An Approach to Engineering Critical Assessment of Assets That Cannot Be Inline Inspected

In this paper, a holistic reliability-based approach was implemented for PG&E facility in response to PHMSA’s NPRM. According to §192.624, two integrity concerns were addressed: (1) failure pressure ratio relative to MAOP; (2) remaining life due to fatigue degradation. A case study was presented, in which the POF of hydrostatic test at 1.5×MAOP and the POF of remaining life less than 300 years were determined through Monte Carlo simulations. The variations of material strength, toughness, crack size, pressure cycle, and fatigue growth rate were taken into account.

Six different types of seam welds were investigated individually, including LF-ERW, HF-ERW, FW, SSAW, SMLS and Total that represents the overall. Crack size and the toughness of seam weld and pipe body were analyzed separately for each seam type. Probability distributions of normalized crack depth and length were established from ILI and in-ditch program. Probability distributions of material strength and toughness were established from the Kiefner mechanical testing database. The comparison of POFs attributed to hydrostatic test and fatigue failures is consistent with seam weld quality, considering crack size, material toughness and pipe manufacturing history.

Up to this point, two parts of the IVP effort shave been accomplished for pilot studies. One is NDE-based inference of design pressure for inadequate documentation and the other is ECA-based integrity assessment for PFP and fatigue life. Continuous progress is under way at PG&E to validate the inputs into the present reliability models, such as NDE inspection of their selected facility, more material testing by destructive and nondestructive methods, 3rdparty review, sensitivity analysis, and risk analysis development. As this approach is refined, additional threats can be incorporated into this framework. Outcomes of the research and application will be communicated with the public once they are available.

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