The program extended over a decade and considered long-term degradation. Special sections of the program specifically investigated cathodic disbondment and cathodic shielding effects, as these were considered to be potentially deleterious to the integrity of the repair and, by extension, to pipeline safety.
An extensive field validation program was required by the United States Department of Transportation (DOT). This requirement was added to verify the laboratory results and to validate real-world behaviour on actual pipelines. The results were published in the public report GRI 1998-0032. This peer-reviewed report was relied upon by the industry and regulators as the basis of documentation to suggest amended code language for both liquid and natural gas pipeline which was subsequently proposed and adopted in DOT CFR 192 and 195.
The various Gas Research Institute (GRI) reports and specifically this field validation study report have often been cited in technical literature discussing various aspects of the composite repair of pipelines. While this body of technical information is widely considered to be extraordinarily valuable to the industry, these reports covered only one potential composite architecture (a continuous strand e-glass fibre in a polyester resin matrix, cured and sized in terms of circumference and number of layers – a composite “˜sleeve’) and one set of constituent components (adhesive and filler within the repair).
Not all potential technologies will produce similar results. In fact, several composite architectures and components were examined and excluded during the initial GRI program, as unlikely to be able to provide the durability required to be regarded as permanent.
Various components and architectures are commercially offered as composite wraps. Comprehensive field validation studies of these various wraps are not readily identified. Current language within ASME B31-8S and other similar codes does recognise a “˜composite sleeve’ as a permanent repair for various types of defects – “˜composite wraps’ do not currently share this recognition. Recently, reports of poor performance of several “˜composite wrap’ variations has led some industry practitioners to question the technologies involved.
Over two decades have passed since the GRI established the first steering committee of industry experts to design the scope and methods of the investigations. Several hundred thousand Clock Spring repairs have now been made. Units have been installed in scores of countries and in almost all conceivable environmental conditions, including onshore, offshore, subsea, tropical, desert and tundra.
Case study 1
In 1999, subsequent to an in-line inspection (ILI) run, five Clock Spring coils were installed on a 457 mm diameter North American liquid pipeline on one joint of pipe. In 2003, the line was selected for an ILI investigation which utilised newer technology and promised a higher level of resolution than that which was utilised prior to 1999. The operator decided to remove the joint of pipe and investigate.
The investigation found that the repairs were effective in all regards. There was no active corrosion, all repairs were well bonded to the pipe, and the repairs were fully functional and effective.
Case study 2
A corrosion investigation on a 457 mm diameter Middle Eastern offshore oil production riser located an area of extensive metal loss which was externally measured as 56 per cent of the wall thickness at the time of repair installation in 1997.
In 2006, the riser was selected for a shutdown. In connection with this, the repair was selected to be removed to verify all prior information regarding the permanent nature of Clock Spring repairs.
The repair was well bonded to the pipe, so a grinder had to be utilised to completely remove the coil and the filler material for the carrier pipe, which was very difficult and time consuming.
After nine years of offshore marine service, in a hot and humid environment, the metal loss measured the precise same 56 per cent identified at the time of the original repair. The repair was sound, and no concerns were identified.
Conclusion
The US DOT required the GRI to conduct a field validation study to verify the laboratory findings that a Clock Spring was a permanent repair and was at least no less safe than traditional repair methods. This field validation study considered units which had been in service for periods of 2-7 years, while the cases reported above considered units that had been in service for periods as long as 15 years.
The findings were consistent – a properly designed and installed Clock Spring is a repair which permanently restores the serviceability of the pipe, a fact that has been proven and validated by reliable engineering data and analysis.
The architecture utilised and the constituent components selected provide the durability required to achieve permanent and safe pipeline riser and pipework repairs in a multitude of service conditions and environments.
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