Hope this helps PPM on Power Plant GAs & Steam Turbines

1. An Ounce of Prevention is Better Than a Pound of
Cure!
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Steam
Verses
Gas Turbine

2. An Ounce of Prevention is Better Than a Pound of
Cure!
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HVAC
Case Study

3. An Ounce of Prevention is Better Than a Pound of
Cure!
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Contents
● Power
● Whose is this
● Facing Problems
● Understanding the current repair need
● Vendor Selection
● Planning for success
RCM Condition Inspection& Cause Correction
● Paying attention
● Total Quality Management
● Monitoring & Final Inspection

4. An Ounce of Prevention is Better Than a Pound of
Cure!
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Power

5. An Ounce of Prevention is Better Than a Pound of
Cure!
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The power industry has experienced a shift in steam turbine (ST)
maintenance strategies.
two compounding factors have driven the change
The first factor has become the overwhelming task of managing the
maintenance of newer technology
Gas Turbine (GT) related maintenance
These machines by design and operating profile require a greater
frequency of maintenance than their steam turbine predecessors. Frequent
GT inspections and repairs/upgrades have driven maintenance budgets to
a point at which something has to give.
Once well-cared-for work horse of the industry, the steam turbine has
become a maintenance afterthought as funds are reallocated to GT issues
Major ST outage- intervals and inspection points are pushed out to support
the expense and frequency of Gas Turbine inspections, repairs and
upgrades.

6. An Ounce of Prevention is Better Than a Pound of
Cure!
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Whose is this please?
The second issue compounding the problem is a plant asset ownership
turnover.
With uncertain asset ownership longevity it becomes very difficult at the
plant level to justify and gain approval for a major ST outage.
These major outages face costs exceeding £1 million very quickly. It is an
investment in the long term viability of the asset.
In today’s ever changing asset ownership environment, it becomes a very
difficult business case for a maintenance manager to build with the current
owner.

7. An Ounce of Prevention is Better Than a Pound of
Cure!
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Three major steam turbine repair types have become clear as a result of
this shift in maintenance focus.
● Failure Based – Component failure with collateral component
damage, forced outage & repair
● Failure Avoidance Based – Repair need identified & repair planned
at next opportunity
● Planned Reliability Centered Maintenance (RCM) Based – Failure
Mode identified & Risk Mitigation Steps implemented

8. An Ounce of Prevention is Better Than a Pound of
Cure!
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Facing the problems
Many maintenance managers are now faced with the massive task of
developing significant steam turbine repairs plans vs. maintenance plans.
Failure Based repairs can be devastating in nature to the plants overall
viability.
These failures must be avoided at all costs as they force the unit off line
and into an unplanned outage, costing the facility millions in downtime.
Failure Avoidance Based repairs are a step in the right direction, this type
of repair is classified as those that have been identified via inspection
practices and planned for at the next outage.
Planned Reliability Centered Maintenance repairs have simply not had
the focus required to ensure long term reliability of the steam turbine.

9. An Ounce of Prevention is Better Than a Pound of
Cure!
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Understanding the current repair
needs
Top Two Problems the industry faces

10. An Ounce of Prevention is Better Than a Pound of
Cure!
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1. Managing Major Steam Turbine Repairs
● Vendor Capability Qualification
● Repair Planning
● Repair Monitoring & Final Inspection
2. Protecting the Investment, Reliability Centered
Maintenance
● RCM Inspect & Correct
● Case Study
Steam Turbine Repair Management
Steam turbine repair success lies heavily upon planning and parts supplier
communication.
A Request for Quotation (RFQ) should include the requirement of a
facility qualification review, agreed upon in process inspection points & a
final inspection prior to shipment.

11. An Ounce of Prevention is Better Than a Pound of
Cure!
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Steam turbine repairs are categorized into three main groups and should
be managed as individual repair scopes.
1. Rotating Blades
2. Stationary Nozzles & Seals
3. Rotor Forging – Journals & Wheel Sides

12. An Ounce of Prevention is Better Than a Pound of
Cure!
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Vendor Selection – Quality Assurance
● Steam Turbine refurbishment facilities are no longer monopolized by
the OEM. Non OEM options are now available for the customers
consideration,
● How do you decide who is going to perform the repair work?
● Machining capability and vendor quality control must be reviewed for
acceptance against the required repair scope.
It is easy to assume a steam turbine repair center has the necessary
capability and quality control to execute any given repair, it’s not that
simple.

13. An Ounce of Prevention is Better Than a Pound of
Cure!
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● It is recommended that within the Request for Quotation (RFQ), a
facility capability review is required by a qualified member of your
● team or a third party steam turbine manufacturing engineer should be
utilized.
● There are many factors that impact overall facility qualification such
as machine capability, facility load lifting capacity, and most important
vendor quality control.
● Applying the appropriate expertise in evaluating a potential vendor
can be the difference between a successful repair and complete
failure.
Anyone can ask qualification questions, having someone on your team that
understands the capability needs and the answers from potential suppliers
is essential.
Planning for Success – Customer Commitment
Machining cycle is no longer the driving factor in overall repair cycle,
material lead time and production capacity now drives the schedule.

14. An Ounce of Prevention is Better Than a Pound of
Cure!
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There has been a focus in the manufacturing world over the last 15 years
to embrace LEAN Six Sigma manufacturing methodology.
The focus on waste elimination has improved steam turbine blade
machining and overall repair cycles immensely.
Standard machining cycle times have been slashed with the transition from
batch and que machining strategies to single piece flow for steam turbine
blades.
Transition has reduced cycle by eliminating costly set up time, product
scrap and rework costs narrowing in on one blade at a time.
Becoming more common (bar stock is on site as appropriate) enabling
steam turbine blade rows to be manufactured in days vs weeks.
Key to success in the initial stages of the planning is customer commitment
to order (issuing the repair facility a purchase order), enabling the vendor to
secure material and a manufacturing spot for your project.
It is important to note that success lies in the hands of the customer in
these important first steps of the planning process and action should be
taken as soon as practically possible.
Monitoring & Final Inspection

15. An Ounce of Prevention is Better Than a Pound of
Cure!
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As today’s manufacturing facilities drive to improve cycle time and increase
profits, and investments in technology takes the lead.
As machining technology advances and CNC capability improves the need
for skilled machining labor to run the process takes a hit.
This shift leaves quality up to automation as facilities have fewer people to
monitor machining processes and verify final dimensions.
The reason, it is important for the customer to maintain a presence in
the repair process
Essential early identifying of potential gaps in the quality system.

16. An Ounce of Prevention is Better Than a Pound of
Cure!
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It is important to maintain a solid working relationship with your repair
facility.
Consideration must be taken not to interrupt the production rigor in place
while taking the opportunity to add value to the overall process.
Take time to understand the process in which your repair will be subject to
and select opportunities within that process to inspect your repair.
As repair facility management sees your level of process understanding,
you will drive heightened awareness to vendor quality and schedule
response on your project.
Focus your efforts on adding value to the repair process, not distractions or
repeat steps.
Relying completely on the repair vendor to execute the work with no
customer presence leaves the customer susceptible to quality oversights
and production schedule setbacks.
Paying attention

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Cure!
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A customer that pays attention to the repair process, stays informed and
maintains a presence in the process keeps their job at the top of the priority
list for the repair facility. In the initial RFQ it should be clearly spelled out
that the customer requests to monitor the repair cycle at predetermined
points based on the repair type.
As with repair vendor qualification, it is essential to apply the appropriate
expertise to the repair monitoring efforts. Be sure the member of your team
selected to monitor the repair is comfortable with repair procedures, gaging
techniques, tolerance control, turbine design and applicable machining
practices
.
RCM Condition Inspection & Cause Correction

18. An Ounce of Prevention is Better Than a Pound of
Cure!
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Steampath component reliability and overall life cycle will not improve
simply because the unit has been repaired.
Cause correction against the identified failure mode must be acted upon in
order to protect the investment and improve overall reliability.
RCM based repair success starts with sound life cycle management
practices.
The core of which relies upon applying the appropriate level of expertise to
your inspection & monitoring efforts.

19. An Ounce of Prevention is Better Than a Pound of
Cure!
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Embracing the rigor of a RCM program and applying the analysis tools built
to support this system will increase risk management success.
The Failure Modes & Effects Analysis (FMEA) process, when run by an
experienced team,
has proven to add tremendous value to understanding and tracking current
risk levels based on component conditions found.

20. An Ounce of Prevention is Better Than a Pound of
Cure!
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An inspection that simply generates a photo appendix of the as found
steampath condition to compare to the next years photos is of no value in
regards to extending component life cycle and improving reliability.
If you are not inspecting against the known failure modes, their cause and
effects, you are simply just “looking around”, taking pictures and waiting for
a failure.
At best this would be failure avoidance planning. Applying steampath
expertise when borescoping will ensure all failure modes are being
inspected for, identified and analyzed.
Moisture Erosion 1a

21. An Ounce of Prevention is Better Than a Pound of
Cure!
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LP Blading 1b

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An experienced steampath engineer, one with operations and unit
design/function expertise can effectively analyze the effect and cause of all
failure modes, their severity and likelihood to impact unit reliability.
Utilizing the FMEA rigor has proven to increase customer understanding in
the level of risk associated with the findings across the steampath aiding in
repair project justification efforts.
The FMEA process offers an objective expert analysis of the identified
failure modes severity, likelihood of occurrence and ability to detect failure
prior to an impact to unit reliability.
This level of understanding enables the asset owner to make an educated
decision where to invest in reliability for the biggest return on their risk
mitigation investment.
It is important to note that the majority of steam turbine damage is
avoidable and correctable when identified and analyzed in its early stages
correctly.
Adopting a culture of inspect & correct will improve overall component life
cycle and unit reliability.
When steam path damage is found, it is important to understand the root
cause such that corrective operational & maintenance measures can be put
in place to mitigate the risk to reliability.
Failure Mode – LP Blade Moisture Erosion

23. An Ounce of Prevention is Better Than a Pound of
Cure!
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LP blade moisture erosion is a common industry concern gaining increased
visibility as owners are forced to make expensive repair/replacement
decisions
Because as the condition has not been inspected for, monitored or
corrected against.
Earlier mentioned by applying the appropriate expertise if inspection rigor is
in place is crucial to the success of the inspection and correct culture.
Where one inspector may see LP blade entrance side moisture erosion via
borescope (fig 1a) on the entrance side of an LP blade set (fig.1b).
Only to make a note of it year 1 and come back year 2 to find the damage
has become more pronounced.

24. An Ounce of Prevention is Better Than a Pound of
Cure!
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Experienced inspectors who understand the failure mode will offer
suggestions to further analyze the condition and eliminate or reduce the
cause.
In this case, it was recommended an operational data analysis be
performed.
The scope of the analysis was to isolate any operational conditions that
may be enhancing moisture erosion in the back end of the unit.
It was noted that during times of reduced turbine loading LP hood sub
cooling (fig.2) was occurring.
The sub cooled condition has the potential to impact the point within the
LP steampath that the steam temperature drops below saturation and
starts to condense.
LP blade erosion should be expected over the life cycle of a condensing
steam turbine.
Damage severity, however, will vary greatly based on unit operating profile.
It is recommended that the progression of this condition be continually
monitored.
Conducted as part of the scheduled steampath borescope, or LP hood
visual inspections.
Steam turbine design optimizes the ability of the steampath to extract and
convert thermal energy into mechanical rotary motion.
The extraction of thermal energy occurs as the steam drops in pressure,
temperature and expands in volume through the steampath components.
As this thermodynamic shift nears completion in the last stages of the
turbine, steam begins to drop below the saturation line and moisture levels
increase.

25. An Ounce of Prevention is Better Than a Pound of
Cure!
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While it is most efficient to run with dense steam in the back end LP
sections of a condensing turbine, there is a risk associated with dropping
below the saturation line.
Steam that has dropped below the saturation curve and is physically
changed in direction drops moisture out as condensate.
This condensate tends to hang on the trailing edges of stationary blades
subject to being forced off by passing steam.
In this condition the passing steam atomizes the hanging condensate
creating a “pressure washer” effect on the preceding rotating blades at the
entrance side outer perimeter.
The atomized condensate (moisture) impacts the entrance side of the
rotating blades creating a harsh environment of moisture induced erosion.
Moisture erosion is easily identified by the rough and rigid pitting created in
the surface of the blade material. In moderate cases, it is contained to the
entrance side of the blade.

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Cure!
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In severe cases, you will see the exit side thin edge effected as well. These
pits in the face of the material create hundreds of troubling stress risers in
the material which under load can lead to cracking and ultimately blade
failure.
If physical access is available to the blades affected it is a prudent risk
mitigation step to perform a Non Destructive Examination of the blades for
crack propagation.
Access permitting, Array Eddy Current testing has been proven to be the
most effective field testing method that can be applied with the turbine still
in the casing.
Some blades are manufactured with erosion shields designed to quickly
erode in the first years of operation with the intent that the eroded surface
of the shield will protect the underlying turbine blade material.
The design theory is that the shield materials eroded landscape will capture
and retain water droplets within its eroded surface to act as a shield against
further erosion.
It would be important to consult with your OEM or steam path engineer to
verify if your LP blades have steam shields and their recommended action
regarding the level of moisture erosion present.
In today’s market many facilities are forced to run at reduced load, creating
an increased risk of early saturation in the back end if LP hood temperature
is allowed to sub cool.
With less demand on the condenser it is important to adjust hood spray and
cooling water flow to maintain LP hood temperature.
Sub cooled condensers impact the point, within the turbine’s last stages, at
which steam drops below the saturation line. This ultimately encourages
destructive moisture erosion of the LP blades.

27. An Ounce of Prevention is Better Than a Pound of
Cure!
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Figure 2 illustrates the relationship of LP hood temperature and condenser
condensate temperature to a reduced steam turbine load. Initially,
adjustments to condenser cooling water flow and hood spray use are not
made and hood temp plummets.
As adjustments are made to limit hood spray use and condenser cooling
water flow, the LP hood temp recovers, stabilizing the back end steam
conditions of the unit.
Conclusion
While it is possible to minimize the progression of this failure mode by
taking action, inevitably the blades will require replacement as this failure
mode cannot be completely eliminated considering today’s operating
profile.