L51437 Reaction Stresses and Contractions in Girth Welds

The stresses and deformations associated with circumferential welding of pipes and cylinders can affect the integrity of the joint during construction and its corrosion resistance afterwards. Hydrogen-induced cracking of partially completed girth welds is exacerbated by high levels of stress. Material degradation due to stress corrosion cracking also occurs more readily with greater stresses. The stresses can either be residual or those due to external loading. The extent of stresses caused by welding are also required when engineering critical assessments are conducted to determine the significance of defects in joints. In all cases, it is desirable to reduce the stresses as much as possible. A research program was undertaken to study the contractions and stresses resulting from girth welds made on 616 mm and 914 mm diameter pipes. Measurements were made both during and after welding to determine the effects of welding procedure on pipe deformations and resultant residual strains. The contraction behavior of pipes due to girth welding was examined for two pipe diameters. Welds were made to join pipes whose lengths were at least meters apiece. The welding procedure was changed through the experimental work by using either two or three welders. The theoretical and experimental studies conducted to date in which the heat input and welding parameters were variables have all used a single arc. The results described in this report investigate changes in welding procedures with multiple arcs, and are representative of procedures used to make girth welds in transmission pipelines.