Thickness and multi-axial stress creep rupture criteria of the Type IV component of a ferritic steel weld

Abstract

The paper summarizes previously derived constitutive parameters for temperatures of 575, 590, 600, 620 and 640 8C. Values of the multi-axial stress rupture parameter, #, are reviewed and recorded. This constitutive parameter set is used to determine the thickness of the Type IV material zone (0.7 mm). Values of Type IV multi-axial stress rupture parameter # are determined for a wide range of butt-welded pipe and cross-welded uni-axial specimens, and an interpolation equation is derived in terms of temperatures and stress level. Finally, continuum damage mechanics (CDM) analyses are performed for pipes and cross-welded testpieces, which include a coarse-grained heataffected zone (CG-HAZ). It is shown that the constitutive parameter set, which corresponds to a minimum creep rate ratio of 1/2.5, with respect to the parent material, gives accurate predictions of lifetimes and damage distributions.

CDM predictions of creep damage initiation and growth in ferritic steel weldments in a medium-bore branched pipe under constant pressure at 590° C using a four-material weld model

“…Two different sets of constitutive parameters will be used for 590 • C: firstly, the set used by Hayhurst and Miller [12] which is summarised in Table 2; and, secondly, the set reported by Hayhurst et al [17] which is summarised in Table 3. The origins of the data used to calibrate the constitutive parameters, is now addressed.…”

“…Multiaxial rupture parameter ν: Hayhurst et al [17] have concluded, following studies on a range of components over the temperature range 565-675 • C, that the constant value of ν = 2.8 provides acceptable predictions of observed behaviour.…”

“…Multiaxial rupture parameter ν: with regard to the behaviour of the weld material, Hayhurst et al [17] have based their evaluation on one set of data at 565 • C, and an assumed linear variation with temperature. The gradient has been selected to coincide with a previously assumed temperature variation for parent material.…”

“…For the type IV material Hayhurst et al [17] have shown that the multiaxial stress rupture parameter ν is dependent upon the level of the average effective stress (σ e ) in the structure. They have calibrated ν-values using test results for plane strain uniaxial cross-weld test pieces manufactured from the same material, and values of σ e in the minimum section of the test piece, in the absence of a weld.…”

“…The weld geometry defined by Hayhurst and Miller [12] will be used in conjunction with two sets of constitutive parameters. The first set is that used by Hayhurst and Miller [12], and the second set has been derived by Hayhurst et al [17], from a study of welded pipes and cross-weld test pieces, for which detailed experimental results are available.…”