1986 Volume 4 Issue 1 Pages 148-154
In order to make sound welds free from defects like weld cracking, characteristics of residual stresses around nozzle welds were experimentally investigated in an as welded condition for a thick-wall reactor vessel and an accompanying heat exchanger utilized in a petroleum refining process or a coal liquefaction process.
The residual stresses were measured throughout the thickness of the weldments by applying the measuring methods that had been newly developed for axisymmetrical stress distributions by the authors.
The main results obtained for set-in type nozzle, set-on type nozzle and simple butt welds of pipes are summarized as follows.
(1) Stress parallel to the weld line-The stress indicates the same distribution in the thickness direction regardless of the joints. That is, the maximum value appears just behind the final layer of welds and with descending to the initial layer it decreases. The stress gradient, however, differs from one joint to another, depending on the self-restraint intensity of the joint. Moreover, the peak value of simple butt welds of pipes is about 100 MPa smaller than the others.
(2) Stress perpendicular to the weld line-It indicates the similar distribution as the stress parallel to the weld line. The maximum value in the set-in type nozzle changes from 400 MPa to 600 MPa with the decrease in the diameter of welds from 600 mm to 300 mm. As for the set-on type nozzle, it reaches almost the same level due to the existence of channel as a stress raiser. The stress for the simple butt welds of pipes, however, indicates much smaller value of about 245 MPa and further the same order of tensile stress occurs in the inner surface as well as just behind the final layer of welds in the outer side.
(3) The stress in the thikness direction shows the distribution where the maximum value appears in the center portion of the thickness and it is a low stress level of about 150 to 200 MPa, regardless of the joints.