Session: MF-05-02 Fitness-For-Service and Failure Assessment

Paper Number: 85728

85728 - Technical Justification to Extend Girth Weld Examination Intervals 

        The American Society of Mechanical Engineers (ASME) Power Piping Code B31.1 discusses operation and maintenance piping system program requirements in Chapter VII.  These program requirements for covered piping systems (CPS) operating in the creep range include the process of piping system walkdowns and the evaluation of significant field anomalies.

        Piping system walkdowns frequently reveal piping support issues such as bottomed-out, topped-out, or broken spring hangers (Cohn, M.J., Gialdini, R.J., and Nye, O.B., 2021).  Immediate corrective actions for these supports may include adjustments, repairs, or replacements. 

        In addition, the ASME B31.1-2020 Code states that significant displacement variations from the expected design displacements shall be considered to assess the piping system’s integrity.  For example, if the pipe is designed to displace 25 mm downward from off-line to on-line and the field observation is 3 mm downward from cold to hot, the pipe stresses and strains could be substantially different than predicted in the design analysis.  Several examples of malfunctioning supports resulting in significantly different piping system stresses are provided in this document.

        The assessment of the piping system integrity for malfunctioning supports includes determining the highest ranked locations of consumed creep life and implementing applicable nondestructive examinations (NDE) at the selected locations.  Consideration of the actual pipe wall thicknesses and evaluation of the piping system historical operating temperatures and pressures can improve the remaining creep life estimates.

        After evaluations of the site-specific NDE results, the Intertek strategy is to select locations with estimated remaining creep rupture lives less than 20 years for NDE during the next scheduled outage. Locations with estimated remaining creep rupture lives between 20 and 50 years are medium priority ranking during the next scheduled outage, depending on accessibility and available resources.  Locations with estimated remaining creep rupture lives beyond 50 years can have much longer reexamination intervals.  The process of 1) comprehensive piping system walkdowns, 2) simulation as-found stress analyses to observed field displacements, 3) NDE at the minimum remaining creep life locations, and 4) determining the next set of minimum creep life locations has been used to evaluate the current piping system integrity and provide additional confidence in safely operating the piping system until the next scheduled outage.

        Several case studies are discussed to illustrate the piping system integrity evaluation process.  This strategy typically identifies a few critical girth welds to be examined during the next scheduled outage and provides justification to delay near term reexamination of girth welds with estimated remaining creep rupture lives beyond 50 years.

Presenting Author: Marvin Cohn Intertek

Presenting Author Biography: Marvin Cohn is the director of HEP at Intertek-AIM. Over the past 40 years, Mr. Cohn has written more than 170 reports and published more than 60 technical papers, including 8 professional journal papers. Many of these technical papers regarding high energy piping systems subject to creep/fatigue damage have discussed the process of detailed and well-characterized data gathering, simulation of existing field conditions, evaluation of applicable creep/fatigue stresses, creep rupture life consumption in base material and weldments, and ranking of the most critical examination locations. <br/>Throughout the past 25 years, he has participated in the American Society of Mechanical Engineers (ASME) Pressure Vessel and Piping Conferences where he has presented papers, developed and chaired technical sessions, and edited Proceedings. During the last 20 years, he has also actively participated in the ASME B31.1 Power Piping Code Committee. He has particularly contributed to the ASME B31.1 recommended guidelines for post-construction power piping activities. <br/>Mr. Cohn has professional engineering licenses in the United States and Canada. Mr. Cohn is also an ASME Fellow.

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