This document summarizes a study evaluating the use of reinforced thermoplastic pipe (RTP) to replace aging offshore pipelines in a mature oil field in a more cost effective manner. Hydraulic modeling showed that RTP generated lower pressure drops than carbon steel pipelines for smaller diameters. An installation cost comparison showed that RTP installation was $2-4 million USD lower cost than other options like flexible pipe and carbon steel. RTP was selected as the best option due to its lower total cost of ownership over the life of the pipeline.

1. OTC-25767-MS
Conceptual Design for Offshore Pipeline Replacement in Mature Field,
Using Reinforced Thermoplastic Pipe for CAPEX optimization in F-Field
Pipeline Repair and Replacement Program
Hanto Yananto, Pertamina Hulu Energi ONWJ, Yuyung Girindra, Pertamina Hulu Energi ONWJ, and Steven
Kennedy, Polyflow Global
Copyright 2015, Offshore Technology Conference
This paper was prepared for presentation at the Offshore Technology Conference held in Houston, Texas, USA, 4–7 May 2015.
This paper was selected for presentation by an OTC program committee following review of information contained in an abstract submitted by the author(s). Contents
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Abstract
A study was initiated to evaluate the benefit of low capital
cost and low maintenance cost technologies to rehabilitate
pipelines in marginal fields and apply artificial lift
solutions to marginal wells to keep them running profitably
and with an attractive return on investment (and with no
sacrifice to safety and environmental risks).
The challenge is to have a new technology with lower
“Total” cost from design, procurement, installation,
operation and maintenance during its life time. In addition,
the technology must meet the required planned production
flow, which, in some cases, can be higher than current
flow.
RTP per API15S was shown as the most cost effective
solution in rehabilitation of pipelines in marginal fields.
Introduction
Offshore North West Java (ONWJ) field has been operated
for more than 40 year and comprises 9 flow-stations and
hundreds of NUI platforms. About 600 pipelines are used
for transporting either fluid or gas. At least 5 pipelines have
to be repaired or replaced due to integrity of aging
facilities. As a mature field, any additional Capex to
maintain base production shall be carefully assessed.
Figures 1 and 2 show examples of “F” field network.
Figure-1 Pipeline Network at F3-F2
Figure-2 Pipeline Network at FS1-FS231-F261
The objective of this paper is to evaluate and select the right
existing pipeline candidates that are suitable for pipe in

2. 2 OTC-25767-MS
pipe pull through method. Success criteria include
acceptable hydraulics which meets line requirements, flow
velocity minimum performance to minimize maintenance
expenses, material selection to eliminate chemical
treatment and capital cost estimates to demonstrate a
beneficial return on investment to ONWJ.
Pipeline Replacement Strategy
The replacement strategies followed by ONWJ are
according to the following steps, i.e.
- To utilize the existing pipeline casing as the conduit for
RTP flow line pull through method.
- RTP flow line will be pulled through from tie-in flange
below Emergency Shutdown (ESD) Valve at one
platform to the same elevation at another designated
platform.
- RTP diameters which meet the hydraulic method and do
not require a modification to existing riser bends are
preferable to those that require riser bends.
- Modifications to bend does not constitute a rejection of
the process. ROI analysis will determine if project is
viable.
- Total installation cost comparison will be generated to
compare technology options.
Design Scope
The assessment effort was limited to a process that will
engage the lower hanger flange (just below the
Emergency Safety Valve) on one platform to the lower
hanger flange of the terminating platform, as in Figure 1
Figure 3. Design Scope
Appraise Stage
In the appraise stage, several technology options were
considered to select the best option to maintain the
pipeline; API 17J Flexible Pipe and API 5S RTP with Pull-
Thru Installation method are the alternative options
compared to traditional rigid carbon steel pipeline..
Commercially Available Pipe Sizing
The new pipeline will be designed to anticipate maximum
fluid or gas production from the existing platform. It is
essential to establish the right size of the pipe for current
and future operating requirements as proper pipe sizing can
minimize the ongoing maintenance by creating critical
velocities to move solids with the liquid flow stream.
One of the benefits of RTP and Flexible pipe systems are
their polymer liners which are smooth extruded surfaces
compared with carbon steel pipe. These smooth liner
surfaces reduce flowing pressure drop for comparable
diameters, thus allowing smaller diameter RTP to replace
larger diameter carbon steel pipe.
References have shown carbon steel to have a relative
roughness of ~ 0.006 in/in versus thermoplastic extruded
relative roughness of ~ 0.00005 in/in. This allows for
smaller diameter polymer lined pipes to create critical
minimum velocities to move solids while not creating
excessive pressure drop.
Modeling was performed to establish the desired diameter
using a polymer lined pipe. Table 1 summarizes the
comparison between new line size and commercially
available existing pipeline size for API 5S, API 17J and
steel pipe. Technical selection was later performed based
on market availability, material capabilities, practicality in
installation, pipeline size and length.
Table-1 Technical Selection Pipeline candidates in F-
Field
Installation Total Cost Comparison
Table 2 shows an installation total cost comparison for the
various technologies assessed. The least cost total
installation cost technology) is RTP per API 15S. Flexible
pipe per API17J is more expensive and carbon steel per
API 5L the most expensive.
 RTP (API15S) ~$2MM USD less than API 17J flexible
 RTP (API15S) ~ $3-4MM USD less than carbon steel
Table-2 Price Comparison of Selected Pipelines in
F-Field
1 F2-FP 6" N/A 2.2 Y Y N/A
2 F3-F2 4" 12" 2.6 Y Y Y
3 F4-F3 6" N/A 0.9 Y Y N/A
4 FP-F62 8" 12" 8.8 Y N/A N/A
5 F62-FP 16" 12" 8.8 Y N/A N/A
6 F62-F3 12" 12" 8.8 Y N/A N/A
7 FS1-F62 16" 16" 8.9 Y N/A N/A
8 F62-FS1 6" 16" 8.9 Y Y Y
9 F11-F3 12" 6" 7.6 Y N/A N/A
10 FS231-FS1 10" 12" 2.6 Y Y N/A
11 FS1-FS231 4" 12" 2.6 Y Y Y
12 F261-FS231 8" 10" 4.4 Y Y N/A
13 FS231-F261 4" 10" 4.4 Y Y Y
14 H2651-F14P 10" 12" 13.1 Y N/A N/A
15 F231-sstH2651 8" 8" 0.2 Y Y N/A
16 F14P-FP 12" 16" 11 Y N/A N/A
Carbon Steel
API 5L
Flexible Pipe
API 17J
RTP
API 15S
No. Pipeline
Existing
Size
New
Size
Length
(KM)

3. OTC-25767-MS 3
Installation Schedule
One additional advantage that flexible pipes have over
carbon steel pipes is in the duration of the installation.
Figure 4 shows a generic “pipe-in-pipe” installation
schedule for RTP per API 15S for pipeline lengths less than
5km.
Figure-4 Generic Installation Schedule
RTP per API15S was seen to offer the least cost total
rehabilitation solution and was then selected best return on
investment for use in marginal fields.
Following is a more detailed discussion of RTP
technology.
Selection of New Pipeline
The new pipeline is proposed to be installed by using
Reinforce Thermoplastic Pipe (RTP). The general
construction of RTP piping system consists of an
internal liner and substructure (either Nylon or PPS) that
is wrapped externally by aramid fibre in order to
increase allowable pressure of polymer pipe.
The PPS liner is recommended due to its low permeation
rates for both CO2 and H2S gasses. The Fortron liner
has a relative roughness friction coefficient of 0.00005
in/in was used which approximately a hundred times less
than the value is used for steel pipe (0.006 in/in).
RTP line will be installed inside of existing carbon steel
pipeline using method called Pull Thru. The existing line
is currently no flow since the platform is inactive now.
The main concern of using this method is the capability
of existing bends in the steel in handling RTP inside
which depend on the size of the RTP used. Bend
modification, if required, will give impact to the ROI
calculation.
Material comparison of RTP and steel pipeline is shown
in Table 3.
Table 3 Material Comparison
Hydraulic simulation of the new pipeline comparing
RTP and carbon steel line is summarized in Table 4.
Table 4 Comparison of hydraulic simulation result using
RTP and Carbon Steel
As shown in Table 4, for 6 inch pipeline, generally RTP
and steel pipeline generate similar pressure drop (only
0.2 psi difference). For 4 inch, pressure drop along the
steel line is higher than pressure drop along RTP, as well
as for 3.5 inch. It shows that for small diameter, the RTP
will generate less pressure drop.
Still shown in Table 4, fluid velocity for RTP is quite
higher than steel line. It minimizes solid deposition as
long as it is still lower than erosional velocity. An
operational cost avoidance benefit of the higher velocity
is the possible elimination of pigging operations.
Another significant cost benefit for RTP is in the
installation process and associated cost. Steel line lay
process requires lay barge, possibly DP2 vessels, which
resulted in high cost installation. RTP system can use
small work barges and utility vessels to transport small
machinery and materials hence the installation cost will
be less expensive.
Table 5 shows options selection by comparing
advantage and disadvantage of various sizes and
material of pipeline.
Table 5 Option Selection
2 F3-F2 4 2.6 7.2 6.6 4
11 FS1-FS231 4 2.6 7.2 6.6 4
13 FS231-F261 4 4.4 10.08 7.7 5.76
Total 24.48 20.9 13.76
CARBON STEEL
API 5L
RTP
API15S
Estimate Cost
(USD x 106
)
FLEXIBLE PIPE
API 17J
Estimate Cost
(USD x 106
)
Estimate Cost
(USD x 106
)
Length
(KM)
No. Pipeline
Size
(Inch)
Day 1 Day2 Day3 Day 4 Day 5 Day 6 Day 7
Vessel Equipment Loading
Vessel Transit to location
Deoil
Scaffolding and Equipment Setup
Actual Lay
Hydro-test
On Production
Line Down x x x
Nominal Size
Pipeline
Resulting
Pressure Drop
(psi)
Landed
Pressure (psi)
Velocity
(ft/s)
Requirement for
bend modification
6” RTP 3.6 671.4 8 Yes
6” Steel 3.4 671.6 5.5 -
4” RTP 24 651 18 No
4” Steel 26 649 12.8 -
3.5” RTP 48 627 24 No
3.5” Steel 50.1 624.9 16.3 -

4. 4 OTC-25767-MS
Generally steel has proven reliability but the installation
cost is very high. On the other side, RTP installation and
operational costs are lower but reliability is unknown
since it has never been implemented on this field.
For similar size, RTP generate less pressure drop than
steel line. Due to that reason, RTP will be more efficient
to be implemented first time in the recommended
options since it is only for gas lift. Six (6) inch size will
be oversized considered the maximum rate is only 3.4
MMSCFD.
The allowable pressure drop along the line should be
about 10-20 psi/mile (6.2-12.4 psi/km). The 3.5” RTP
and steel is resulted in very high pressure drop (48 and
50.1 psi). The only option left is 4” which is technically
and commercially feasible since it is resulted lower
pressure drop (24 psi) and the cost is cheaper than
installing new steel line.
Bend Modification Implications
An additional consideration in pipeline rehabilitation or
conversion of lines to gas lift etc. is whether the existing
bends in the steel casing need to be modified.
This is a critical cost impact item in the Return on
Investment (ROI) calculation – not as important when
production flow is sizeable but very critical for pipe-in-
pipe applications in marginal fields.
The recommended initial applications do not require
modification to existing bends.
RTP Pipeline Data
The line pipe is described as Piping and associated Joining
System pulled inside the existing steel line pipe casing. In
combination, both systems provide a stable flow line
system for the transport of gas/crude or other products.
The existing carbon steel casing does not require the use of
anodes, cathodes or other corrosion inhibitors as a
requirement for further operation as the RTP pipe will
assume all the integrity requirements for flow. This can
result in a significant operation cost avoidance.
By nature, the piping system is inert to hydrocarbons;
except for flange and splice sections which can be coated
(inner tubular) with surface protectant; such as Fortron
Polylphenylene Sulphide (PPS) or other coating, prior to
installation.
Material Selection
The RTP pipe evaluated was constructed with internal liner
of Fortron Polyphenylene Sulfide (PPS), reinforced with
aramid fibers and jacketed with Nylon (refer to Figure 5)
Figure 5: RTP Pipe Construction
The PPS liner was selected because of its resistance to
hydrocarbons and Brine, as well as CO2 and H2S. In
addition, PPS exhibits very low permeation rates for both
H2S and CO2 gas.
Permeation
Permeation through the liner does not necessarily damage
the liner but rather can create operational issues such as
build up gas pressure in the reinforcement layer creating
issues with the outer jacket. In the case of the rehabilitation
of a carbon steel pipeline, a build up of gas in the annulus
between the RTP and the steel pipe can create non desirable
issues.
The Figure 6 is comparing various polymers permeation
rates in CO2 at various temperature to show a side by side
comparisons.
Figure 6 Comparison of Polymer Permeation Rates
Figure 6 shows that polyethylene, a common polymer used
in the oilfield has significant permeation rate compared to
No Option Advantage Disadvantage Cost (USD)
1A 6” Steel
- Reliability is proven - High installation
cost
7,200,000
1B 6” RTP - Low installation cost
- Unknown
reliability
- Bend modification
is needed
N/A
1C
6” Flexible
Pipe
- Reliability is proven
- Low installation cost
- Material is slightly
expensive
6,600,000
2A 4” Steel - Reliability is proven
- High installation
cost
N/A
2B 4” RTP
- Generate less pressure drop
than steel line (for same
size)
- Low installation cost
- No need bend modification
- Pipeline repair if
leak during
operation
- Unknown
reliability
4,000,000
3A 3.5” Steel - Reliability is proven
- High pressure
drop
- High installation
cost
N/A
3B 3.5” RTP
- Generate less pressure drop
than steel line (for same
size)
- Low installation cost
- No need bend modification
- Unknown
reliability
N/A

5. OTC-25767-MS 5
the other engineering plastics and Fortron (PPS) showed
significantly lower levels of permeation.
No Venting Required
Safety is of critical concern for ONWJ. Therfore, it is
preferable to have a pipe-in-pipe system that does not
require venting of the annulus as a consequence of gas
permeation through the RTP wall into the annulus. This
criteria negated the use of polyethylene (PE) based liners
and materials.
PPS liners do not require venting of the annulus.
Typical RTP Installation Method
The first step in installation is to disconnect the
terminations at the lower hanger flange as in Figure 7
(before the safety shut off valve). In some cases due to
limited space the safety valve and associated piping might
be removed to gain acceptable access for pull through.
Figure-7 Typical Lower Hanger Flange Access /
Disconnected Flange
Operational Pigging Philosophy
Once the lower hanger flanges are disconnected, a
gauging pig will be sent through the line with cable
attached to assure that the existing casing has an
acceptable size opening to accept the RTP.
For sending of the gauging/messenger pig, a compressor
is required.
The compressor will be integrated with a temporary
pigging joint “in-line”. Figure 8 gives a visual of this
connector type which is standard in industry. When
messenger process is complete this joint is removed.
The temporary pig launcher will have flange connection
to connect with existing terminations at the platform.
Figure-8 Messenger Pig
Pulling Method
A pulling cone is attached to the RTP pipe. The pulling
cone has holes that allow for water to fill the pipe as it is
pulled within the steel casing. The operator must use a light
weight, high strength rope for the messenger pig and pull
through operation.
A winch and rope should be capable of pulling with greater
than 2x the expected pulling force (which will provide the
operator with a suitable safety factor).
The pull through speed is expected to be 7-14 m/minute.
Speed is monitored via winch controller. A faster pulling
rate is possible when the size of the casing is much larger
than the RTP pipe.
As one RTP spool is completely unwound, the pull is
stopped, the existing empty spool removed and replaced
with a new spool in the unwinding station. Then a splice
coupling is used to join the two pipe sections and continue
spooling.
A custom designed 10,000 psi rated pump is required to
swage the couplings at joining locations. The final issue is
determining the end connections. When possible it is
recommended to flange to the existing steel flange
termination because as the RTP pipe is flexible,
terminating to a non-rigid structure can cause some issues
with excessive bending.
The pipe is then pulled past the lower flange hanger (~ 5-
10 m) and the pipe is cut near the lower flange.
The proprietary termination coupling is then added using
the hydraulic press. Terminations are provided that mate
to the existing flange structure. The termination flange is
then bolted to the lower hanger flange assembly to close
off the pipe in pipe system.
Pre-commissioning

6. 6 OTC-25767-MS
The final installation process step is to hydro-test the line
to ensure splice and termination joint integrity. In general,
the installation contractor will follow the following
recommended hydro testing guidelines for RTP. Typically
the hydro-test is done at 1.5 x the “operating” pressure for
gas lines and 1.25x the operating pressure for liquid lines
of the line for an 8 hour period. However, there are a few
requirements from the RTP Supplier:
1. Pressures testing should be done with liquid (salt water
is acceptable).
2. The line should be increased in 250-500 psi increments
and held for ~15-20 minutes before increasing pressure,
thus allowing the pressure to stabilize. (There is some
stretching of the line and pressure drops can occur
during the pressurization of the line.)
3. Once the final pressure is achieved, there may be a few
recharges required during the pipe relaxation before the
pressure test hold procedures begin.
4. The pressure profile curve is asymptotic, so there may
be slight pressure decay for several hours before the
pressure stabilizes.
Conclusions
During Appraise-Select Stage, 3 pipelines were proposed
to be replaced with RTP by pull through method as shown
in Table 6.
Table 6 Summary of RTP pipeline candidates
Pipeline
Section
Cost Subsea
Work
Pulling
Through*
F3-F2 $ 4 mio No < 1 day
FS1-FS231 $ 4 mio No < 1 day
FS231-F261 $ 5.76 No < 1 days
*) RTP pull-thru equal to sending the messenger wire up to
pulling thru the RTP.
The budget required for capital expenditure on those RTP
pipelines can be optimized to 56% of regular carbon steel
pipeline laying by pipe lay barge as shown on table 7.
Table 7 Summary of CAPEX optimization
Additional operation cost reductions can be acheived from
RTP systems by elimination of pigging operations and
chemical injections associated with carbon steel pipelines.
The following is the summary of selection RTP as the most
valuable for those 3 pipelines.
- Pulling Through method is the most valuable solution
for pipeline rehabilitation in marginal field where there
were suficient existing abandoned pipeline as casing for
RTP pipe.
- No subsea intervention, but might need subsea team
support to be standby during pigging.
- For the selected lines, the maximum size RTP
applicable for existing pipeline as casing without
modification is about 4”, All for gas lift.
Pipeline rehabilitation using RTP technology has the
potential to greatly impact the performance of marginal
fields. Rehabilitation of existing lines can realized ~56+%
less capital cost compared to an installation using
conventional carbon steel pipeline. Proper planning and
analysis of the pipeline to be rehabilitated shall be executed
at earlier stage to ensure smoother installation process and
better achievement to the project in term of schedule and
expenditure spending.
References
- N/A
CAPEX
Optimization
2 F3-F2 4 2.6 7.2 4 56%
11 FS1-FS231 4 2.6 7.2 4 56%
13 FS231-F261 4 4.4 10.08 5.76 57%
Total 24.48 13.76 56%
Length
(KM)
No. Pipeline
Size
(Inch)
Estimate Cost
(USD x 106
)
RTP API15S
to CS API5L
CARBON STEEL
API 5L
RTP
API15S
Estimate Cost
(USD x 106
)