Abstract
In order to clarify the relationship between the reduction of hydrogen concentration through low temperature postweld heat treatment (LTPWHT) and its treating conditions, the analyses on the diffusion of hydrogen during the treatment were carried out using an analytical computer program in which the influence of the gradient of hydrostatic stress caused by welding residual stress distributions was taken into consideration.
As a result, it was found that the ratio of the highest hydrogen concentration at any time during the treatment to the hydrogen concentration at the point right below the final pass of welds just after welding, could be arranged by a parameter (τ+Dptp), where r and Dptp are the parameter of hydrogen diffusion determined from welding conditions and the product obtained by multiplying the diffusion coefficient at a temperature of the postweld heat treatment by its holding time, respectively. The influences of the dimensions of the weld zone, such as plate thickness or groove width, upon its relationship were also clarified.
Moreover, the diffusion coefficient of hydrogen for 2 1/4Cr-1Mo steel weldments, which becomes necessary to determine the conditions of the heat treatment for preventing the cracks, was determined in the temperature range of 150°C through 300°C.
