Validation & Testing

Extensive testing was conducted in the development of the Clock Spring® repair system.  Highlights of many detailed reports by GRI (now the Gas Technology Institute) are provided below.  Contact a member of the Technical Sales Team for more information.

Long-Term Durability of the Clock Spring(R) System.

• GRI Document Number: GRI-98/0150
• Report Type: Topical Report
• Report Period: 2/97 – 4/98
• Authors: Bruen, J.; Boreman, D.J.
• Publication Date: April 1998

Summary

A monitoring program developed to confirm that the Clock Spring system provides a permanent repair for certain pipeline defects is summarized. In 1995, Gas Research Institute (GRI) initiated the program among those gas transportation companies granted a waiver for the use of Clock Springs on their pipelines. The statistical analysis indicated that for a 50-year service life, with a 95 percentage level of confidence, a 36-unit test program was required. No leaks were found in a two-year test program. The 36-unit monitoring matrix contained new installations, sites with existing field installations, and selected laboratory results for combination of variables to reflect specific levels of water, defect size, and pipeline temperature. This report describes the monitoring and test program which resulted in the confirmation of the permanency of this repair system. Appendix A includes rather poorly reproduced Federal Register excerpts with the grants of waiver which allowed the participating companies to use the Clock Spring, and Appendix B presents the Clock Spring Monitoring Matrix.

 

Engineering Properties of Clock Spring(R) for Repair of Defects in Transmission Pipelines.

• GRI Document Number: GRI-95/0072
• Report Type: Final Report
• Report Period: 5/91 – 12/94
• Authors: Barlo, Thomas J.; Milkovich, Scott M.; Zdunek, Alan D.
• Publication Date: December 1997

Summary

The Clock Spring repair system and other glass-fiber composite and adhesive materials were in this program characterized with regard to their potential for shielding cathodic protection current when exposed to natural soil and gas pipeline cathodic protection environments. Experiments were conducted to measure the changes in physical and electric resistivity of E-glass polyester and E-glass vinyl ester composite materials and MA-440 adhesive when exposed to simulated soil groundwater and cathodic protection environments. Shielding was evaluated by comparing potentials measured beneath Clock Spring with those of the exposed pipe away from the Clock Spring. The findings of this project suggest that shielding of cathodic protection currents by Clock Spring repair system is not likely in typical gas pipeline cathodic protection environments. Moreover, these composite materials have electric resistivities and moisture-absorption characteristics comparable to some more conventional pipeline anti-corrosion coatings. Erosion of the composite at scratches and voids in environments with a pH greater than 10 was not considered to be a threat to the integrity of the composite.

 

Summary of Validation of Clock Spring(R) for Permanent Repair of Pipeline Corrosion Defects.

• GRI Document Number: GRI-98/0227
• Report Type: Topical Report
• Authors: Stephens, Denny R.
• Publication Date: October 1998

Summary

A comprehensive 10-year program of laboratory research, development, and field verification which demonstrated that properly installed Clock Spring(R) is a sound, permanent repair system for non-leaking, blunt defects in ductile high-pressure transmission pipe, is summarized. The Clock Spring enhances safety and reliability of operating pipelines and serves as an alternative to conventional full-encirclement steel sleeves. It allows rapid repair of defects without the replacement and rewelding of the pipe or the installation of split sleeves. Its low cost compared with other repair options, and simplicity of installation can encourage expansion of repair and maintenance programs, improving overall pipeline safety and reliability. The program generated an extensive database of material properties, instrumented defect performance experiments, design stress analyses, and field verification results that demonstrate that properly installed Clock Spring can be expected to last 50 years in service. The details of the program, summarized in this report, are provided in other reports listed as references.

 

Evaluation of Plexus MA440(TM) Adhesive and Typical Pipeline Rehabilitation Coatings for Use with the Clock Spring(R) System.

• GRI Document Number:GRI-98/0151
• Report Type: Topical Report
• Report Period: 11/97 – 4/98
• Authors: Boreman, D.J.; Pogemiller, G.E.
• Publication Date: April 1998

Summary

The Clock Spring system allows repair of pipeline defects without the need for welding and without taking the pipeline out of service to replace the pipe. In this evaluation of the performance of Plexus MA440(TM) adhesive used with the Clock Spring system, the goal was to determine if the adhesive offers stable anti-corrosion protection when used alone or under other anticorrosion coatings, and if it is compatible with other coatings when used as an undercoat. The work confirmed that Plexus MA440 alone is a poor corrosion protection for steel pipes. It is recommended that the adhesive should not be allowed to extend well beyond the edge of the Clock Spring/pipe interface. Where the adhesive does extend from the interface, it should be covered with a compatible corrosion coating to provide adequate protection. The report summarizes the results from cathodic protection disbonding tests performed on the Plexus MA440 alone and in combination with other coatings. The report also includes a final report on previous research on the subject conducted at the Basic Industrial Research Laboratory (BIRL) of Northwestern University under GRI contract 5093-272-2749, and a subcontractor report.

 

Recommended Procedures for Clock Spring(TM) Field Monitoring.

• GRI Document Number: GRI-97/0304
• Report Type: Topical Report
• Report Period: 5/96 – 6/98
• Authors: Boreman, D.J.; Hill, V.L.
• Publication Date: June 1998

 Summary

Since 1987 many gas companies participated in installation of Clock Spring(TM) for repair of gas pipes. Many of the operators also participated in the program under which they agreed to excavate and evaluate a statistical sampling of the installations within two years, to record the results of the evaluation of the technology, and supply the results to the U.S. Department of Transportation Research and Special Programs Administration. Gas Research Institute developed a recommended procedure to facilitate the inspection and recovery of the Clock Spring repair system. The guidelines for visual inspection and recovery of Clock Springs in the field under the monitoring program represent engineering guidelines rather than a rigid scientific protocol. Differences in the repair may be encountered because different companies made the installations with variance in adhesives, placement methods, and other details.

 

Pipeline Operations: DOT Waiver Allows Expanded Use of Clock Spring(R) Pipeline Repair Technology.

• GRI Document Number: GRI-95/0216-0008
• Document Type: Journal Article
• Journal Name: GRID Gas Research Institute Digest
• Publication Date: Summer 1995

Summary

U.S. Department of Transportation (DOT) permitted the use of Clock Spring(R), an advanced pipeline repair technology developed by NCF Industries Inc. and Clock Spring Company LP with support from Gas Research Institute and Panhandle Eastern Corporation. The technology consists of a fiberglass composite-reinforced coil that is wrapped around a pipe defect with a special adhesive. The method not only restores the pipe’s original pressure capabilities, but can also improve its resistance to further structural deterioration, and the repairs can be made while pipeline is operating. The article tells the history of the regulatory events related to the development of this technology, and describes the significant advantages the technology has over other repair methods. Names of contacts for obtaining further information are included.

Evaluation of a Composite System for Repair of Mechanical Damage in Gas Transmission Lines.

• GRI Document Number: GRI-97/0413
• Report Type: Final Report
• Report Period: 1/95 – 12/97
• Authors: Alexander, C.R.; Fowler, J.R.
• Publication Date: December 1998

 Summary

The Clock Spring(R) repair system is a composite technology which is an alternative to using steel sleeves for repairing gas transmission pipelines. This research program focused on studying the performance of Clock Spring as a repair for dents and gouges subject to cyclic pressures. The effects of pipe D/t, cyclic mean pressure, and defect severity were assessed. The fatigue testing indicated that the Clock Spring repair system extends fatigue life for dressed mechanical defects by an order of magnitude over grinding as the sole repair. Lap shear tests were conducted to confirm the strength of the current adhesive, MA440, as well as a new high temperature adhesive (HTA).

Analysis of the lap shear results and bi-axial strain gage data indicate that MA440 has more than sufficient strength and durability. The new HTA performs well at high temperature (180 degrees F), and on the average exceeds the performance of MA440 by 60 percent at room temperature conditions. The report contains numerous color graphs and photographs. The document is presented on the CD-ROM in Adobe Acrobat PDF format. The CD-ROM also contains the Acrobat Reader program.

 

Field Evaluation of Composite Repair of Gas Transmission Pipelines.

• GRI Document Number: GRI-95/0073
• Report Type: Annual Report
• Report Period: 1/94 – 12/94
• Authors: Stephens, D.R.; Kilinski, T.J.
• Publication Date: March 1995

Summary

The second year of multi-year program to validate the performance of Clock Spring composite wraps in gas pipeline service is described. Data generated in 1993 are included for completeness in some areas. Much of the reported work involved installation of the composite repair system at  selected locations in cooperation with gas transmission companies. Sixty-nine installations have been done at 20 sites around the United States, each consisting of at least three composite wraps to be monitored. Three of the sites were instrumented with strain gages and the remainder were uninstrumented field exposure sites. The results collected at the time of the report showed no degradation of the reinforcement wraps, consistent with laboratory predictions. It is planned that beginning in late 1995, Clock Springs from selected sites will be removed for laboratory testing and analysis. Strain versus pressure data will continue to be collected at regular intervals at the instrumented sites. Appendixes to the report contain a description of the data acquisition system and instrumentation, and a field exposure assessment of Clock Springs installed in 1989.

 

Field Validation of Composite Repair of Gas Transmission Pipelines.

• GRI Document Number: GRI-94/0139
• Document Type: Report
• Report Period: 1/93 – 12/93
• Authors: Stephens, D.R.; Kilinski, T.J.
• Publication Date: March 1994

Summary

The first year of a multi-year program to validate the performance of Clock Spring composite wraps in gas pipeline service is described. Much of the work involved installation of the composite repair system in selected locations in cooperation with gas transmission companies. To obtain the broadest possible database on performance of composite reinforcements, both instrumented and uninstrumented Clock Springs were installed. The work also included the removal of earlier installed (in 1989) Clock Springs, and the laboratory analysis for evidence of changes in their properties. The appendix describes the data acquisition system and instrumentation for field monitoring experiments.

 

Long-Term Reliability of Gas Pipeline Repairs by Reinforced Composites.

• GRI Document Number: GRI-95/0071
• Report Type: Final Report
• Report Period: 7/91 – 5/95
• Authors: Kuhlman, Chris J.; Lindholm, U.S.; Stephens, D.R.; Kilinski, T.J.; Francini, R.B.
• Publication Date: December 1995

 Summary

A project in 12/15/98: per Keith Leewis, there is a report on the Clock Spring(TM) technology which is to be recommended to all who inquire about this technology first, because it provides a broader overview of several relevant contracts. It is also less technical than many other reports and is more suitable for the purpose of informing about the technology at large. This report is GRI-98/0227. Spring(TM) composite repair system can be used to safely repair metal loss defects in steel gas pipelines. The work encompassed a variety of interdependent tasks, including laboratory testing of composite and adhesive samples, analysis of Clock Springs removed from service, short-term full-scale burst tests on reinforced pipeline sections, and modeling of the reinforced defects in pipe. Long-term laboratory tests using coupons were conducted to determine a 50-year life design stress for the composite. Analysis of Clock Springs extracted after 3-4 years of service showed that no significant degradation of the overwrap occurred in the field. Burst tests on a wide range of defects identified the types of defects that can be safely reinforced with the composite wrap. The data were also used to validate a mechanistic model. A computerized model, GRIWrap(TM), was developed to determine the range in defect sizes that can be safely reinforced for a given pipe size and grade. Model calculations are based on material properties for the steel pipe and composite overwrap, and the long-term design stress of the reinforcement.

 

Long-Term Reliability of Gas Pipeline Repairs by Reinforced Composites.

• GRI Document Number: GRI-93/0453
• Report Type: Annual Report
• Report Period: 7/92 – 6/93
• Authors: Lindholm, U.S.; Kuhlman, C.J.; Stephens, D.R.; Kilinski, T.J.; Francini, R.B.
• Publication Date: November 1993

 Summary

Second year of a comprehensive program to develop a low-cost, nonintrusive repair system for replacement and rehabilitation of corrosion-induced anomalies and mechanical damage in gas gathering and transmission pipelines is reported. The completed work expanded the existing data base on the application and performance of the Clock Spring system. The repair model for metal loss corrosion was extended to small amounts of plastic deformation, and the data base on mechanical properties under hot/wet conditions was expanded. Testing of vinyl ester/E glass composite was started. Instrumented full-scale pipe tests completed during the current year demonstrated successful reinforcement of a long circumferential defect and a deep pit. Recovery of Clock Spring devices with pipeline service was initiated to evaluate any in-service degradation.

 

GRIWrap(TM) Pipeline Repair Program User Manual–Version 1.0.

• GRI Document Number: GRI-95/0244
• Report Type: Topical Report
• Report Period: 6/91 – 6/95
• Authors: Kuhlman, C.J.; Sharron, T.R.; Lindholm, U.S.; Stephens, D.R.; Francini, R.B.;
• Kilinski, T.J.
• Publication Date: September 1995

 Summary

GRIWrap(TM) is a computer software platform developed for the natural gas pipeline industry to determine the depth and axial length of damaged regions of transmission line pipe that can be effectively and reliably repaired with external reinforcements. The program was developed specifically to quantitatively analyze repairs of corrosion loss and mechanical defects using the Clock Spring(TM) composite repair system. It has the capability of determining the in-service hoop stress in the line pipe and composite overwrap based on the defect geometry, pipe size and steel, and composite mechanical properties. Long-term properties of the composite for input into the model were determined by stress-rupture tests of the composite and its adhesive under worst case, simulated pipeline conditions. Short-term performance of repairs was also verified by instrumented full-scale pipe tests designed to fail in the reinforced area. These studies, and knowledge of the stress-strain behavior of the pipe and composite, were incorporated into the thin shell program. This report is the user manual for the model developed as the computer repair code.

 

Development of Fiberglass Composite Systems for Natural Gas Pipeline Service.

• GRI Document Number: GRI-94/0072
• Report Type: Final Report
• Report Period: 1/87 – 3/94
• Authors: Fawley, Norman C.
• Publication Date: March 1994

Summary

Development and evaluation of fiberglass composite materials and systems for crack arrest, defect repair, pipeline rehabilitation, and fabrication of composite-reinforced natural gas pipeline are described. Three types of composite systems were studied: (1) a non-intrusive system for on-line field repair of corrosion and mechanical damage, (2) line pipe reinforced with filament-wound composite, and (3) low-cost systems suitable for over-the-ditch rehabilitation of long pipe sections. Effort during the reported program concentrated on the frist two areas. A unique fiberglass/polyester device, called Clock Spring(R), was developed and successfully tested both as a means of terminating rapidly propagating cracks and for on-line repair of metal loss defects. Composite reinforced pipe was produced and hydrotested, and subsequently installed in an operating pipeline to evaluate its long-term behavior in pipeline service. Summaries of test results are presented in appendixes.

 

Long-Term Reliability of Gas Pipeline Repairs by Reinforced Composites.

• GRI Document Number: GRI-92/0507
• Report Type: Annual Report
• Report Period: 7/91 – 6/92
• Authors: Parr, C.H.; Kuhlman, C.J.; Roy, S.; Pagalthivarthi, K.; Stephens, D.R.; Kilinski,
• T.J.; Francini, R.B.; Newaz, G.
• Publication Date: March 1993

 Summary

The material testing program on uniaxially reinforced fiberglass composites for low-cost non-intrusive repair of corrosion defects and mechanically induced dents in gas transmission line pipe is discussed.  Fiber/resin composite materials have been widely used in a number of industries for construction of pressure vessels. This study describes full-scale laboratory tests which demonstrated that composite reinforcement is effective in repairing certain types of corrosion defects. Testing under extreme environmental simulations showed promise of long operational lifetime. The work resulted in the development of a system called Clock Spring(TM). This is a glass fiber/resin composite device with a spiral structure similar to a clock spring, with glass fibers aligned circumferentially to maximize the composite strength in that direction. The structure is suitable for the restraint of hoop stresses that exist in high-pressure piping and can be installed as an external reinforcement without cutting the pipe. The composite wrap repair method requires no welding and conforms closely to the shape of the pipe with all possible distortions, allowing the bearing of the work load immediately after repair.

 

Arrest of Propagating Brittle Cracks in Low Toughness Pipe with Clock Spring Reinforcements.

• GRI Document Number: GRI-93/0347
• Report Type: Topical Report
• Report Period: 12/92 – 11/95
• Authors: Block, Norman; Kishel, John; Stephens, Denny R.
• Publication Date: December 1995

Summary

Use of Clock Spring(TM) technology as a commercial crack arrester for high toughness pipe began  in 1987. Research described in this report evaluated a new, higher strength form of Clock Spring  composite, now being used for repair of corrosion defects, as a crack arrester for low toughness  pipe. This material, called direct strand Clock Spring, is about 30% stronger than prewoven tape  materials made in the 1987-1990 period. A high strength methacrylate adhesive adapted for bonding the multiple layers of Clock Spring was also evaluated in the current work. In the program, pneumatic tests of the pipe were conducted at a site in the Mojave Desert. Line pipe pressurized with nitrogen was burst under conditions providing brittle crack initiation, propagation, and arrest. Arrest  of cracks was achieved with five of the fourteen Clock Spring arrester designs used in the program. In-line steel arresters installed downstream of the composite wraps were successful in arresting  fractures that breached the composite in three of five cases. An additional paper, “Analysis and Assessment of Clock Spring for Brittle Fracture Arrest,” is included as an appendix.

 

Clock Spring(R) Reinforcement of Elbow Fittings.

• GRI Document Number: GRI-93/0346
• Authors: Block, Norman; Kishel, John
• Publication Date: August 1993

Summary

The efficacy of reinforcing large diameter elbow fittings with Clock Spring(R) composite to increase allowable internal pressure to yield and rupture was evaluated in the reported research. Clock Spring, the nonintrusive repair system, had been previously evaluated for the repair of metal loss corrosion in pipes, mechanical damage in pipelines, and reinforcement of 8- and 10-inch diameter elbows with machined defects. This work extended the analysis of the mechanical performance of Clock Spring to reinforcement of large diameter, 90-degree elbows. The work included finite element modeling of reinforcement concepts, validation of the model predictions in straight pipe, and hydrostatic burst tests of production elbows. The tests measured the pressure to yield and burst with and without composite reinforcements installed at ambient pressure. The results of the work demonstrated that Clock Spring reinforcements provided significant increases in internal pressure to both yield and burst. Appendixes contain a report on the elastic finite element analysis and a set of hoop and axial stress data.