Residual and assembling stress analyses on fillet welded joints of flange pipes and the fatigue strength prediction

Abstract

Fatigue strength of pipe-to-flange welded joints is affected by residual stress and assembling stress at the weld toe. Using an outer peripheral side fillet welded joint with metal inert gas welding exhibiting a certain degree of flange surface flatness, local stresses were measured through an X-ray diffraction method and a strain gauge method, in a released condition and a condition fastened to a thick plate with bolts. Welding residual stresses were compressive in the axial direction and nearly zero in the circumferential direction. The fastening created tensile stresses in the two directions, exhibiting high stress concentration at the weld toe, and their distributions were simulated through finite element analysis as well. The slope of the fatigue limit line was 5.6 times gentler than that of the Goodman limit line at the elastic region. A fatigue strength prediction method for simple designing was proposed considering the effects of residual and assembling stresses from the fatigue test results, and influences of the flange plane flatness, weld flank angle, pipe diameter and thickness were taken into consideration as well.