Life Assessment of Hot Reheat Steam Pipe

Abstract

A methodology for assessing the remaining life of hot reheat steam pipe with longitudinal flaws, such as those typically associated with the longitudinal seam welds, has been developed. The approach uses three levels of analysis. Level 1 employs handbook data, assumed flaw sizes, and design parameters. Level 2 employs handbook data, assumed flaw sizes, and actual operating parameters. Level 3 is tailored to a specific case and uses measured data, inspection results, and actual operating parameters. A computer code was developed to apply this approach to hot reheat steam pipe of 2-1/4Cr-1Mo and 1-1/4Cr-1/2Mo-Si steel. Using data from an EPRI survey (RP2596-7), the results of Level 1 analysis were found to predict the potential for creep damage and fracture and to correlate well with past experience, whereas the traditional lower-bound Larson-Miller approach was generally overly optimistic in predicting remaining service life. The approach predicts creep-crack-growth life and assesses the potential of rapid, unstable fracture occurring before a significant amount of leaking takes place. The usefulness of the methodology is illustrated by means of example analyses of a typical cases that might be expected in service. The parameters that were varied in these analyses include type of material (base metal or weld metal), pressure, temperature, pipe wall thickness, and initial flaw size. The approach provides a preliminary tool to help make inspection, operating, and replacement decisions; but additional work is required to validate it as a general tool.