Effect of weld angle on the creep rupture life of ferritic/austenitic dissimilar weld interfaces under remote mode I fracture

Abstract

Dissimilar metal welded structures (DMWs) used extensively in conventional and nuclear power plants can suffer from in-service failures at the dissimilar interface with a much reduced life compared to similar metal weld counterparts at the same operating stress and temperature. This paper evaluates the effect of weld angle on the interface creep failure mode of two-dimensional DMW plates consisting of a ferritic steel P91 and an Inconel 82 filler metal within a finite element (FE) framework. A physical cavity growth damage zone model is developed to describe the damage accumulation at the interface, which naturally takes into account the local mode mixity. The material parameters are calibrated against standard 90 o weld creep rupture data and used to predict the rupture life of DMWs with a range of axial loads and reduced weld angles (75 o , 60 o , 45 o and 30 o). The predicted results match reasonably well with the limited interface failure data for a 45 o weld angle. This work also provides additional evidence and insights regarding the improvement of interface creep rupture life of DMWs in power plant pipelines, in particular: (1) Compared with a 45 o weld angle, a 60 o weld angle is more detrimental to the creep life and should be avoided in actual components-on the contrary, damage tolerance can be promoted by designing and adopting weld angles smaller than 45 o , which can have lives exceeding that of standard 90 o welded components; (2) A weld interface with alternating weld angles/paths is expected to enable a greater fraction of the creep rupture life to be taken up with crack propagation compared with a flat weld interface, which also increases the probability of damage detection; (3) A fully constrained boundary condition is beneficial to the creep rupture life compared with a free boundary condition; (4) For weld angles less than 90 o , the diversion of the crack into the HAZ is less likely compared with a 90 o weld angle. Type IV failure mode through the FGHAZ is also less likely to occur.

Type IV creep crack initiation and propagation in mod.9Cr-1Mo steel welds

“…Creep strength of welded joints in power piping, such as similar and dissimilar metal welds, is a key to confirming structural reliability in long-term operation of USC (ultra-supercritical) power plants using modified 9Cr-1Mo steel (ASME P91). Both Type IV creep failure [1] in similar metal welds and interface failure [2,3] in dissimilar metal welds of P91/Inconel are considered in the design stage and in residual life predictions at high temperatures. Since creep strength reduction in similar metal welds of mod.9Cr-1Mo steel in long-term creep [4] was confirmed experimentally, residual life prediction for Type IV creep failure has been an important theme in Ultra Super Critical (USC) plants after long-term service.…”

Creep damage analysis of mod.9Cr-1Mo steel welds considering void mechanics modeling

“…Creep strength of welded joints, such as similar and dissimilar metal welds, is a key to confirming structural reliability in long-term operation. Both Type IV creep failure [1,2] in similar metal welds J o u r n a l P r e -p r o o f and interface failure [3,4] in dissimilar metal welds of P91/Inconel are considered in the design stage and residual life prediction at high temperatures. Since creep strength reduction in similar metal welds of mod.9Cr-1Mo steel was experimentally confirmed in long-term creep tests [5], residual life predictions for Type IV creep failure have also been an important issue in USC plants during long-term service.…”

A theoretical and computational investigation of mixed mode creep crack growth along an interface

“…In the presence of interfaces, whose fracture properties are weaker than the bulk material, e.g. in dissimilar metal welds (Yamazaki et al 2008;Laha et al 2012;Hu et al 2019), a crack might be forced to grow along an interface, which might lead to mixed mode loading at the crack tip, regardless of the global loading conditions. Mode mixity can influence damage development.…”