. (Nadili, 2002) concluded that, available spare
part is one challenge in terms of providing flexible solution to ensure a short lead-
time for spare parts delivery. “The availability of onshore wind turbines is typically in
the range of 95-99% while for early offshore projects an availability as low as 60%
has been observed at some wind farms due to serial failures and harsh weather
conditions.” (Besnard, 2013).
From the literature supplied the authors agree that the offshore environment is one
plagued with uncertainties. These uncertainties have a negative effect on both the
offshore structure and logistics of the industry.

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2.2. Selecting a maintenance approach using AHP
multiple criteria decision-making.
“The AHP is a method that derives ratio scales from reciprocal comparisons. It is a
method of breaking down a complex situation into its component parts, arranging
these parts, or variables, into a hierarchic order, assigning numerical values to
subjective judgments on the relative importance of each variable, and synthesizing the
judgments to determine the overall priorities of the variables.” (Labib et.al, 1998).
However, Studies on maintenance systems in practice show that some managers are
unaware of the different types of maintenance policies (Shorrocks and Labib, 2000)
and selection methods.
Labib et.al. Propose “a three stage system that can handle multiple criteria decision
analysis, conflicting objectives, and subjective judgments. Moreover, the
methodology facilitates and supports a group decision-making process. This
systematic, and adaptable, approach will determine what specific actions to perform
given current working conditions.”Arunraj and Maiti (2010) used AHP and goal
programming to select a maintenance policy in a chemical factory. They concluded
that, by choosing risk as a criterion, predictive maintenance is favored as a periodic
maintenance strategy. Likewise, when cost is chosen as a criterion. Additionally,
Triantaphyllou et al. (1997) proposed using the AHP system primarily with respect to
the four criteria of cost, reliability, repair capability and availability.
“In the conventional AHP, the pairwise comparison is made by using a ratio scale.
Even though the discrete scale has the advantages of simplicity and ease of use, it
does not take into account the uncertainty associated with the mapping of one’s
perception (or judgment) to a number.” (Erkayman et.al. 2012). Deng (1999)
suggests a fuzzy approach to tackle the uncertainty and inaccuracy of human
behavior. Wang et.al. (2006) Also proposes a fuzzy AHP approach to mitigate the
“imprecise judgments of the decision makers…” Although, a new fuzzy prioritization

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method is deduced “In order to avoid the fuzzy priority calculation and fuzzy ranking
procedures....”
Pariazar et.al. (2008) Illustrates the use of an AHP improved by the Rough set theory
to eliminate the inconsistency commonly existing in the AHP method. They consider
the use of the concept of attribute significance in rough sets theory proposed by Wang
(2001) to eliminate evaluation bias problem in AHP. Pariazar et.al. Makes use of a
case study to demonstrate the application of the various steps of the proposed
methodology.
Zaim et.al. (2012) Investigates, two of the commonly utilized methods for decision-
making, namely the Analytical Network Process (ANP) and the Analytical Hierarchy
Process (AHP), are used for the selection of the best maintenance policy. He
determines that, “The ANP method is useful for getting more accurate and effective
results in complex and crucial decision making problems.” However, Bevilacqua and
Braglia (2000) describe an application of the Analytical Hierarchy Process (AHP) for
selecting an ideal maintenance strategy for a major Italian oil refinery. They intend to
improve the effectiveness of the AHP methodology by coupling the AHP
methodology with a sensitivity analysis; this is a determination technique, used to
conclude if an independent variable will impact a particular dependent variable under
a given set of assumptions.
From the Literature supplied, it is clear that the AHP method can be implemented
using different schemes to better select a suitable maintenance strategy. The authors
agree that the uncertainty created by the decision maker will upset the effectiveness of
the AHP method. Additionally, the selection of the criterion is based on the industry.
Nevertheless, cost is a likely to be considered.
2.3. Maintenance strategy utilized on an offshore oil
platform

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Here papers relating to the maintenance strategies used in the offshore oil and gas
industry will be reviewed. Some of which include case studies that exemplify
maintenance strategy applications on static equipment’s such as pipelines and
pressure vessels and rotating assets such as pumping systems and certain topside
process components.
According to Mandal and Syan (2016), The Oil & Gas industry is a case that requires
an industry specific maintenance approach. “Mainly the upstream gas industry can
make significant headway in asset maintenance by adopting philosophies and
strategies, especially with respect to offshore platforms...” (Alsaidi et al., 2014).
Alsaidi (2014) goes on to suggest, “Present maintenance strategies are not
commensurate with ever increasing magnitude of complex equipment maintenance.”
The author proposes that by utilizing TQM (Total Quality Maintenance), equipment’s
could be well maintained and avoid running into trouble in the future. Alsaidi believes
that with a TQM environment, leadership substitutes supervision. It “eliminates
distances among departments and sections, and promotes self improvement measures
as education and training for all concerned.”
“Reliability is the probability that a product or service will operate properly for a
specified period of time (design life) under the design operating
considerations…”(Elsayed, 1996). According to (Andrews and Fecarotti, 2015) “the
reliability performance of any system is a function of its design and the maintenance
strategy employed.” Retd (2012) coincides with this and infers that, “Operation and
maintenance strategies are strongly linked to the reliability and accessibility of the
operating assets.” Rasusand (1998), discusses the Reliability centered maintenance
approach (RCM) as well as the steps in that approach. His research details the
applicability of the approach, “RCM has now been applied with considerable success
for more than 20 years; first within the aircraft industry, and later within the military
forces, the nuclear power industry, the offshore oil and gas industry, and many other
industries.”(Rasusand, 1998). In his article on Strategic Maintenance Planning, Kelly

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(2006) referred to an RCM study on an oil and gas extraction platform. He explained
that the entire operation was broken into just over 100 subsystems before finding out
that 24 of the subsystems accounted for over 80% of the total maintenance man-hours
expanded. Furthermore Kelly (2016), detailed that the maintenance regime for half of
the 24 subsystems were dictated by either legislative or code-of-practice mandatory
requirements and could not be changed. This limited the RCM study to “the
remaining dozen subsystems, which accounted for approximately 50% of the man
hours.” (Kelly, 2016). He reiterated that the final result of the study revealed a
predicted workload cut in half and a reduction in the total expected maintenance
workload for the platform.
“Many companies are investigating the broader implementation of automation to
reduce the number of employees required and the risks they are subjected to in a bid
to improve efficiency and decrease human error and risks.” (Telford, 2011).
Furthermore, Telford (2011) suggests that Proactive or preventative maintenance
(PM) strategies are an essential component of an effective maintenance program. He
goes on to state “There is also an increase in un-manned facilities, particularly in
remote locations. These two trends will inevitably increase operating costs.” (Telford,
2011). “CBM strategies are currently a major focus of maintenance and maintenance
management research due to the aforementioned trends and challenges, as well as
increased complexity in industrial technologies.” (Swanson, 1997). “The PM strategy
known as condition-based maintenance (CBM) provides a dynamic understanding of
equipment condition while in operation and is used to predict failure in mechanical
systems through fault diagnosis from condition monitoring signals using diagnostics
and prognostics.” (Heng et al., 2009).
Gola and Nystad (2011) consider a practical case study concerning maintenance of
choke valves in offshore oil platforms. They aim to develop a condition monitoring
system capable of providing reliable calculations of the erosion state based on
collected measurements of physical parameters related to the choke erosion. As well
as to develop a prognostic system that can accurately estimate the remaining useful
life of the choke. Padmanabhan (2009) refers to Reciprocating Compressor as “the
workhorse of refineries, petrochemical and oil production units.” The author expands

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on the implementation of the CBM approach and illustrates monitoring parameters
utilized on rotating equipment located on an oil platform.
“Any downtime on offshore oil and gas platforms is expensive, which is why planned
maintenance is essential” (Marathon Oil UK). A case study was used to illustrate
maintenance performance on the three platforms utilizing the new technology. The
case study report explains that “The system carries out routine daily checks that flag
up any delays or problems, allowing planners to reschedule work as and when
required to maximize efficiency, safety and resources” (Marathon Oil UK). Marathon
Oil UK’s drive to improve efficiency in maintenance planning as well as managing
unexpected complications led to the invention of an advanced solution based on
Microsoft Project Server and SharePoint technologies.
2.4. Application of the Swiss CheeseModel
Articles explaining the application of the Swiss cheese model are presented and
analyzed. Modifications to the model to fit different industry specifications are also
reviewed.
The Swiss cheese model is an organizational model used to analyze and represent the
causes of systematic failures or accidents (Reason, 2000).
“In practice however, such accident modeling based on the Reason model proved
difficult to apply, resulting in an increasing amount of varieties and simplifications.”
(Sklet, 2004). “Most of the models restrict themselves to the work and technical
systems levels and exclude the technological nature and development of the inherent
hazards.” (Stoop and Dekker, 2010). “Much of the accident data are conceptually
flawed because of the inadequacies of underlying accident models in existing
programs.” (Benner, 1985). “Despite some criticism, the simple model has been
widely taken up in risk analysis and risk management, especially in safety critical
fields where human operators play an important role in incidents, for example, in
aviation, nuclear, petrochemicals industries and, indeed, healthcare.” (Li and
Thimbleby, 2014).

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Ayyub (2014) sates that the methodology is commonly used in aviation, engineering,
and health care, and is capable of describing a scenario that can lead to a series of
events that must occur in a specific order and manner that will ultimately result in an
accident. “The principle idea of the model basically like cheese slice, has holes of or
latent condition.” (Hassan, 2014), “If holes can be visualized and the relationship
between holes and latent conditions can become clear, then it is possible to control the
occurrence of holes. “ (Fukuoka and Furusho, 2016). The authors carried out their
research to determine the relationship between latent conditions and the
characteristics of holes by analyzing 84 serious marine accidents. In their study they
define latent conditions as the following “(1) inadequate passage planning, (2)
inadequate procedures, (3) inadequate rules or deviations from rules, (4) inadequate
human–machine interface, (5) inadequate condition of equipment, (6) adverse
environment, (7) inadequate conditions of operators, (8) inadequate communication,
(9) inadequate team work at a local workplace, and (10) inadequate management in an
organization.” (Fukuoka and Furusho, 2016).
“Reason’s Swiss cheese model was originally developed for domains such as oil and
gas, aviation, railways, and nuclear power generation.” (Beuzekon et al., 2010)
Kujath et al., (2010) present and discusses accident prevention model for offshore oil
and gas processing environments. In their study they discuss the application of the
Swiss cheese model by collecting data on offshore oil and gas process accidents in
order to compile a listing of hazards and to evaluate risk. “The predominant reported
reasons for hydrocarbon releases are: loose bolts on flanges, loose flanges, damaged
flange seals, incorrect welds, loose fittings, faulty valves, switching generator fuels,
overfilling of tanks, open access/vent/valve, safety instrumented system failures,
damaged hoses, equipment start up, seal failures, and pump over- pressure. The
reported sources of ignition are: turbine gas leak, hot manifold, short circuit due to
water ingress in electrical panel, welding and grinding, and bearing overheating.”
(Khan et al., 2010). They further state that other possible causes of accidental
hydrocarbon releases are: vibration, corrosion and release of inert nitrogen from
within a tank. Khalique (2016) explore basic offshore safety and express the
importance of incorporating asset integrity barriers, to an asset integrity management

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system (AIMS). They suggest doing so with a Swiss Cheese Model; “ Each
component within a system whose failure can lead to an accident is referred to as a
‘safety critical element’ and therefore considered as a barrier to prevent accident.”
(Khalique, 2016). “High technology systems have many defensive layers: some are
engineered (alarms, physical barriers, automatic shutdowns, etc.), others rely on
skilled individuals (anaesthetists, surgeons, pilots, control room operators, etc.), and
yet others depend on procedures and administrative controls.” (Beuzekon et al., 2010)

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CHAPTER 3
OVERVIEW
This chapter covers a brief summary of the Oil and Gas industry. Whilst focusing on
the offshore industry, its platforms and the critical equipment’s located aboard the
offshore structures.
3. Oil and Gas Industry
The oil and Gas industry is vital to the economy and to our everyday life. According
to UKOG oil has become the world’s most important source of energy since the mid-
1950s. As it continues to fuel our cars, heat our homes and cook our food, just to
name a few. It is a large and diverse industry made up of three integral sectors:
Upstream, Midstream and Downstream.

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Figure 1: Illustration of the three integral sectors of the Oil and Gas Industry.
(https://media.licdn.com/mpr/mpr/shrinknp_800_800/AAEAAQAAAAAAAAXq
AAAAJDVhYTgwOGUyLTgxNjEtNDZkOS04MGFkLWE3OTA3Y2I3YzdlMg.
jpg)
Midstream
The mid stream sector includes some parts of the upstream and downstream sectors,
but its main function is the gathering and storing of the unrefined oil and natural gas
also referred to as the raw produced products. They are gathered and stored before
being transported by pipeline or boat to refineries.
Downstream
The Down stream sector is also referred to as the refining sector. Here the refining of
crude oil and the selling and distribution of natural gas and products attained from
crude oil, takes place. The downstream sector is made up of oil refineries,
petrochemical plants, petroleum distribution outlets, retail outlets and natural gas
distribution companies. This sector is in direct link with the consumers.
Upstream
The upstream sector also known as the Exploration and Production (E&P) sector is
the part of the industry that deals with obtaining the crude oil and natural gas from
under ground or underwater (Onshore and Offshore) and bringing it up to the surface.
It involves exploration of potential oil and gas fields including the drilling and
operation of those wells. This sector is pivotal to the structure of the industry due to
its rewarding yet complex and risky quality. This sector is greatly affected by external
elements such as, political instabilities, international conflicts, and even seasonal
weather patterns.
3.1. Offshore Industry
More than two thirds of the earth’s surface is covered in water. This begs to reason
that oil and gas are found and produced not only on land but also at sea. According to

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EDP Solutions, in the oil and gas industry, “Offshore” refers to the development of oil
fields and natural gas deposits under the ocean. Offshore oil and gas production,
Involves extracting oil and gas from beneath the sea, it is a critical component of the
world’s energy supply. “Offshore has provided nearly 70% of the major oil and gas
discoveries worldwide in the last decade.” (Sandrea and Sandrea, 2010). This
industry is responsible for twenty percent of oil reserves and 45% of gas reserves.
According to the Organisation of Economic Co-operation and Development, in 2014
Offshore oil production amounted to 21.5 million barrels per day and offshore gas
production amounted to 90 billion cubic feet per day (BCFD) which in turn accounted
for approximately one quarter of the worlds oil and gas production. In Planete
Energies report “The challenges of Oil and Gas Production” (2015), it is implied that
the offshore industry accounts for 30% of global oil production and 27% of global gas
production. The report suggests that these percentages have remained stable since the
early 2000s and are unlikely to change any time soon.
3.1.1. Offshore Exploration and Planning.
The purpose of exploration is to identify commercially viable resources of oil and gas.
Locating such reservoirs and estimating the likelihood of them being a possible
resource is a time consuming and complicated process. This process requires the use
of a range of techniques, such as deep and shallow geophysical (seismic) surveys,
shallow drilling and coring, aero-magnetic/gravity surveys and exploration and
appraisal drilling. The most popular combination utilized by most oil companies is,
seismic surveys and exploratory drilling.

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Figure 2: Diagram showing Seismic survey.
(https://krisenergy.com/images/offshore%20seismic%20survey.jpg)
Once exploration discovers oil and gas reserves with a prospect for a good economic
return, the next step is to figure out the best way to extract it. The target location for
drilling is determined, specific objectives are devised early in the planning phase
where the nature and cost of the well to be drilled is defined. This is a long and
strenuous process that can take even longer than the exploration process. These
objectives determine how long the well will take, the range of tests required as well as
the surface hole location (rig positioning). Before a well is drilled information is
gathered on the stability of the surface sediments and potential subsurface hazards.

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Furthermore, before a drilling operation can be scheduled the following are taken into
account:
• The weather and current conditions
• Seasonal environmental conditions and license conditions
• Availability of rigs
• Commitments made to government
• Other company internal constraints and objectives
(Department of Trade and Industry, 2001).
3.1.2. Offshore Production.
Before the production process can begin a well must be drilled to reach the reservoir.
This process is specifically carried out by a mobile drilling platform. After the drilling
platform is removed a production platform is then installed over the borehole using a
barge equipped with heavy lift cranes. The oil and gas are extracted and then
processed.
Extraction
The retrieval of oil and gas from deposits deep in the sea floor requires the use of
sophisticated equipment and highly skilled personnel. Offshore oil extraction is
carried out using offshore drills and involves the operation of wells on the continental
shelf; this sometimes occurs in waters that are hundreds of feet deep. Once the well
has been drilled, a production casing is installed. This casing is fixed to close the well
and control the flow of petroleum. Explosives are then sent below the ground to crack
the production casing at different depths allowing oil and gas to enter the well in a
controlled manner and moved to the surface at a reasonable pressure. When initially
drilled, the pressure produced by the reservoir is enough to transport oil to the surface
but as time passes the pressure drops and pumps are needed for this process to
continue. Different methods are used to the pressure and flow of oil to the surface;
sometimes water or gas is pumped into the reservoir, or in some cases steam is sent
down to the well to heat the petroleum. Because the liquid brought up to the platform

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is a mixture of crude oil, natural gas, water, and sediments. Offshore processing of the
raw material takes place.
Production
The aim of the processing is it to convert raw produce or well fluid into a marketable
product (Crude oil, gas, and condensate). Initially, Subsea hydrocarbon equipment
was only utilized for oil extraction. Gas was separated from liquid hydrocarbons
under water, and then the extracted liquid hydrocarbons were pumped to the surface
and gas also under its own pressure. Currently, offshore production technologies are
highly capable. The offshore production process is made up of a number of operations
that allow for a safe and reliable production of petroleum and natural gas from
flowing wells. The fundamental operations that are carried out on an offshore
platform include:
 Produced hydrocarbon separation;
 Gas processing;
 Oil and gas export;
 Well testing;
 Produced water treatment and injection;
 Seawater lift for cooling duty and injection; and
 Utilities to support these processes.
(Azeri et al., 2004)
The figure below shows operations in different stages.

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Figure 3: Production process
(http://www.offshorepost.com/resource/production-process-overview/)
3.2. Offshore platforms.
“Around the world, until 2013, there are more than 6500 offshore oil and gas
installations distributed in about 53 countries.” (Misra, 2016) Offshore platforms are
massive structures equipped with facilities to drill and extract oil and gas from wells.
With onshore drilling the ground provides a platform from which to drill, however at
sea an artificial drilling platform must be constructed. That being said, it should be
noted that an oil rig and oil platform are completely different. An oil rig is in most
cases is part of an oil platform that deals primarily with drilling and completion of
wells whilst an oil platform covers many more facilities. Including having an oil rig,
it includes a wellhead, helipad, utility systems, quarter etc. (Dalvi, 2015).
3.3.1. Platform Type and Design
According to Sammie (2016) the systems and equipment installed in an offshore
platform depends on its planned functions and crude oil type or composition.
Furthermore, is the offshore platform is intended for oil or gas plants? Does it perform
any processing or is it simply a wellhead platform? Does it also include an enhanced
oil recovery (EOR) package? Is it a living quarter platform? These facilities are
located on the topside of the offshore platform as seen in Figure 2. Because the
Topside is designed to accommodate wellheads, trees, piping manifolds, wellhead
control panel, and any other required facility, the size of the platform depends on
those facilities required.
Many permanent offshore platforms are equipped with a full oil production facility
onboard. It is in this facility that the processing of production fluids from oil wells is
carried out. A process system can be located on a production or wellhead platform,
the main intention of the system is to separate the key components such as; gas, oil
and water or to guide crude flow by pressure, temperature and volume regulation.
Before they are prepared for export to offshore or floating loading facilities.

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Figure 4: An example of offshore platform structure and its facilities. (Northwest
Hutton field Platform).
(http://www.offshore-technology.com/projects/hutton-field/hutton-field2.html)

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The type of platform used depends primarily on the depth of the water and the
environmental conditions. Drilling for oil and gas offshore in most cases hundreds of
miles away from land presents a number of challenges compared to drilling onshore;
where vast water depths does is not influence onshore platforms. The platform and
rigs used in shallow waters are very different from those used in deep-water. Figure 3
illustrates the different platforms and rigs available and the depths at which they are
used.
Figure 5: Offshore oil platforms designed for different water depths.
(http://cdn2.hubspot.net/hubfs/514555/images/blog/offshore-cables-topside-
modules1.jpg)

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According to the US Mineral Management Service (MMS), the water depth can be
classified as shown below.
Shallow water < 350 m
Deepwater < 1500 m
Ultra deep water > 1500 m
There are two types of offshore drilling rigs and platforms. They are known as a
moveable (Floating) or fixed platform. Offshore platforms can be classified as fixed
platforms, compliant towers, jack-up platforms, semi-submersible platforms, tension-
leg platforms (TLPs) and SPAR platforms. Due to the scope of this research the focus
will be on the Fixed platform.
Fixed Platform
A fixed platform is a type of offshore platform capable of working in depths of up to
1,500 feet, which offers stability in place of mobility. They are costly to build and
often require a large oil discovery to justify their construction. A fixed platform can
be described as being made up of two main components; the “substructure” and
“Superstructure”. The “Superstructure” which is also referred to as the topside, acts as
home to drilling rigs and production facilities such as gas turbines, generating sets,
pumps, compressors, a gas flare stack, revolving cranes, survival craft, helicopter pad
and also offer accommodation facilities for crew. The tops side can weigh up to
40,000 tonnes. That being said it is only expected that the base structure also known
as the “substructure” is designed to handle such a considerable weight.

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Figure 6: Fixed Concrete Offshore Platform.
(https://wikiocean.wordpress.com/2012/02/13/troll-a-platform-the-tallest-
construction-ever-moved-by-mankind/)
The fixed platform is typically built on steel or concrete legs that are fitted and
supported by the seabed. With some concrete platforms, the weight of the legs and
seafloor platform is so great that it allows the platform to rest on its on mass instead
of being attached to the seafloor. In most cases a fixed offshore oil and gas production
platform is made up of steel legs also known as a “ steel tubular jacket”.

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Figure 7: Fixed steel “Jacket” Platform.
(http://www.esru.strath.ac.uk/EandE/Web_sites/98-9/offshore/rig.jpg)
(http://www.2b1stconsulting.com/wp-
content/uploads/2012/08/Jacket_Platform.jpg)

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3.4. Critical equipment in the Oil and Gas Industry.
“An effective maintenance program is founded on a critical equipment list developed
through a rigorous analysis of the probability of failure and the consequences of
failure.”(Townsend, 2011). According to Alexis and Rounds (2016) critical
equipment is any equipment or a machine that is capable of significantly impairing
the ability for a business to safely meet its objectives, adversely affect quality levels
and violate environmental standards of the business organization.
Critical equipment in the oil and gas industry can be categorized into two main
sections; Safety critical and Operation critical.
3.4.1. Safety Critical.
Health and Safety is an important factor for every industrial sector, but this is
particularly so for the offshore oil and gas industry where there is high potential for a
major accident. The HSE (Health and Safety Executive) describe the safety critical
Elements as “parts of an installation and such of its plant (including computer
programmes), or any part of thereof-
(a) The failure of which could cause or contribute substantially to; or
(b) A purpose of which is to prevent, or limit the effect of a major accident. “
(HSE, 2016).
What this implies is that any structure, plant equipment, system; including computer
software or component part whose failure can contribute to a major accident or impair
or limit the effect of a major accident, is classified as safety critical. In the figure
below reference is made to the Integrity Barrier “Swiss Cheese” Model of Shell EP.

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Figure 13: Integrity Barrier “Swiss Cheese” Model of Shell EP
In the early nineties, James Reason developed the Swiss cheese model. The model
acts as an illustration for accident causation utilized in risk analysis and risk
management, in sectors such as aviation, engineering, healthcare, and as the standard
behind layered security. The ideology is a comparison of human systems to multiple
slices of Swiss cheese, stacked side by side, in which the different layers represent the
types of defense put in place to relieve the risk of a threat becoming reality. In theory,
a lapse or weakness; which are characterized, as the holes in one defense should not
allow a risk to materialize, because another defense also exists, to prevent a particular
point of weakness. The original Swiss cheese model can be seen in Appendix A.

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The model in Figure 12 is an incorporation of that model to the safety critical
elements at shell. The safety critical elements are listed under each threat and
escalation category
3.4.2. Safety critical equipment
The SCE (safety critical elements) in figure 12 have been divided into “Hardware
barriers”: Structural integrity, Process containment, Ignition control, Detection
systems, Protection systems, shutdown systems, emergency response and life saving.
According to the “Safety Critical Element Interpretation Document NAM Asset Land”
and “ONEgas Asset East (NL)”, each element has been categorized under certain
discipline of accountability. For the purpose of this study the main focus will be on
the mechanical safety critical equipment’s on an offshore production platform.
Hardware Barrier: Structural integrity
Structural integrity is described as the ability of an item to hold under a constant
load. Dr. Steve Roberts describes it as the “the science and technology of the margin
between safety and disaster.”
Heavy lift crane
A heavy lift crane is simply a type of machine equipped with a hoist rope, wire rope
or chains, and sheaves capable of transporting and handling items that typically weigh
over 100 tons and of widths and heights of over 100 meters. In the offshore industry
these include parts of rigs and production platforms. Overhead cranes or any
mechanical handling equipment at an offshore location are safety critical equipment
since failure could cause or contribute to a major accident or harm personnel.
“Dropped objects from cranes are one of the major risks on offshore installations.”
(Dropsafe, 2016)

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Figure 14: A Heavy Lift Crane
(http://www.cargotec.com/en-global/newsroom/media-
bank/solutions/HighResolutionImage/hires_offshore-2012-05.jpg)
Hardware Barrier: ProcessContainment
Process containment in the oil and gas industry indicates equipment that contains
dangerous substances, such as highly toxic and flammable properties. These
containment systems are considered safety critical if they provide primary
containment under normal operating conditions and if failure directly causes a loss of
containment into the atmosphere or into non-hazardous system, resulting in the

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release or over pressurization which may in turn result to a fire or explosion with the
potential to cause death or serious harm and a serious environmental impact.
Pressure Vessels
Pressure vessels are normally designed, constructed and installed according to the
recognized pressure vessel code or standard. They contain hydrocarbons, chemicals or
other substances that are required under normal operating conditions. An Offshore
platform typically has a number of safety critical pressure vessels. Such as, slug
catchers, separators and flare knock out drums and flare stacks.
Slug catcher
A slug catcher is a static equipment that plays an important role in oil production. It is
an essential equipment located at the receiving terminal of a multiphase-flow
processing plant. It is used to accumulate liquids that have settled in flow lines to
prevent an overload in the plant.
Figure 15: Slug catcher
(http://www.europipe.com/fileadmin/europipe-modern/images/europipe-slug-catcher-
grafik.png)

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Separators
An oil and gas separator is a cylindrical pressure vessel used to separate oil, gas and
water from a well stream. A separator can be vertical or horizontal and classified as a
two-phase or three-phase separator. A two-phase separator deals only with oil and
gas, while the three-phase deals with oil, water and gas.
Figure 16: Illustration of a three-phase Horizontal Separator
(http://www.piping-engineering.com/crude-oil-processing-offshore-
facilities.html)

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Flare Knockout drums
A knock out drum is a crucial part of a flare system (A system that collects and
discharges gas from pressurized process safely into the atmosphere). It is located
before the flare ahead as shown in Figure 15. This process containment vessel is put
in place to prevent liquids from entering the flare stack, which in turn prevent
spewing out burning liquid into the atmosphere.
Figure 17: Flare system
(http://www.flarenotice.com/images/flaringinfo/clip_image004.png)

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Figure 18: Illustration of a Flare system on a platform
(http://www.thecyberhawk.com/wordpress/wp-content/uploads/2012/07/Offshore-live-
flare-inspection-3.jpg)
Heat Exchangers
Heat exchangers that contain hydrocarbons or another dangerous substance in at least
one side of the exchanger are considered safety critical. The goal is to maintain
integrity of the pressure-bearing envelope. The typical scope of a safety critical heat

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exchanger is the pressure-containing envelope, that is the shell and supports and all
welded connections or tapings connected to it, including nozzles, instrument and
small-bore appendages up to and including the first mechanical joint(s).
Typical safety critical heat exchangers are process hydrocarbon heat exchangers, like
inlet gas cooler, gas or gas heat exchanger and off-gas cooler and chemical treatment
heat exchangers, like glycol dehydration systems.
Figure 19: Gas Exhaust Heat Exchanger.
(http://www.power-technology.com/features/feature109722/feature109722-5.html)
Rotating Equipment
Rotating equipment is safety critical equipment because failure of any component can
cause a loss of containment resulting in a fire, explosion or release of a dangerous

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substance with potential to cause death or serious injury to one or more persons. It
covers pumps, compressors, turbo-expanders and gas turbines for generating electrical
power. The typical scope of a safety critical pump, compressor or turbo-expander is
the pressure-containing envelope. That is the equipment shell including the suction
and discharge flanges or mechanical joints and all welded connections or tapings
connected to it, including all nozzles, instrument and small-bore appendages and
supports.
Some examples of safety critical rotating equipment are process hydrocarbon pumps,
compressors, Gas turbines, water or natural gas condensate loading pumps and
process drain pumps. These are all mechanical equipment’s that essentially move
materials by adding kinetic energy to their process. (Schematics and diagram)
Piping Systems
The idea behind a safety critical pipework is the pressure-containing casing between
the various items of equipment, i.e. all pipework, fittings, flanges, valves, instrument
tapping, instrument tubing, flexible hoses and pipe supports. Critical piping systems
will generally be those, which may contain flammable or hazardous fluids under
normal or abnormal conditions. Piping is considered safety critical if release of a
toxic material represents an immediate risk to one or more persons. A primary
element of instrumentation that is integral part of the piping system (e.g. venturi
flowmeters) and in direct contact with the hazardous medium is also classified as a
safety critical piping system.
Relief System
Relief systems located on safety critical process containment systems are safety
critical in Asset Land. The relief system is designed to protect equipment from over
pressurization if the process control system fails or in case of heat input from outside

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to a blocked-in containment. Safety critical relief components comprise all pressure,
thermal, fire relief valves or discs (also on atmospheric storage tanks), including
associated relief pipework. Elements, which directly influence the capability of the
relief valves and/or rupture of discs, are also safety critical. These include heat tracing
of relief valve pilot lines, control valves (where the valve Cv determines the relief
valve capacity), high-pressure trips and non-return valves.
The figure below shows the schematics for the arrangement of a compress system,
including the relief systems put in place. The symbols in the PI&D (Piping and
instrumentation drawing) have been supplied in Appendix B.
Figure 20: A typical arrangement for a centrifugal compressor system.
(http://www.enggcyclopedia.com/2012/02/typical-pid-arrangement-centrifugal-compressor-
systems/)
Hardware Barrier: ProtectionSystems

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These are systems that have been put in place to reduce the consequences of failures
by providing greater safety and protection in order to prevent loss, damage and
destruction.
Fire Water Pumps
Due to the production process carried out on an offshore process facility, extremely
reliable and effective fire fighting systems must be available. Firewater pumps, if
present are put in place to limit the effects and consequences of fires. It is a pump
system located around the platform connected to a detection system, which In the
event of a fire, open up a valve or series of valves to allow water to flow through to
the fire. Traditional, firewater pumps are conventional, vertical line shaft-pumps
driven by a diesel engine or electric motor. The reliability of a plant’s firewater
pumps is a frequent oversight; this oversight is capable of resulting in a significant
consequence. According to a Rotating Equipment consultant Amin Almasi, a
firewater pump system can account for 15 to 35 percent of insurance deficiency rating
points for a plant. With no thorough planning and the correct equipment, facilities
could see production process slowed down or stopped completely due to uncontrolled
fires leaving themselves vulnerable to high insurance costs.
3.4.3. Operation Critical.
Although there is no direct comparison between the importance of operation critical
and safety critical equipment, it is clear that due to legal requirements and regulations
safety critical equipment pertaining to the oil and gas sector must be clearly managed
and maintained. That being said, failure to properly manage and maintain operation
critical equipment has its consequences. Their availability and capacity to alter
operational efficiency is key to the success of an organization.

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Difficulty arises in classifying operation critical equipment in the offshore industry
because they are classed based on location. A particular piece of equipment at a low
temperature environment may not stand as operation critical equipment at a high
temperature environment. According to Narayanan and Joshy, R.H. Clifton suggested
a five level priority rating based on the basis of efficient operation of the equipment
vital to the production process. That being said, Campos et al., (2015) mentions some
key operation critical equipment in the oil and gas industry. They explain that in oil
and gas facilities the pumping and compression systems require a considerably high
level of availability. Therefore faults that could result in their shutdown must be
minimized and even eliminated. Faults in the critical systems mentioned can lead to
loss in production “as large as 200,00 bbl to certain production limits.” (Campos
et.al., 2015). The issue of failure in a heat exchanger is also considered a major
concern, especially pertaining to offshore platforms as their ability to control the
crude oil temperature affects the efficiency of the separators.
Figure 21: Gas treatment process on a WD143 Offshore Platform.

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(http://images.pennwellnet.com/ogj/images/ogj2/9632jla02.gif)
Table 1: Gas treatment controller systems
PC Pressure controller
FC Flow controller
LC Level controller
SC Surge controller
Figure 21. Illustrates an example of a production critical process where a compressor,
heat exchanger and pumps are utilized. The gas treatment process is a key step in gas
processing; the gas collected from the high-pressure separator undergoes treatment to
remove water. This involves cooling by heat exchanger and compression of the gas
before using glycol to remove any remaining moisture. This step is important in
preventing hydrate formation and corrosion within the gas pipeline.
Power generators are also key components in production on an oil platform. They
provide electrical power for all drilling operations, production operations and all of
the platform utility systems. The Rolls Royce gas turbine generator used on a shell
fixed platform costs approx. 3-4million euros to replace, and its availability is key to
the production of the platform.

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CHAPTER 4
RESEARCH METHODOLOGY
The methodology used in carrying out the research is explained in this
chapter as well as well as a brief explanation on the findings.
4. Research Overview
In this thesis, the Multi Criteria Decision Making method based on the Analytical
Hierarchy Process (AHP), is proposed to select the most appropriate maintenance
strategy for major extreme environments faced by offshore platforms taking into
consideration the environmental influence on performance of maintenance activities.
Whilst providing new insight into the capability of the AHP methodology. The
research was conducted in response to the following research questions (1) What are
the critical maintenance issues that occur in an extreme environment on an offshore
oil platform (2) What current maintenance strategies exist for challenging
environments? (3) What are the challenges faced in an offshore environment?
4.1. Research Approach.
The research presented in this dissertation is predominantly based on qualitative data;
this form of research is specifically exploratory research. Used to gain an
“understanding of a subject and its contextual setting, provide explanation of reasons
and associations, evaluate effectiveness and aid the development of theories or
strategies.” (Office for National Statistics). Maxwell (2005) describes five scientific
goals for which a qualitative approach is suited.

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 Understanding the meaning of the events, situations, experiences and actions
the participants of the study are involved in.
 Understanding the context within which the participants act and how this
context influences their actions.
 Identifying unanticipated phenomena and influences, and generating new
grounded theories about the latter.
 Understanding the process by which events and actions take place.
 Developing casual explanations.
The Qualitative research method will consist of in-depth interviews on maintenance
and inspection staff for Shell Assen, followed by a case study based on the primary
equipment that the proposed methodology will be based on. The interview will be
carried out on both rotation and static maintenance staff including an Inspection staff
member for Shell, Assen, Netherlands. The instrument for this data collection method
is a questionnaire personally designed and generally based on a “criticality analysis”
method. Taking into account the following parameters. (1) Safety critical (2)
Production critical (3) maintenance costs (4) failure frequency (5) downtime length
The design and nature of the interview and case studies further explained in the
following section.
4.2. Research Process.
After researching existing literature based on the research questions mentioned in
section 1.4, an interview is proposed to analyze the basis and importance of
formulating a maintenance strategy suitable for a specific challenging environment.

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4.2.1. Delphi Interview Technique
In-depth interviews are optimal for collecting data on individuals’ personal histories,
perspectives, and experiences, particularly when sensitive topics are being explored.
(Tripathy and Tripathy, 2015). An interview questionnaire was framed, after
researching existing literature on challenging offshore environments as well as the
maintenance strategies applied. The interview process was carried out using the
Figure 22: Delphi method framework
Delphi Method. The Delphi technique is recognized as a systematic, interactive
forecasting method, which typically utilizes a group of experts in order to answer a
series of questions in two or more rounds. The participants of the Delphi method are

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typically experts with a professional insight on the topic. The Delphi method is
exceptionally useful in areas of limited research, since survey instruments and ideas
are generated from a knowledgeable participant pool (Hasson et al., 2000), and it is
suited to explore areas where controversy, debate or a lack of clarity exists.
The performed interview was structured according to the framework shown in Figure
22. The structure is aimed at obtaining a broad range of opinions from the experts
interviewed. The responses obtained from the first round of questions are summarized
and used as the foundation for the second round of questions. Subsequently the results
from the second round feed into the final round.
The steps carried out are presented below:
Step 1: Choose a facilitator.
The researcher in this case acted as the facilitator of the interview.
Step 2: Identify your experts.
The expert is, “ any individual with relevant knowledge and experience of a particular
topic.” (Cantrill et al., 1996). In this case the experts chosen for the panel were a
rotation and static maintenance supervisor as well as an inspection supervisor.
Step 3: Define the Problem.
This step focuses on the problem or issues the research questions aims to understand.
The experts are made aware of the problem at hand and the aim of the research. Here
the researcher explains the need for a robust maintenance strategy in a challenging
offshore environment.
Step 4: Round one questions.
General questions are asked to gain a general understanding of the experts view
relating to the problem at hand. The questions asked of the Maintenance and
inspection supervisors varied. The maintenance staff was asked (1) what environment

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they find the most challenging in regards to maintenance issues? (2) What the critical
equipment on the platforms are? (3) What type of maintenance strategies are used on
the critical equipment’s mentioned?
Whilst the Inspection supervisor was asked to answer (1) what environment they find
the most challenging in regards to maintenance issues and inspection? (2) What
equipment requires frequent inspection? 3) What inspection strategy is employed? (4)
What other factors influence inspection?
The complete phase 1 questionnaire and response from both Maintenance and
Inspection supervisors can be seen in Appendix C.
Step 5: Round two questions.
From the response achieved from the first questionnaire, the second round will delve
deeper to clarify specific issues in order to develop a clear consensus from a common
ground. Due to the primary scope of study pertaining particularly to maintenance
strategies, the following follow up questions were asked only of the maintenance
supervisors. (1) What critical equipment experiences frequent failures/maintenance
calls in the company’s most challenging environment? (2) How long is the downtime
for the critical equipment mentioned? (3) Most expensive equipment to replace or
carry out maintenance?
The complete phase 2 questionnaire and response from both Maintenance and
Inspection supervisors can be seen in Appendix D.
Step 6: Act on findings
In this step the findings are analyzed and a conclusion is made.

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4.2.2. Case study.
These well-documented case studies indicate the effects and capabilities of corrosion
in the offshore industry.
PETRONAS
The Malaysian state owned global energy giant at the heart of B.C.’S LNG ambitions,
was informed in late 2013 that it was going through “very serious” safety and
integrity issues throughout its offshore Malaysian operations. A 732 page internal
audit presented to the senior management on Oct.24, 2013, brought attention to a
number of problems on Petronas oil and gas platforms in three major oil and gas
fields. Four of the issues were described by the auditors as being “almost certain,” if
not fixed, to cause “catastrophic” events. Including what was described as
“systematic” problems relating to the lack of staff, competence and training there
were also more than a dozen references to “severe” cases of corrosion threatening the
structural integrity of the facilities. Auditors found six “pressure vessels” – containers
that hold pressurized gas or liquid--- that had internal corrosion and had not been
inspected for at least 20 years. According to the Vancouver sun, Petronas has cited
concerns about a number of accidents and deaths since 2011, which according to a
sun source led to ordering the 2013 internal audit.
Analysis of the failure of an offshore compressor crankshaft.
Due to the detection of an oil leak on a compressor crankshaft, located on an offshore
oil and gas platform, an inspection was carried out. During the inspection of a North
Sea oil and gas platform a crack was identified on the crankshaft of a compressor. The
crankshaft had been in services for 8 months and after detection of the crack, was

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decommissioned for a failure examination and material analysis to determine the
mechanism of failure. Localized corrosion attack, similar to pitting, was discovered
on the bulk of the crankshaft surface. Along with chlorine residue, located in the base
of the pit like features. This led to the conclusion that the primary mechanism of
failure was undoubtedly corrosion fatigue paired with torsional loading.
4.3. Validity.
The term validity describes to what extent a researcher‘s chosen method is feasible for
the studies of the intended phenomenon (Gummesson, 2000). Based on the capability
of the analytical method (AHP), in utilizing qualitative data to reach a decision, the
research methods of choice are proved valid.
4.4. Findings.
From the Delphi technique and case study utilized in this research, it was concluded
that a corrosive environment is a major challenging environment attributed to the
offshore industry. The research methodologies employed also obtained response
regarding the maintenance strategies used on certain critical equipment on an offshore
platform. It was established that RCM, Preventative Maintenance (PM), Predictive
Maintenance/Condition Based Maintenance (PdM/CBM) and Corrective Maintenance
(CM), were some of the frequently applied maintenance strategy in situations where
corrosion was a factor. Six crucial factors to implementing an optimal maintenance
strategy were established: Safety, Personnel training/capabilities, Loss of production,
inventory and fault identification.
4.5. Corrosion.

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Shaw and Kelly (2006) describe corrosion as the degradation of materials’ properties
due to interactions with their environments...” According to the Shell inspection
supervisor, in the last 3 years Shell offshore platforms have seen 450 occasions of
reported corrosion, 400 of which were external compared to the onshore platforms
where 280 corrosion occasions were reported with only 30 pertaining to external
corrosion issues. In accordance with the Inspection supervisor, both rotation and static
Maintenance supervisors refer to a corrosive environment as the most challenging
offshore environment. As reported by Wood et al., (2013) 137 major refinery
accidents reported by EU countries to the EMARS (EU major accident report system)
database since 1984, around 20% indicated corrosion failure as an important
contributing factor. In consonance with eMars this proportion of refinery accidents
has remained constant well into the 21st century. Corrosion is capable of causing a
release of hazardous substances and components or reducing both the performance
and reliability of equipment until their immanent failure. In essence, the presence of
corrosion is capable of introducing risk to the safety and well being of both plant
employees and the general public as well as lead to severe damage of process units,
and in some cases shutdown of refinery operations.
4.5.1. Environmental influences.
Corrosion develops due to hostile environmental conditions during the life cycle of a
range of industrial structures, e.g., offshore oil platforms, ships, and desalination
plants. There are a number of environmental corrosion factors that are in some ways
unique to oil and gas production. Crude oil and natural gas are made up of a number
of naturally corrosive products, such as carbon dioxide (C O2), hydrogen Sulfide
(H2 𝑆 ), and water ( H2O). Furthermore, other unique aspects are the extreme
temperatures and pressures encountered. Oil and gas production has come a long way.
Due to advancement of technology, deep-water exploration is now a regular factor in
the production of oil and gas. According to Garverick (1994) in deep gas wells;
measured at 6000m (20,000ft.) temperature approaching 230  C (450  F) have been
measured, and partial pressures of CO2 and H2 𝑆 of the order of 20.7 MPa (3000 psi)

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and 48 MPa (7000 psi), respectively, have been encountered. Although oxygen is
typically absent from depths greater than approximately 100 m (330 ft) below the
surface. It is however responsible for the external corrosion of offshore platforms and
drilling rigs. Corrosion can become apparent in two forms, uniform or localized
corrosion. Uniform corrosion, also known as general corrosion is the typical form of
corrosion where an entire surface area undergoes thinning of the metal. “In chemical
processing industries uniform corrosion is considered the least dangerous form of
corrosion because it is easily visible long before it is degraded enough to
fail.”(Frankel, 19983) However, uniform corrosion in some cases are the cause of
accidents if taken for granted, for example, in pipelines that are located in remote
locations, underground, or otherwise and not frequently inspected or maintained,
uniform corrosion may remain undetected.
“Localized corrosion is the accelerated attack of a passive metal in a corrosive
environment at discrete sites where the otherwise protective passive film has broken
down.” (Frankel, 1998) Thus, the effects of localized corrosion can be more
detrimental than that of uniform corrosion due to the increased possibility of failure.
Characteristically, localized corrosion occurs between joints also known as crevice
corrosion or under a paint coating or insulation. Stress corrosion cracking and
hydrogen assisted stress corrosion are both forms of localized corrosion.
4.5.2. Contribution of process and equipment conditions.
The Petroleum Industry is made up of a large variety of corrosive environments.
Prabha et al., (2014) states that corrosion problems occur in the petroleum industry in
at least three general areas: (1) Production, (2) transportation and storage, and (3)
refinery operations. As corrosion in the petroleum industry is vast in all sectors and in
most cases similar, it begs to reason that the damage mechanism of a refinery holds
some similarities with that of Production. That being said the American Petroleum
Institute Recommended Practice 571 (API 571) mentions several characteristic
corrosion damage mechanisms to industrial activity including those specific to
refineries. The table below shows the damage mechanisms found in a refinery.

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Operating conditions in the oil and gas industry, due to its nature are likely to
instigate corrosion failure to initiate a chain of events leading to a major accident.
Corrosion is a serious development capable of creating holes in tubing walls, causing
the release of highly flammable chemicals. Contamination is another leading cause
for surface degradation also known as localized corrosion. Such contamination are in
most cases caused by the introduction of iron particles from welding and grinding
operations; surface deposits from handling, drilling, and blasting; and from sulfur-rich
diesel exhaust. The periodic seawater deluge testing carried out on an offshore
platform, especially in combination with insufficient freshwater cleansing, can leave
behind unwanted chloride-laden deposits, which will promote corrosion.
Table 3: Stress corrosion cracking damage mechanisms proposed by API 571.
Damage
Mechanism
Velocity,
Temperature and
pH Influences
Substances
Involved
Other Influences Processes Affected
Mechanical and Metallurgical Failure Mechanisms
Erosion-
corrosion
High velocity, High
Temperature, High
Temperature, High,
Low pH.
Varied Particularly occurs
in pockets,elbows
and similar
configurations.
Affects all types of
equipment exposed
to moving fluids,
gas‐borne catalytic
particles.
Uniform or Localized loss of Thickness (Generic)
Galvanic
corrosion
Varied
Atmospheric
corrosion 
Low temperature Cyclic: Fluctuation
between ambient
and < or >
temperature.
Cooling
water
corrosion 
Low velocity, High
temperature.
Fresh or salt water,
potential chlorides
High Temperature Corrosion (Generic)

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4.6. Corrosion Maintenance.
According to NACE International, the worldwide corrosion authority. It is widely
recognized within the oil and gas industry that effective management of corrosion will
contribute towards achieving the following benefits:
 Statutory or Corporate compliance with Safety, Health and Environmental
policies
 Reduction in leaks
 Increased plant availability
 Reduction in unplanned maintenance
 Reduction in costs of delay.
Corrosion can account for 60% of offshore maintenance costs; these cost implications
as defined by the HSE (Health & Safety Executive) are direct and indirect costs.
Direct costs pertain to inspection, chemical inhibition, corrosion monitoring and
coating maintenance. Where as indirect costs include Increased maintenance, deferred
production, plant non-availability and logistics. “The goal of corrosion management
is to achieve the desired level of service at the least cost.” (Rogerge, 2007)
Sulphidation High temperature Sulphur
concentration
FCC, coker,
vacuum distillation,
visbreaker and
hydro-processing.
High
temperature
H2/H2S
High temperature H2 and H2S Desulphurizers,
hydrpocessing,
hydrotreaters,
hydrocracking
Nitiriding High temperature Nitrogren
compounds

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Legislation governing activities for topside processing facilities for offshore
installations are important for every offshore platform. These regulations provide a
framework where risks are identified by means of a structured approach and
accompanied by an appropriate set of risk control measures to manage them. The
regulations place an emphasis on the management of corrosion to ensure system
integrity and in turn the safe operation of facilities. This infers that management
systems must include suitable procedures to identify corrosion risks, and where they
pose a threat to the safety or integrity of the facilities, in order to manage those risks.
There are three corrosive zones on an offshore platform, each of which have its own
distinctive corrosion problems: (1) the atmospheric zone (above water), (2) the splash
zone (tidal), and (3) the subsea zone (underwater and sea bottom). For the purpose of
the research the main focus is the critical equipment located on the atmospheric zone
also known as topside.
4.6.1. Corrosion maintenance tasks.
Cathodic protection is one of the most widely used maintenance techniques in
countering corrosion concerns. The offshore industries rely on cathodic protection to
guarantee the integrity and durability of their assets, such as, offshore platforms,
subsea pipelines and marine terminals. Due to the high conductivity presented by
seawater, the cathodic protection method is extremely appropriate for this condition.
Although it cannot be used to prevent atmospheric corrosion, it is used on the interior
surfaces of water-storage tanks and water-circulating systems.

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4.7. Corrosion maintenance strategy.
A major challenge for maintenance managers is to guarantee that an optimal
maintenance strategy is in place, by proficiently applying available and potentially
scarce resources to maintenance requirements. “Prioritizing maintenance activities is
central to a methodical, structured maintenance approach, in contrast to merely
addressing maintenance issues in reactive, short-term mode.” (Roberge, 2007). The
most critical requirements must be addressed first, before then prioritizing persisting
maintenance needs.
Repair and rehabilitation activities are put in place in order to restore damaged
structures or equipment to their working condition and remedy the problems caused
by corrosion. Maintenance is understood to be a regular and essential activity that
comes with its cost. Nevertheless, corrosion monitoring represents a consequential
part of maintenance and asset management. Four remedial types of maintenance
strategies can be identified, namely corrective maintenance (CM), preventative
maintenance (PM), predictive or condition-based maintenance (PdM or CBM) and
reliability-centered maintenance (RCM).
4.7.1. Corrective Maintenance
Corrective Maintenance can be described as maintenance tasks performed to return an
equipment or structure to its original state. This strategy may refer to maintenance
due to breakdown or maintenance identified by a condition-monitoring program.
Maintenance due to a breakdown can be categorized as planned where equipment
have been allowed to run-to-failure or unplanned maintenance where a breakdown has
occurred due to an ineffective preventative maintenance procedure. According to
Kholy (2006), Maintenance experts have pointed out that there may be a "natural
tendency" to intuitively follow the corrective maintenance approach, even though it
may be (cost) ineffective in ensuring reliability. This maintenance strategy can be
described as a retroactive approach hence why corrosion-monitoring programs do not

Analytical Hierarchy Process applied to maintenance strategy selection for offshore platforms in challenging environments.

Analytical Hierarchy Process applied to maintenance strategy selection for offshore platforms in challenging environments.

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