Warren R. True
Pipeline/Gas Processing Editor
The U.S. agency that oversees pipeline safety has taken the unusual step of waiving certain natural-gas pipeline maintenance regulations and permitted a group of gas-pipeline operators to perform repairs with a patented composite wrap formerly used only on liquids lines.
The Department of Transportation's Research & Special Programs Administration (RSPA) issued the waivers in April for the Clock Spring composite wrap produced by Clock Spring Co., Houston. The waivers are subject to conditions and to future performance evaluations.
The waivers refer to two sections of the federal code governing natural-gas pipeline repair and replacement and were requested in a filing with RSPA by the Interstate Natural Gas Association of America (Ingaa) on behalf of 29 pipeline operating companies.
These companies agreed to use the wrap according to conditions and restrictions of the waivers.
The wrap is made of polyester resin reinforced by glass filament. On installation, it is tightly wound and adhesively bonded to damaged pipe (Fig. 1).
In its Federal Register notice, RSPA said that the waivers advance use of a new technology and provide an opportunity to evaluate the performance of the wrap under various operating conditions.
What was waived
In its Nov. 22, 1993, filing, Ingaa requested RSPA to waive the safety standards in 49 CFR 192.713(a) and 192.485 for gas transmission lines operating at 40% or greater of specified minimum yield strength (SMYS). The request specified Clock Spring composite wrap.
Section 192.713 limits the only available repair methods to a full-encirclement, welded steel split sleeve over the damaged pipe area or to replacement of the damaged section.
Section 192.485 requires replacement of transmission line pipe that is generally corroded to the extent that wall thickness is unsafe, unless operating pressure is reduced appropriately. If the area of corrosion is small, pipe repair may be effected.
Requests for waivers from the requirements of both standards specified Clock Spring wrap as an alternative to repair large areas of general corrosion or loss of wall thickness.
RSPA says data collected during the initial 3-year waiver period will form a basis to change safety standards that, in certain instances before the waiver, prohibited such a wrap in pipeline repair. The waiver will continue in effect, says RSPA, if initial evaluations are favorable.
Over the initial 2 years, the Gas Research Institute (GRI), Chicago, is assisting operators in data collection and evaluation of the wrap in a statistical sampling of sites, recording the results, and providing those results to RSPA.
GRI's participation, says RSPA, will add uniformity and reliability to evaluations that might otherwise vary among operators. Any operator unwilling to cooperate with GRI in the data collection may not apply the waiver to its pipeline.
The wrap has been subject to a similar, more restricted waiver of Part 192.713 in an earlier field trial conducted by Panhandle Eastern Pipe Line, Houston.
The company wanted to use the Clock Spring wrap to repair six locations on its 24-in. Line No. 2 in Fayette County, Ohio.
That waiver was granted in Mar. 15, 1993; the locations were excavated and the wrap installed in July and August 1993.
Panhandle Eastern agreed to install the wrap according to procedures described in its petition to RSPA, to perform inspections, and to report any instance and cause of the wrap failing.
Those sections of pipe were instrumented and monitored every 6 months following installation by technicians from Battelle Laboratories, Columbus, Ohio, and were excavated in August for evaluation.
Although no detailed results have been made generally available, Clock Spring says the wrap appeared in perfect condition. In the more recent program, operators will conform to the Panhandle waiver restrictions with a few exceptions.
Those include coordinating the composite wrap installations with GRI and within 2 years excavate and evaluate a statistical sampling of sites, record results, and turn over those results to RSPA upon request.
Further, operators are to report any wrap repairs to RSPA within 30 days of repair, use personnel to install the wrap who have been trained and certified by the Clock Spring Co., and record installations of the wrap.
Development
The technology of glass composite reinforcement for pressure vessel and piping applications was pioneered by NCF Industries Inc., Long Beach, in the early 1970s, according to technical meeting presentations by the company in the late 1980s and early 1990s. Initial use was for pressure vessel and piping applications.
The technology proved effective, NCF stated, for slip-on crack arrestors on CO2 pipelines, for lightweight compressed natural gas cylinders for vehicles, and for fire fighters breathing-apparatus cylinders.
Product development by NCF during this period was carried out in cooperation with PPG Industries Inc., Pittsburgh. Clock Spring Co. was formed and exclusively licensed by NCF in 1993.
GRI became involved in 1985 in development of this particular composite material's use for pipeline repair when it funded research and development at NCF Industries. NCF founder Norman C. Fawley had invented the concept of composite wrap as a crack arrestor.
Since 1991 in the U.S., the wrap has been allowed to reinforce petroleum liquids pipelines.
Clock Spring Co. says more than 9,000 units are installed in every major oil and gas pipeline region of the world. The largest line is a 48-in. gas pipeline in Slovakia. No reports have come back of the wrap failing in service (Fig. 2).
What is it?
The composite wrap consists of a sheet of composite which is cured as a continuous, 12-in. wide strip wound in a spiral. The finished product appears and behaves much as would a large spring of an old fashioned watchhence the name. Different lengths of strips are used for diameters from 6 to 56 in. (Fig. 3).
The composite consists of an isophthalic polyester resin and an E-glass. These are the same components with which fiber glass underground petroleum storage tanks have been constructed.
The mechanical strength comes, according to the company, from continuous and parallel glass fibers that run the length of the strip. When the device is being placed onto the pipe, these fibers are aligned circumferentially to it.
Upon installation, each unit has eight concentric layers, each 0.06-in. thick. After installation, the wrap will be nominally 0.5 in. thick over the surface of the pipe.
During repair for wall loss due to corrosion or gouging, the individual layers are bonded to each other with a proprietary, patented, fast-curing two-part adhesive to form, upon curing, a monolithic unit.
The system also includes a high compressive strength, proprietary, two part, load-transferring material that fills between the initial layer and the pipe.
Curing normally takes 2 hr, the resulting repair being stronger than the original pipe when it was new, says the company. It cites hydrostatic and pneumatic burst tests conducted by independent laboratories and supervised by GRI as evidence of the unit's strength.
In one test of an 8-in. OD pipe with an 13.0 x 2.0 in. defect that had penetrated more than 60% through the pipe wall, the test piece failed outside the repair unit wrap at more than 240% of the maximum allowable operating pressure (MAOP).
The intimacy with which the wrap adheres to the surface of the damaged pipe and the load-transferring quality of the filler material are cited by the company as major reasons this system is superior to conventional split-sleeve repair.
In that technique, gaps between the original pipe and the repair steel sleeve are inevitable and can provide opportunities for moisture to build up later. Then there are potential problems created by welding onto an in-service pipeline and by possible weld flaws.
Additionally, the sleeve can interfere with the cathodic protection of the original pipe.
According to the company, the wrap and its adhesive and filler components take on much of the load of the operating pipeline's full internal pressure. And because of the 100% adhesion to the pipe's surface, no moisture can reach the pipe's damaged surface.
Further, the company states that tests of segments repaired with the wrap have indicated continuous cathodic protection.
Savings
The other major difference between conventional sleeve repairing of pipeline and Clock Spring wrap has to do with cost both in money and time (Fig. 4).
Three U.S. pipeline operating companies, which declined to be identified, furnished estimates for using conventional steel-sleeve repair and for using the Clock Spring wrap (Table 1) (78953 bytes) (Table 2) (55424 bytes)(Table 3) (60550 bytes).
A Type A steel sleeve uses no circumferential weld; a Type B has its ends closed by circumferential welds.
Table 1 (78953 bytes) shows estimates by a mid-sized independent company whose policy is to install sleeves no shorter than 2 ft. Use of company personnel was assumed along with factors for benefits and overhead. Costs are in 1993 U.S. dollars. Savings were estimated at $644.24.
The pipeline subsidiary of a major U.S. oil company provided estimates for installing a 2-ft B sleeve on a 12-in. pipeline for a general corrosion anomaly. Costs are in 1993 U.S. dollars. Savings were estimated at $2,213-3,214.79.
A large U.S. independent pipeline company estimated costs for a scheduled rehabilitation project that involved repair of 35 defects on a 20-in. pipeline. Defects, all caused by corrosion, were discovered by an internal inspection pig in a 50-mile valve section.
For the steel sleeve repair, the company worked a 10-hr maintenance shift without overtime. The crews could normally install a single 20-in. steel sleeve per day. About every fifth installation would take longer than a day.
For installing the composite wraps, the company formed a team consisting of a supervisor and three crews, one for excavation and backfill, one for sandblasting, and one for installation.
By working three or four sites sequentially, crews were able to complete 3-5 sites per day.
Costs are in 1994 U.S. dollars. Estimated savings for the entire project were $57,682.50.
Training
Clock Spring Co. provides the initial operator training required by the DOT. This consists of 1 day of classroom reviews of DOT regulations, B31.4 code, and of installation methods and requirements. This is followed by video demonstrations and then hands-on installations.
Also provided is a more detailed 2-day training for supervisors so that they can train their own company personnel and eliminate repeated training by the vendor. Copyright 1995 Oil & Gas Journal. All Rights Reserved.
