Impact of Plate Thickness and Joint Geometry on Residual Stresses in 347H Stainless Steel Welds

Abstract

Weldments of 347H stainless steel are potentially susceptible to stress relaxation cracking at elevated service temperatures. Mitigation of stress relaxation cracking susceptibility within a multipass weld requires a good understanding of welding practices and manufacturing techniques to control high tensile residual stresses. In this work, the dependence of residual stress distribution in 347H stainless steel on base plate thickness, joint geometry design, and preheating condition was systematically investigated by using three-dimensional finite element models. The finite element models were validated through good agreement between neutron diffraction measurements and calculated elastic strains. The single-V-groove welds with and without a preheating step all produced similar peak von Mises residual stresses, above 450 MPa, within both the fusion zone and heat-affected zone (HAZ). In plates thicker than 0.5 in. (12.7 mm), high tensile residual stress could be observed in a relatively large area, from the middle of the plate thickness to underneath the top surface. A double-V groove shifted the high tensile stress area to the middle thickness of the weld. A single-J-groove weld was able to confine the residual stress to a very small region near the middle thickness within the fusion zone and suppressed the von Mises residual stress within the HAZ to below 400 MPa.

Failure Analysis for Molten Salt Thermal Energy Storage Tanks for In-Service CSP Plants

“…It also exhibits good sensitization resistance due to the addition of Niobium (Nb) that favors the formation of carbonitride (C,N) precipitates [25,26]. However, several issues have been reported in SS 347H welds made with matching E347 filler including SRC in the fusion zone (FZ) or heat-affected zone (HAZ) during service or even during post-weld heat treatment (PWHT) [3,25,[27][28][29]. Creep and SRC mechanisms are intrinsically related during floor welding fabrication.…”

“…(2) at 600°C-1,050°C (in red) from Colorado School of Mines thermo-mechanical testing, which used a Gleeble machine for the microstructure of the HAZ of SS 347H [3,55]; and (3) at 100°C-400°C (in gray), from the National Institute for Materials Science (NIMS) data sheets [56]. Note that the material database used for SS 347H and the finite element weld modeling method used in this work were validated through neutron diffraction measurement [3].…”

“…(2) at 600°C-1,050°C (in red) from Colorado School of Mines thermo-mechanical testing, which used a Gleeble machine for the microstructure of the HAZ of SS 347H [3,55]; and (3) at 100°C-400°C (in gray), from the National Institute for Materials Science (NIMS) data sheets [56]. Note that the material database used for SS 347H and the finite element weld modeling method used in this work were validated through neutron diffraction measurement [3]. 3D finite element models using the sequentially coupled thermo-elastic-plastic method were established to systematically investigate the dependence of residual stress distribution in SS 347H on base plate thickness, joint geometry design, and pre-heating condition [3].…”

“…Note that the material database used for SS 347H and the finite element weld modeling method used in this work were validated through neutron diffraction measurement [3]. 3D finite element models using the sequentially coupled thermo-elastic-plastic method were established to systematically investigate the dependence of residual stress distribution in SS 347H on base plate thickness, joint geometry design, and pre-heating condition [3]. The elastic strain profiles calculated from the weld model agreed well with those measured from neutron diffraction mapping, which indicates that stress contours calculated from strain evolution from the weld model are reasonably accurate.…”

“…Several failures in molten salt hot TES tanks in commercial CSP plants have occurred around the world [1], including the Crescent Dunes Solar Energy Project in the United States, causing significant economic loss and mistrust in this CSP technology. The majority of these failures are associated with the design and fabrication procedures of the tank floor, leading to high residual stresses after welding fabrication, as well as the friction between the floor and the foundation and the temperature gradients in the tank floor that result in high stress (that routinely exceed the SS 347H yield strength) during operation, stress relaxation cracking (SRC), buckling, and creep [2,3]. Technical standards for design, fabrication, and implementation of molten salt tanks operating at temperatures up to 565°C do not exist today.…”