BACKGROUND

The gas pipeline industry that includes interstate, intrastate and local distribution companies (LDC's ) (i.e. the utility) were dealt a bad hand, which means that this could handicap them in the area of pipeline safety and integrity. Unlike liquid lines, most gas pipelines, approximately 66 %, are not smart piggable. Therefore, this places gas pipelines at a disadvantage to monitor with in-line inspection devices. There are many reasons for this situation; however, the primary ones are that they carry one product i.e. natural gas and were not initially designed for pigging. Therefore, there was no need to accommodate pigs in order to separate products.

To overcome this deficit, the Natural Gas Industry (INGAA, AGA & Others) sponsored and conducted many studies that included work from Battelle, Hartford Steam & Boiler, etc. to look for and resolve gaps in the current DOT Regulations on PL Safety. Eighteen individual studies were conducted in conjunction with the OPS concerning the multiple threats encountered by pipelines. These threats are now addressed within the ASME B318 Supplement document for Pipeline Integrity Management. However, for the purpose of this paper, we will focus primarily on Time Dependent type threats, which include external corrosion, internal corrosion and stress corrosion cracking. National Association of Corrosion Engineers (NACE) is playing a very important role in preparation of the first External Corrosion Direct Assessment Standard Recommend Practice in this series relating to integrity management. Cooperation between standards writing organizations was a must for this to happen.

The ASME B31.8 Supplemental for Integrity Management of gas pipelines is a systematic, comprehensive, and integrated approach to proactively counter all twenty-two threats to pipeline integrity as outlined within this overarching standard. It specifies pressure testing, in-line inspection (ILI), direct assessment or new technologies to verify the integrity of a buried pipeline. It provides guidance for the interval between periodic integrity evaluations.

The majority of natural gas transmission pipelines cannot accommodate ILI tools, nor can they be taken out of service for pressure testing to find time-dependent defects, such external or internal corrosion or stress corrosion cracking. Direct Assessment methodologies provide alternative means for assessing the integrity of such buried pipelines.

Direct Assessment is a process through which an operator is required to integrate data on and knowledge of the inspection records, physical characteristics and operating history of a pipeline, with the results of diagnostic testing performed on the pipeline system to determine the state of integrity of the subject pipeline. Excavating, to directly touch and examine the pipeline verifying that the conditions predicted by the integration of the knowledge, validates the process and diagnostic testing results are actually found when the pipe is exposed.

The Direct Assessment methodologies for external, internal and stress corrosion cracking provide the four C's:

• Comprehensive methodology in a NACE standard which encourages the use of a

• Consistent integration of historic records and current inspections applying

• Conservative engineering estimates to ensure

• Continuous improvement through performance measurement and feedback.

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