Design Study of a Superheater Header Subjected to Cyclic and High Temperature Loading Available to Purchase

A typical superheater header in a power station is normally subject to high pressure and high temperature loading. Due to increasing fuel prices, many stations especially gas fired power stations are operated cyclically to increase flexibility and to reduce the running costs. Accordingly, new design of heat recovery steam generators (HRSGs) has been required to undertake cyclic operations. For a base load superheater header, the design life is dominated by material creep properties (time to rupture). However, for a header subjected to two shift cyclic operating conditions, fatigue damage could be increased significantly. Therefore, creep-fatigue interaction should be considered. In this paper, a creep-fatigue design life study of a typical HRSG superheater header has been conducted under various cyclic conditions. Creep stresses for the header are calculated using a reverse design code method, and the creep damage is then obtained based on the time to rupture data. Meanwhile, fatigue calculations are carried out using the methodology given in a new European boiler design code BS EN 12952. The results of creep and fatigue damage obtained are presented in a creep-fatigue interaction diagram shown in ASME III Section NH (former N47 Case) for comparisons. After a brief discussion of the results, a conclusion is drawn.