Creep rates of heat-affected zone of grade 91 pipe welds as determined by stress-relaxation test

Abstract

Cross-weld creep testing conducted at 650 • C under 69 MPa stress has reproduced either the Type I or Type IV failure mode in Grade 91 welds, depending on the post-weld heat treatment procedures. Welds post-weld heat treated below the A C1 temperature have ruptured in the Type VI failure mode, while welds heat-treated above the A C1 temperature of the alloy have ruptured in the Type I failure mode. Heat-treatments at lower temperatures and shorter durations have produced a reduced creep rate. The accelerated short term stress-relaxation test has been conducted to obtain the input creep rates for a finite element model for the cross-weld creep testing. The model predicted secondary creep rates are in good agreement with the results from the conventional cross-weld creep tests. From the finite element model, the creep damage by cavitation is believed to start at regions where the first principal stress and stress triaxiality concentrate.

Creep Behavior of Welded Ferrite-Pearlite 2 1/4Cr - 1 Mo Steel

“…These steels can undergo creep deformation by a combination of stress and elevated temperature [2], [3], [4], [5]. Since joining in the boiler is usually done by welding, it is gaining the attention of many researchers to study weldment and material for hightemperature application [6], [7], [8], [9]. [10], [11], [12].…”

Effect of Postweld Heat Treatments on Type IV Creep Failure in the Intercritical Heat-Affected Zone of 10% Cr Martensitic Steel Welded with Haynes 282 Filler

“…Thus, Type IV failure in the HAZ of 9-12% Cr martensitic steels should be clarified and remedied to ensure high safety and reliability of the component composed of the DMWs for use under USC or A-USC conditions. However, Type IV cracking in the DMWs is still not clearly understood, although it is reported to be associated with softening of the matrix, formation of Laves phase, coarsening of precipitates, and lack of sufficient precipitates pinning the grain boundaries [16][17][18][19][20].…”

“…Several studies have reported that PWHT is effective in retarding Type IV cracking and increasing creep life of the HAZ of 9-12% Cr martensitic steels [20][21][22][23]. On the other hand, some researchers reported that the creep rupture strength after PWHT is lower than that in the as-welded condition [24][25][26].…”

Prediction of prior austenite grain growth in the heat-affected zone of a martensitic steel during welding

“…Engineering steels, such as modified 9Cr-1Mo-V-Nb (P91) steel, widely used in high temperature piping and steam headers in power plant, have optimised microstructures to enhance their operating performance [1,2,3]. However, thermo-mechanical process (e.g.…”