Present work includes creep analysis of ASTM A 335-Grade P22 welds on the high-temperature-section (superheater/reheater) lower headers of bottom-supported heat-recovery steam generators (HRSG): they may be critical because of the long continued service (175000 hours or twenty years), internal reactions, stress intensification at the end-plug and finned-tube joint to the cylinder respectively. Weld life results from the Italian creep code compare to those predicted by the American standard API 579-1. Classical methods applied on the circumferential weld show consistent Von-Mises equivalent stress with both ASME and Italian pressure formulae’s (for the cylinder wall). Numerical-model stress analysis for the finned-tube tee weld shows results consistent with those on both sides of the intersection (pressure-load condition, linear); it shows instead unacceptable values for thermal-load condition, linear and nonlinear. Creep strain values are generally small for both joints, with rates in the weld metal lower than base’s for the circumferential weld. Analysis considers a strength reduction factor for the welds, disregarding possible residual stresses; it assumes a Norton-Bailey power-law for the creep, experimental data from short duration tests providing the basis for extracting coefficients. API 579-1 (Level 1 through 3) assessment results are consistent with the Italian creep code. Creep lives on the weld are consistent with those on both sides of the intersection, the circumferential weld showing lives longer than 300000 hours.

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