Life Management of Main Steam and Hot Reheat Piping Systems: Part 1

Abstract

Many utilities choose critical girth welds in their main steam (MS) and hot reheat (HRH) steam piping by consideration of some combination of the ASME B31.1 Code [1] (Code) highest sustained load and thermal expansion stresses, terminal point locations, and fitting weldments subject to stress intensification. As an alternative, a life management methodology is used 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 life management 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. This methodology has been implemented over the past 15 years to provide more realistic estimates of actual displacements, strains, stresses, and material damage based on the evaluation of field conditions. This high energy piping life consumption (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 anomalies are evaluated to prioritize critical examination locations. Results of the examinations at the most critical locations are used to determine the degree of material damage at lead-the-fleet locations. The author has performed many HEPLC studies of MS and HRH piping systems. This paper will provide examples of data collection results and documentation of observed piping system anomalies.