Development and Evaluation of a Steel-composite Hybrid Composite Repair System

Composite materials are widely recognized as a resource for repairing damaged pipelines. The fibers in conventional composite repair systems typically incorporate E-glass and carbon materials. To provide greater levels of reinforcement a system was developed that incorporates steel half shells and an E-glass composite repair system. In comparison with other competing composite technologies, the hybrid system has a significant capacity to reduce strain in corroded pipeline to a level that has not been seen previously. Specifically, the hybrid system was used to reinforce a pipe sample having 75% corrosion subjected to cyclic pressure at 36% SMYS. This sample cycled 767,816 times before a leak failure developed. Furthermore, recent testing has demonstrated that the hybrid system actually places the pipeline in compression during installation. This paper will provide results on a series of specifically-designed tests to evaluate the performance of the hybrid system and the implications in relation to the service of actual pipelines. INTRODUCTION The purpose of this paper is to provide information on a testing program conducted by Stress Engineering Services, Inc. (SES) for Western Specialties in evaluating the ComposiSleeveTM system in repairing and reinforcing damaged high pressure transmission pipelines. This repair system is a hybrid design that integrates steel half-shells combined with a water-activated urethane E-glass composite. The approach used to evaluate the repair system is based on fullscale experimentation, where defects were machined into test samples. The performance of the system was evaluated by means of destructive testing. Much of this work is based on previous studies conducted by SES for the pipeline industry in evaluating competing composite repair technologies. Having access to data associated with these prior studies permits a direct comparison of the repair system with other composite repair technologies. Of particular interest is the level of reinforcement provided by the repair system to the damaged region of the pipe. Composite technologies that are most effective are those systems that are able to successfully reduce strain in the damaged region (i.e. corrosion and dents) to acceptable levels. As will be presented in this report, the repair system is effective in reducing strain in the corroded region of a pipeline significantly below industry norms. In turn, the 767,816 cycles to failure measured for the pressure cycle fatigue sample is greater than any composite repair system tested to date. This paper has been organized to provide the reader with a brief background on the repair system, including a descriptive schematic of the system. A detailed discussion on the test program, including results, is presented. The primary means for evaluating the repair system is its ability to provide reinforcement to a 75% deep corrosion defect machined in a 12.75-inch x 0.375-inch, Grade X42 pipe sample. Sections of this paper include Background (with details on the repair of corrosion), Testing Methods and Results, Additional Testing: Methods and Results, Discussion, and Closing Comments. BACKGROUND The ComposiSleeveTM system is a hybrid design that integrates steel half-shells combined with an E-glass composite having a wateractivated urethane resin system. Unlike conventional composite repair systems that utilize fibers (i.e. typically E-glass and carbon as the primary means for reinforcement), the repair system relies on the stiffness of steel and adhesive bonding between the outer surface of the pipe and inner surface of the steel half shell. Most of the composite repair systems currently on the market are either in compliance or seeking compliance with standards such as ASME PCC-2, Repair of Pressure Equipment and Piping, Part 4, Nonmetallic and Bonded Repairs. These standards were written primarily for wet wrap systems involving the use of either saturation in the field or pre-impregnated resins. Systems involving either precured coils or half shell designs are not explicitly addressed in the current standards. As a result, any evaluation of these systems must rely on assessments via full-scale testing performance and not rely explicitly on calculations to determine the minimum required reinforcing thickness. Provided in Figure 1 is a schematic diagram showing the components of the ComposiSleeveTM system. The variables of interest include selection of the load transfer material, thickness of the steel, selection of the bonding adhesive between the pipe and steel sleeves, and thickness of the E-glass composite material. At the present time there is no single published methodology that can be used to determine the minimum required thickness for a composite-based reinforcing sleeve such as the ComposiSleeveTM system; however, as a minimum, the following should be considered from a performance standpoint. • Stresses must be reduced in the damaged section of pipe to an acceptable level. • Stresses in the reinforcing materials of the ComposiSleeveTM (steel, composite, and adhesive) must not exceed design stresses. • The repair must be able to withstand both static and cyclic pressure loading. • Long-term performance is an essential variable of interest in qualifying repair systems.