Life Management of Main Steam and Hot Reheat Piping Systems: Part 2

Abstract

Since there have been several instances of weldment failures in main steam (MS) and hot reheat (HRH) piping systems, most utilities have developed programs to examine their most critical welds. Many utilities select their MS and HRH critical girth welds for examination by consideration of some combination of the ASME B31.1 Code [1] (Code) highest sustained stresses, highest thermal expansion stresses, terminal point locations, and fitting weldments. This paper suggests the use of an alternative life management methodology to prioritize material damage locations based on realistic stresses and applicable damage mechanisms. This methodology is customized to each piping system, considering applicable affects, such as operating history, measured weldment wall thicknesses, observed support anomalies, actual piping thermal displacements, and more realistic time-dependent multiaxial stresses. The high energy piping life consumption (HEPLC) methodology for MS and HRH critical girth welds may be considered as a rational approach to determine critical weldment locations for examinations and to determine appropriate reexamination intervals as a risk-based evaluation technique. The HEPLC methodology has been implemented over the past 15 years to provide more realistic estimates of actual displacements, stresses, and material damage based on the evaluation of field conditions. This HEPLC methodology can be described as having three basic phases: data collection, evaluation, and recommendations. The data collection phase includes obtaining design and post construction piping and supports information. The effects of current piping loads and anomalies are evaluated for potential creep/fatigue damage at the most critical weldments. The top ranked weldments of the HEPLC study are than selected as the highest priority examination locations. The author has completed many HEPLC studies of MS and HRH piping systems. The previous paper (Part 1) provided examples of data collection results and documentation of observed piping system anomalies. This paper will provide examples of evaluation results and recommendations, including a few case histories that have correctly ranked and predicted locations of significant creep/fatigue damage.