Under-Supported Main Steam Piping: Hanger Load Adjustments, Finite Element Analysis and Effect on Creep Life

Abstract The High Energy Piping (HEP) system is one of the most essential assets of a fossil fueled power station. Welds and piping supports should be inspected at regular intervals to detect progressive damage mechanisms, such as creep. A visual inspection of piping supports, often referred to as a hanger survey, should be undertaken at every major outage in both hot-in-service and cold-out-of-service conditions. Readings should be recorded from the position scales of all spring hangers during every hanger survey. The support condition of a piping system operating within the creep temperature range can change due to creep redistribution. The distribution of bending stress and location of creep damage development in girth welds in a piping system is, largely, controlled by the supports. It is important to maintain records of the support condition and position, so that actions can be taken to improve the support condition and remaining life of a piping system. A case study is presented for a Main Steam (MS) piping system in a coal-fired power station, demonstrating how conducting regular, accurate hanger surveys identified an under-support condition for the piping system and progressive sagging. The hanger survey records informed the decision to adjust spring hanger loads, which reversed the under-support condition. Comparisons are made between hanger surveys and a detailed creep-redistributed Finite Element Analysis (FEA) to show that creep strain can be attributed to the deformation of the piping system. The detailed FEA was also used to quantify remaining creep life change due to the hanger load adjustments. This paper shows how hanger survey records, along with detailed creep-redistributed FEA, can be used to understand the bending stress, creep-redistribution, and remaining creep life of welds within a piping system.