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Over the course of the past 20 years, methods have been developed for assessing the probability and root cause of bolted joint leakage based on sound engineering assessment techniques. Those methods were incorporated, in part, into ASME PCC-1-2010 Appendix O [7] and provide the only published standard method for establishing bolted joint assembly bolt load. As detailed in previous papers, the method can also be used for troubleshooting joint leakage. This paper addresses a series of actual joint leakage cases, outlines the analysis performed to determine root cause of failure and the actions taken to successfully eliminate future incidents of failure (lessons learned).

Impact test exemption curves in ASME B31.3 [1] were adopted from ASME Section VIII Division 1 (VIII-1) [2] with subtle modifications. The VIII-1 exemption curves were generated based on early fracture mechanics methodologies and limited amount of test data with an assumption on maximum applied stress intended to correspond to the typical VIII-1 allowable stress criteria. The applicability of the exemption curves for low temperature applications of ASME B31.3 piping (such as blowdown events) is open to discussion because of potentially high longitudinal thermal expansion stresses that may exceed the VIII-1 allowable stress criteria. Additionally, unlike in VIII-1 and ASME Section VIII Division 2 (VIII-2) [3], there is no post weld heat treatment (PWHT) credit on Minimum Design Metal Temperature (MDMT) in ASME B31.3. Detailed fracture mechanics analyses have shown that PWHT can significantly reduce the risk of brittle fracture failures due to its relaxation effect on weld residual stresses, a major crack driving force. In this paper, a fracture mechanics-based methodology for establishing Minimum Allowable Temperatures (MAT) for low temperature applications of ASME B31.3 piping is presented. A state-of-the-art fracture mechanics methodology published in Welding Research Council (WRC) Bulletin 562 [4] is used to develop step-by-step Level 1 and Level 2 procedures for establishing MAT for low temperature applications of ASME B31.3 piping. For the Level 1 methodology, MAT screening curves are developed based on a likely conservative assumption that the stresses in the piping component are at the maximum code allowable stresses in both the hoop and longitudinal directions. For the Level 2 methodology, stress ratio verses temperature reduction curves are developed to consider the effect of lower operating stresses. Similar to VIII-2 [3] toughness exemption curves, the screening curves are generated for both As-Welded and PWHT conditions. The curves can also be used for impact tested materials. The established MAT can be directly coupled to different reference flaw sizes and integrated with an inspection criteria for piping components. Two examples of establishing MAT using both the proposed Level 1 and Level 2 methodologies are presented herein.

A consortium of companies is collaborating in a Joint Industry Project (JIP) for Acoustic Induced Vibration (AIV). Laboratory testing is one of the work areas of the JIP. The goals of the tests are to evaluate typical pipe fittings for AIV induced fatigue, to rank order their AIV risk and to obtain data for validation of computational models. An NPS6x8 (6R8) pressure safety valve was the flow and noise input to a 10S piping system, which consisted of an NPS12 tailpipe input into an NPS12x20 tee. Small bore connectors (SBCs) were included in both the NPS12 tailpipe and the NPS20 header. The type of fitting used as the connection between the SBC and the pipe was varied. The system was operating in a Carucci-Mueller acoustic power of around 175 dB. Vibration acceleration response of the system was measured, and dynamic strain data was also gathered to evaluate fatigue life. The piping and data acquisition system setup will be discussed along with the type of results that are being obtained.