For the past decade there has been relatively wide acceptance in using composite materials to repair damaged has and liquid transmission pipelines. There have been numerous independent research programs performed by pipeline companies, research organizations, and manufacturers that have contributed to the acceptance of composites as a legitimate repair material. Additionally, insights have been gained by both pipeline operators and composite repair manufacturers during field installations. ASME has also responded by adding sections to both the ASME B31.4 and B31.8 pipeline codes, as well as currently developing a repair standard for nonmetallic composite repair systems by the Post Construction Committee.
The purpose of this paper is to provide for the pipeline industry guidelines for using composite repair systems to repair pipelines and what information is needed to properly evaluate how composite materials should be used to repair high pressure pipelines. The contents of the paper will include discussions on what critical elements should be evaluated for each composite system, items of caution and concern, and the importance of evaluation to ensure safe long-term performance.
There were three principal driving forces that led to the interest and investment in composite materials in the United States in the mid-1950s and 1960s: the designer's demand for lower weight and higher rigidity for aero- or space structures, electronics, sports equipment, and other applications; the solid-state theory's predictions of extremely high potential crystal strengths, more than one million psi tensile strengths, and elastic modulii of more than 100 million psi; and the flourishing U.S. economy.
Advanced composites had come of age in the early 1960s with the development of high-modulus whiskers and filaments. While whiskers were easily made, their composites were of poor quality; but the 60 million modulus boron filaments reinforcing epoxy were very successful and were used in fighter aircraft and later in sporting goods equipment. As their costs came down over the years, the use of composites has migrated to oil and gas applications, including pipeline repair [1].
From a transmission pipeline standpoint, Clock Spring® (System A) is recognized as the first composite repair system that was widely used to repair pipelines. In 1991 the Gas Research Institute (GRI) initiated a research program at Southwest Research Institute (San Antonio, Texas) and Battelle Columbus Division (Columbus, Ohio) to thoroughly test a composite repair system that had been developed by industry. Over the next five years an intense research effort was carried out to assess the performance of System A that utilized an Eglass/polyester material and methacrylate adhesive.
In order to use composite materials to repair transmission pipelines, the Office of Pipeline Safety (OPS) required the use of waivers before installations could take place [2].
First, OPS granted the Panhandle Eastern Corporation a waiver of § 192.713(a) to install System A over six corrosion anomalies on Line #2 in Ohio, subject to certain monitoring and reporting conditions (58 FR 13823; March 15, 1993).
