Natural Gas Pipeline Company of America (NGPL), a subsidiary of Kinder Morgan, Inc., has been monitoring their pipeline system for the presence and severity of stress corrosion cracking (SCC) for more than thirty years. With the identification of near neutral pH SCC (also called low pH SCC) on this system, over the past five years NGPL has implemented a comprehensive SCC integrity management plan (IMP). Through their SCC IMP, NGPL has been finding and eliminating near critical near neutral pH SCC and other defects from their system, while using data from the program to obtain a better understanding of the relationship of SCC to existing pipe and environmental conditions. NGPL transports commercial quality natural gas to the Chicago area through a multi-line system that originates in various North American supply regions. The system right-of-way encompasses most of the American mid-west and crosses many physiographic areas. The pipelines have varying grades, diameters, and wall thicknesses, and were constructed at different times. Overall there are approximately 10,000 miles (16,000 kilometers) of pipeline that fall within the current NGPL SCC IMP. The primary purpose of this paper is to relate some of our experience with SCC on our system and describe the some of the innovative technical aspects of the existing in-house SCC IMP. This paper outlines some historical examples of the NGPL methodology for detecting near neutral pH SCC in pipeline steels using two or more separate pipeline investigation techniques. The basic steps of SCC direct assessment (DA) are described, as well as the process of integrating the predictive SCC model with in-line inspection (ILI) low level analysis signatures to determine the extent and severity of near neutral pH SCC on the NGPL pipeline system.

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