Life prediction tools for complex expensive components of power plants are of great interest and use in these times of increasing competition between electric utilities and decreasing maintenance budgets. Such tools are available in some instances, such as the BLESS code for headers in fossil power plants, but these tools often have not been widely used by the utilities. The purpose of this paper is to demonstrate the use of this tool on realistic header problems, and to provide examples of its use on two representative headers to analyze ligament cracking. The effects of material, operating conditions and tube penetration pattern are studied, with representative times for crack initiation by oxide notching or creep/fatigue being provided, as well as crack growth times following crack initiation. Relative to steady loaidng, pressure and/or temperature cycling may be detrimental to varying degrees and may even be beneficial in some instances, depending on the type of cycle and the resupective creep and fatigue damage contributions resulting from the cycle. The substitution of P91 for P22 material was found to increase both crack initiation and crack growth lifetimes. Consideration of the many complex variables affecting header lifetime is demonstrated.
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