PSI - Issue 20

Nikolay I. Golikov / Procedia Structural Integrity 20 (2019) 161–166

162

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Nikolay I. Golikov / Structural Integrity Procedia 00 (2019) 000 – 000

Nomenclature

circumferential residual welding stress, MPa axial residual welding stress, MPa

z

tensile strength, MPa mechanic stress, MPa radius of pipe, mm

σ ts

σ

r

thickness of the pipe wall, mm

t

BM HAZ

base metal

heat-affected zone

KCV impact strength RWS residual welding stress WM weld metal

Also, in the presence of RWS, brittle failure can occur at relatively low loads, as pointed by Vinokurov (1973). Thus, the influence of RWS on the performance of structures operating at low temperatures increases considerably. In the Russian regulatory documentation for critical welded structures operating in cold climates, there are no requirements for the level and distribution of RWS. As a consequence, the residual stress in the field joints of gas pipelines is not monitored and measures to reduce them by post-weld heat treatment methods are not taken. In studies of Golikov and Dmitriev (2012), at these conditions, a high level of tensile RWS is preserved in the circumferential welds of the main gas pipeline after its long-term operation. By Vinukurov and Grigoryants (1984) was showed that the girth welding of cylindrical shells leads to the loss of stability near the girth weld (Fig. 1), i.e. the resulting radial displacements, which lead to a narrowing of the pipe diameter at the welded joint section. As a result, a significant decrease of occurs on the outside of the pipe. The level of reduction depends on the welding conditions, the properties of the metal and the rigidity parameters of the shell. In case of z from the inner side of the cylinder due to bending becomes tensile, but on the metal surface from the outer side is compressive. Thus, the most unfavorable high tensile residual stresses and z may occur on the inner surface of the pipe in the root weld zone, it was proved by Deng and Murakawa (2006).

Fig. 1. Imperfect geometrical shape in the area of the butt joint caused by girth.

Studies have revealed that the distribution of RWS of circumferential butt welds of the pipes has a complex dubious character. Both compressive and tensile RWS are detected on the outer surface of the pipes. Similar results are obtained on the inner surface. According to the authors of Mirzaee-Sisan and Wu (2019), the distribution of RWS of the circumferential butt welds is affected by the heat input of welding, pipe wall thickness, the ratio of pipe radius to its thickness, number of weld passes, environment, preheating, edge preparation, etc. Dong et al. (2016) consider that the field of residual stresses of pipe joints mainly depends on the ratio of the radius to thickness (r/t) of the pipe wall, the heat input of welding, the joint design. When the ratio r/t is more than 20, tensile RWS appears on the interior face of the pipe wall. If r/t is less than 20, compressive RWS occurs on the