Analysis of the Causes for the Formation of Fatigue Cracks in Welded Pipes.

Included in this study are an examination of the effect of the asymmetry of fatigue loading on the fatigue strength of welded joints in steel St37 and St52; an analysis of the effect of the shape of the weld and of weld defects, the type of electrode (EA146 and EB146), the welding method (automatic submerged-arc welding, manual arc welding with coated electrodes, welding in CO//2) and of the welding position on fatigue strength; an analysis of the reasons for the formation of cracks in welded joints in a gas pipeline of 508 mm in diameter (wall thickness 8 mm) made of a low-carbon steel of type 18G2 with increased strength; metallographic, chemical and radiographic analysis of the welds in the pipeline; and measurement of weld hardness. It was found that the cracks are caused by notches present at the transition of the weld into the parent metal. Methods of increasing the fatigue strength of joints in the pipeline are given.