1. A REVIEW OF VARIOUS REPAIR TECHNIQUES FOR GAS
TRANSMISSION PIPELINES : ADVANTAGES, LIMITATIONS
AND DEVELOPMENTS
Main author
Rémi BATISSE
GDF SUEZ
FRANCE
IGRC2008@gasunie.nl
Co-author
Stéphane HERTZ-CLEMENS, GDF Suez
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2. CONTEXT
Onshore gas transmission pipelines have a large expansion from the second part of last century
due to the development of natural gas energy and the remote distances between the main
consumption areas and the gas deposit. Nowadays, the mileage of gas transmission pipelines in
the world is more than 1 million of km in the world [CED]. In Europe only, The European Gas
pipeline Incident data Group analysis (EGIG) shows that the onshore network mileage has been
multiplied by more than three times between 1970 and 2004. But in the same time, the failure
frequency of pipelines has been divided by five [EGI]. This result reflects the effort of gas
operators to improve the pipelines integrity using all the chain of management:
• Aggression prevention and detection;
• Inspection;
• Defects analysis;
• Repair techniques.
This paper focuses on repair techniques for onshore gas transmission pipelines exhibiting the
following items :
• Main parameters guiding the choice of repair techniques;
• Review of different types of repair techniques;
• PipeRep, Integrated software for support decision on repair techniques
• Conclusion and Perspective
3. MAIN PARAMETERS GUIDING THE CHOICE OF REPAIR
TECHNIQUES
When a defect is identified to be classified in potential harmful defect for pipeline integrity, the
operators have to make the best choice of repair techniques, the extreme option being the cut
out and replace. The choice must be taken after checking a list of essential parameters
concerning :
• Pipeline geometries and materials;
• Pipeline operating characteristics;
• Pipeline configuration and location;
• Nature and size of defect to repair.
3.1. Pipeline geometries and materials
The pipe diameter is an essential data to select the appropriated external repair by sleeves and
also internal repair which can be only specified for a restricted range of diameter. The pipe
thickness is a limiting parameter for repair techniques requiring welding on pipe as welded
sleeves or weld deposition. The knowledge of steel strength and toughness determine the
residual resistance of the damaged pipe section necessary to quantify the amount of
reinforcement which must be sustained by the repair. Otherwise, the steel grade is a
metallurgical indicator for the repair techniques involving welding which can be limited for high
grade steels more tricky to weld. The presence of girth weld or seamweld in or near the
damaged area can be also a limiting parameter and the welding process have to be known.
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3.2. Pipeline operating characteristics
The repair technique chosen must ensured the full integrity of the pipeline during its remaining
lifetime in operating conditions. The Maximal Allowed Operating Pressure (MAOP) must be
restored after the repair of the damaged section to sustain the pressure fluctuations during the
pipeline lifetime. In consequence, a profile of pressure variation during the time in terms of
amplitude, frequency and mean pressure must be estimated to define the repair of defect. The
specific conditions have also to be taken into account like for example at the exit of
compression station where the temperature can increase up 60°C and affected the durability of
organic materials (composite sleeves) or in opposite at the exit of decompression station where
the temperature can decrease to –40°C and weakened the metallic repair. A pressure drop is
sometimes required during the repair for some techniques. The possibility or not to decrease
temporary the pressure also influences the choice of the repair technique
3.3. Pipeline configuration and location
The pipeline configuration is an other key factor for the choice of the repair method. Additional
stresses due to strong slope or deeply buried pipeline affect the repair techniques which have to
contain more than stresses induced by internal pressure. The presence of bends and elbows
have influence on repair techniques in reason of geometric adaptation and/or induced
supplementary stresses and can exclude certain repair techniques. In other way, the pipeline
location can also exclude a lot of repair techniques for example in urban zone where the pipeline
accessibility in a high density of population area lead for only trenchless repair techniques.
3.4. Nature and size of defect to repair
Obviously, the defect knowledge is essential to choose and to design the repair technique. The
different natures of defects can be classified:
• Corrosion defects, internal or more often external caused by dysfunction of cathodic
protection or/and ineffective external coating;
• Mechanical defects like plain dent, gouge, gouge in dent created by impact with third
party like excavators, different engines for work in progress,...
• Construction defects which are the most often girth welds and seam welds defects like
lacks of penetration, porosities, cracks,...
The orientation (axial or circumferential) and the size determination (length and depth)
generally requires an excavation to size the defect as accurate as possible by None Destructive
Techniques (US, radiography,...).
In December 2000, the European Pipeline Research Group (EPRG) has produced repair
specifications applicable for any kind of permanent repair techniques for natural gas on-shore
pipelines [EPR]. This EPRG method allows a first approach to select the choice of repair
technique candidate without to forget specifications we need. After this approach, the remaining
repair candidates can be evaluated comparing other factors like the cost, the availability or how
easy to bring on field.
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4. REVIEW OF DIFFERENT TYPES OF REPAIR TECHNIQUES
We have to distinguish external repair techniques and internal repair techniques
4.1. External repair techniques
The main external repair techniques are :
• The cut out and replace;
• The bypass;
• The grinding;
• The weld deposition;
• The metallic sleeves;
• The composite sleeve.
•
The cut out and replace is an extreme option. This choice is conservative and safe since
the damaged pipe section is removed and replaced by a sound pipe. However, this solution is
expensive because it requires an interruption of the transit gas in the pipeline to be repaired
involving a loss of earning and could lead to review the contractual requirements with the end-
customers. After the replacement, a new inspection is needed, notably for the girth weld, and
an hydrostatic test can be required before to resume the gas transit.
The main bypass technique is the hot-tap process consisting to bypass the damaged
pipe section. A new pipeline branch surrounding the damaged section is welded on the pipeline
in service. Then, the pressure is applied in the pipeline branch and stopped in the damaged
section which can be cut. So the gas transit interruption is avoided. Nevertheless, certain
conditions are recommended or required as to weld the branch out of girth weld or seamweld.
The branch pipeline with its welds must hold the service pressure. In addition, workmen must
be qualified to weld, and pipe steels easily to weld on field.
The Grinding is a technique used to repair superficial defects removing the harmful stress
concentration effect of defect; hardened material and other damages near the defect like micro-
cracks. However, restrictive conditions are required :
• The operating pressure should be reduced to 80 percent during the repair process;
• Grinding shall not be used as the sole means of permanent repair of dent defect.
• If the crack or the affected material near the defect do not entirely removed by
grinding, an alternative repair technique must be applied instead;
• The removal of all cracks must be verified by NDT after grinding.
• The limits for metal removal for non-indented defects must be in agreement with ASME
B31G [B31] criterion corrosion, and removal by grinding of more than 40 percent of the
nominal wall thickness is not accepted.
Due to this ASME B31G restricted conditions, pipeline operators have qualified their own
optimized grinding methods to increase the application range. For example, GDF Suez has
qualified its optimized grinding by several experimental fatigue and burst tests validated by
Finite Elements analysis using the Dang Van fatigue criteria [DVK]. Figure 1 shows an
example of optimized grinding.
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Figure 1 : Optimized grinding.
The weld deposition (Figure 2) can be applied to rebuild the full wall thickness of pipe
after a metal loss has occurred by corrosion, gouging or after grinding. The weld deposition is
adapted for bend sections or fittings where the use of sleeves is often inhibited. Nevertheless,
the application range of the weld deposition is limited by the burn-through which can occur
when the remaining thickness under the molten weld pool is insufficient to contain the internal
pressure and by the high strength steel microstructures which are susceptible to hydrogen
cracking. The last limit is the need of skilled welders. Detailed guidelines for weld deposition
repairs in the field are given by W.A Bruce [BRU] and in the Appendix B of API 1104 [API].
Figure 2 : Weld deposition
The metallic sleeves are used in two different types of techniques :
• Type A
• Type B
The type A can be installed without welding on the pipe where a defect has to be repair. Two
halves of a cylinder are placed around the pipe. The main advantage of type A is if the flaw
length is less or equal to (20Dt)0,5
where D and t are respectively the diameter and the
thickness pipe, then the sleeve of thickness can be reduced to two thirds of the thickness pipe.
In addition the type A sleeve can be fabricated simply and does not require rigorous non-
destructive inspection. It can be also used for temporary repair (Figure 3). But it can not be
used to repair circumferentially oriented defects and to repair leaking defects. CSA Z662 [CSA]
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provides a guide for the use of steel compression A sleeve to repair longitudinally oriented
crack-like defects.
Figure 3 : Type A metallic sleeve
The type B sleeve (Figure 4) consists of two halves pipes welded together and placed over the
pipe section containing the defect. The ends of the sleeve are welded onto the pipe with full
encirclement fillet welds. If a weld is present on the pipe section to be repaired, the sleeve’s
inner surface can be machined to accommodate the weld. Since the thickness of the sleeve
must be designed to contain the Maximum Allowable Operating Pressure (MAOP), its nominal
thickness value t is determined versus the MAOP, the external pipe diameter, the pipeline
design factor and the Specified Minimum Yield Strength (SMYS) [API]. This type of metallic
sleeve is able to contain the MAOP and axial stresses imposed by secondary loads. So, the type
B sleeve can be used to repair leaks and to reinforced the circumferentially oriented defects.
Figure 4 : Type B sleeve repair
The Composite sleeves have been developed during the last years. GRI (Gas Research
Institute) contributed with a large effort during the 1990s [GR1], [GR2]. A state of the art
assessment of composite systems used to repair transmission pipelines has been provided by
Chris Alexander and Bob Francini [ALX]. The Composite sleeves offer advantages to restore the
full strength of damaged pipelines, to increase the stiffness of the repaired pipe section, to
promote leak before break failure modes and to arrest crack propagation. In addition, the
external corrosion phenomenon is inhibited, the composite acting like an external coating. But
the drawback of composite sleeves is the ageing. The mechanical properties decrease with the
time which is taken into account in the qualification for a permanent repair techniques with a
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lifetime target at least 50 years in the standard specifications [CSA]. The ASME B31.8 [ASM] do
not accept the repair of injurious dents or mechanical damage, “unless proven through reliable
engineering tests and analysis”. Lastly, Chris Alexander and Franz Worth [WOR] have shown
that Dent with gouge removed by grinding could be repaired by Composite sleeves. Two main
techniques are used to elaborate composite wraps for pipeline repair :
• One is based on pre-cured and pre-fitted to standard pipe diameters composite
coils;
• The other, referred as “wet-tape” technology is cured on site.
The pre-cured composite sleeves are made of pre-fitted composite panels which are wrapped on
the section of pipe to be repaired, and hold in place by an adhesive which is placed between the
successive composite layers during application. Due to the elaboration in a factory, the curing of
the matrix is accurately controlled and this process also allows the use of polyester as the
composite matrix which is less sensible to the ageing process compared to epoxies. However,
this process is often not adapted to repair specific pipeline configurations others than straight
and slightly ovalized sections. An example of pre-cured composite sleeve is the Clock-Spring
[CLS], (Figure 5)
Figure 5 : Clock-Spring
For the “wet-tape” technology, the impregnation of the fiber reinforcement is performed on site
during the implementation of the repair. The advantage is that the final composite wrap can be
designed according to the severity of the defect to repair. However, the performances of “wet-
tape” are more sensitive to implementation conditions during the on-site impregnation of the
fibers like the control of the volume fraction of reinforcement and the accuracy of its
homogeneity. The 3X Engineering product (Figure 6) [3XE] is an example of “wet-tape”
composite with the specificity that the reinforcement material is a rope in place of a fiber.
Reinforcement by Rope Polymer Injection
Figure 6 : 3X Engineering Reinforcekit
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From ten years ago, a lot of composite sleeves have appeared on the market in the both
technologies with various specificities, like integration of metallic sheet to be detectable by
inspection, cross fiber orientations to sustain axial stresses, resins no sensitive to humidity to
allow implementation under flooded conditions. More details on these technologies have been
given in the NATO conference [NAT]. The improvement concerning a lot of these technologies is
to know with more accuracy their performance on long term due to the ageing. It’s why, the
PRCI (Pipeline Research Council International) has recently launched a tests campaign on long
performance in realistic conditions of several manufactures of composite repair with SES (Stress
Engineering Services) as contractor [PRC].
4.2. Internal Repair Techniques
Internal repair techniques are trenchless techniques consisting to introduce an internal liner in
the damaged section pipe to reinforce it. These techniques are relevant in urban areas reducing
the annoyance of residents, the traffic obstruction, the damage to the environment and
minimising the time of repair. Unfortunately, lot of them are restricted in range application for
gas distribution or for low pressure below 20 bar. Nevertheless, more and more manufacturers
of internal repair develop technologies for higher pressure application. We can mention the
“Starline-HPL [STA], produced by Karl Weiss Technologies. Starline-HPL is a composite liner
made up of polyester fibers impregnated by polyurethane or polyethylene resin. The
implementation can cover up 600 meters length in trenchless condition (Figure 7).
Figure 7: Implementation of Starline-HPL in urban area (USA)
Starline-HPL was awarded by the German DVGW VP404 certificate [DVG] in 2002 for a
Maximum Allowable Operating Pressure of 30 bar. It has been used for bridging corrosion pits
up to 50 mm (2”) in diameter or to reinforce damaged section containing cracks or defects in
girth weld. An other technology is the SmartPipe technology [SMA] which is able to sustain high
pressure (above 50 bar) and to cover over 500 ft (150 meters) in one trenchless operation. But
the originality of Smartpipe is the fiber optic sensors embedded in the liner constituent a
monitoring system able to detect impact on the pipeline area closed to the repair and leak. The
diameter pipeline reduction due to the thickness of internal liner is compensated by the slick
inner surface of the liner avoiding an increase of the loss of gas flow.
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5. PIPEREP, INTEGRATED SOFTWARE FOR SUPPORT DECISION
ON REPAIR TECHNIQUES
The non-exhaustive review of repair techniques presented in the previous paragraph showed
that several repair techniques are available and each of them has its specific application range.
The choice of the most adapted and suitable repair for a given defect found is not easy and
immediate. It’s why GDF Suez has developed an integrated software called PipeRep [PIP] aimed
to provide a rapid and efficient answer. Versus the input of pipeline and defect characteristics,
the PipeRep software indicates if the defect is repairable or not and advises on the most suitable
repair techniques in case of repairable defect. Currently, the software takes into account the
optimized grinding, the weld deposition and the external reinforcement sleeves which are repair
techniques validated by internal studies of GDF Suez associating laboratory tests and numerical
simulations. Figure 8 shows the software interface for input data.
Figure 8 : PipeRep software Interface
In addition, these repair techniques have been also validated for the assessment of fatigue
resistance due to the variation of gas pressure. So, the PipeRep software is able to precise if
the chosen repair technique for a given defect can be considered as permanent or temporary
(see Figure 9)
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Figure 9 : PipeRep software result. In this case, the most suitable is Clock-Spring.
Defect sizes limit for temporary repair (red curve); for permanent repair (blue curve)
This software is periodically updated considering the repair procedures adaptation and new
repair technologies.
6. CONCLUSION AND PERSPECTIVE
This paper exhibit a lot of available repair techniques. The challenge for gas operators is to
choose the most suitable repair technique for a given defect associated with the pipeline
characteristics. In consequence, procedures and software have been recently developed to
guide the choice. A lot of external composite sleeve repair techniques are appeared on the
market. A knowledge improvement on long term performance associated with installation
conditions is yet needed. There is also an expansion of trenchless internal repair techniques
which should be more and more required due the urban extension around old gas transmission
pipelines.
The validation of all techniques repair should be updated for the emerging pipelines in high
strength grades like X80 and X100. In other way, studies should selected the repair techniques
for the pipelines used for mixture hydrogen-natural gas or pure hydrogen gas, as the future
energetic vector due to the specific interaction of hydrogen with materials. Some pre-studies
have already been done in the frame of the European project called “Naturalhy” [NA1], [NA2],
[NA3].
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7. REFERENCES
[ASM] “Gas Transmission and Distribution piping Systems”, American Society of
Mechanical Engineers, ASME B31.8, New York, ASME B31.8, Edition 2003.
[ALX] “State of the art Assessment of Composite Systems used to Repair Transmission
Pipelines”, C. Alexander and B. Francini, 6th
International Pipeline Conference,
Calgary, Canada, IPC2006-10484, September 2006.
[API] “Welding Pipelines and Related Facilities”, API STD 1104, 19th
Edition, American
Petroleum Institute, Washington D.C., October 31, 2001.
[B31] “Determining remaining Strength of Corroded Pipelines: Supplement to B31 Code
Pressure Piping”, ASME B31G, 1991.
[BRU] “Guidelines for Weld Deposition Repair on Pipelines”, W.A. Bruce, American Gas
Association, Arlington, VA, Catalog N°L51782.
[CSA] “Oil and Gas Pipeline Systems”, Canadian Standards Association, Mississauga,
Ontario, June 2003.
[CED] “Planned Gas Pipelines around the World”, M.F. Chabrelie, CEDIGAZ, February
1995.
[CLS] Clock-Spring, www.clock-spring.com
[DVG] “Rehabilitation von Gas-Hochdruckleitungen mit Gewebeschläuchen im
Druckbereich über 4 bar to 30 bar“, DVGW VP 404,
www.dvgw.de/service/neuerscheinungen2005.htlm
[DVK] “Biaxial high cycle Fatigue tests on a gas transmission pipeline steel”, R. Batisse, H.
Di Fant-Jaeckels, F. Curie and J.M. Virely, Fatigue Fracture Engineering Material
Structures, Vol 19, N° 10, pp 1231-1238
[EGI] “6th
Report of European Gas Pipeline Incident Data Group”, 6th
EGIG-Report 1970-
2004, Gas pipeline Incidents, December 2005 - http://www.EGIG.nl
[EPR] “State-of the-art on existing repair techniques for damaged pipelines” V. Diaz, M.
Zarea, S. Torun and P. Riou, on behalf of EPRG workshop “fitness for purpose”, 27
december 2000.
[GR1] “Long-term Reliability of Gas Pipeline Repairs by Reinforced Composites”, C.J.
Kuhlman, U.S. Lindholm, D.R. Stephen, T.J. Kilinski and R.B. Francini, Final Report
to the Gas Research Institute, Chicago, IL, GRI-95/0071, December 1995.
[GR2] “Field Validation of composite Repair of Gas Transmission Pipelines”, D.R. Stephen
and T.J. Kilinski, Final Report to the Gas Research Institute, Chicago, IL, GRI-
98/0032, April 1998.
[NA1] “Sensitive Analysis of Metallic Sleeve Repair for Defected Pipelines to Hydrogen Gas
Effect on Burst Pressure”, N. Kilic and E. Dur, IGDAS, Naturalhy-WP4 project,
deliverable D35, April 2008
[NA2] “Sensitivity Analysis of Clock-Spring Repair to Hydrogen gas – Effect on Burst
Pressure”, M. Bailleul and R. Batisse, Gaz de France, Naturalhy-WP4 project,
deliverable D35, 7 January 2007.
[NA3] “Weld Repair of hydrogen Charged X52”, H. Wortel, TNO, Naturalhy-WP4 project,
27 december 2007.
[NAT] “Review of Gas transmission Pipeline Repair Methods”, R. Batisse, Safety, Reliability
and Risks Associated with Water, Oil and Gas Pipelines, 2008, Springer.
[PIP] “PipeRep Software : A decision Support tool for the repair of Pipelines”, E. Chateau,
S. Hertz-Clemens, C. Barre, 6th
International Pipeline Conference, Calgary,
Canada, IPC2006-10139, September 2006.
[PRC] “Program to Evaluate the Long-term Performance of Composite Repair Systems”,
MATR-3.4 PRCI project, started in 2008.
[SMA] SmartPipe Company, www.smart-pipe.com
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[STA] Karl Weiss Technologies, www.starlinett.com
[WOR] “Assessing the use of Composite Materials in Repairing Mechanical Damage in
Transmission Pipelines”, C. Alexander and B. Franz Worth, 6th
International
Pipeline Conference, Calgary, Canada, IPC2006-10482, September 2006.
[3XE] 3X Engineering, www.3xengineering.com
