This paper will provide data of pressure related ruptures due to interacting threats on pipelines that were operating below 30% SMYS. Specifically the paper will focus on pipelines that ruptured while operating less than 20% SMYS and the broader discussion will consider areas of technology that the integrity assessment
industry may want to focus on to address issues that may affect local distribution companies more than interstate natural gas operators. The paper will also discuss the types of interaction that caused the ruptures and provide a high level decision tree that will allow an operator to begin to address how to model their system to determine if they may have these same threat combinations.
The authors were aware of several ruptures that occurred at low to moderate stress levels within the previous 5 years. This awareness prompted a review of the Pipeline and Hazardous Material Safety Administrations (PHMSA) database for gas transmission, and hazardous liquid transmission pipeline reportable incidents, and also of a database of over 750 examinations of pipeline service failures, hydrostatic test failures, burst test, and other material investigation conducted by Kiefner & Associates
, Inc. (Kiefner) since 1990.
Each case identified in the Kiefner database was checked against the PHMSA reportable incident database for hazardous liquids, gas transmission, and gas distribution going back to 1986. Many are not listed in the PHMSA incident data, in some cases for appropriate reasons. Many incidents occurred in gathering lines and might not have been reportable at the time. Hydrotests or lab burst test are not reportable incidents. One service failure occurred in Mexico, also not reportable. In some cases it is not clear why they are not listed in the PHMSA incident data. In general the data shows that:
- The rate of occurrence of ruptures at low stress is under-represented in the PHMSA reportable incident database
- The reportable incident database does not provide data and incident investigation material that in accessible or visible enough to be used to see paradigm breaking trends that could identify new threats or interacting threats.
- Ruptures at low stress, except perhaps for burnt metal conditions in lap welded pipe, usually have contributing factors.
Specifically, the analysis of the Kiefner data showed there were 7 pipeline ruptures that occurred in service while operating at a pressure below 20% Specified Minimum Yield Stress (SMYS), of which 5 were associated with select seam weld corrosion of electric resistance welded pipe (ERW) and, of those, 4 were low frequency ERW and 1 was a high frequency ERW. These incidents will be discussed in greater detail in this paper. It is not the intent of the authors to suggest that a low-stress rupture could be present that they do not need to be considered in an operator’s distribution integrity management program (DIMP) or transmission integrity management plan (TIMP). This paper will provide a high level decision tree that will allow an operator to contemplate how to model their system to determine if they may have applicable integrity threat conditions.