PSI - Issue 20

Mikhail M. Sidorov / Procedia Structural Integrity 20 (2019) 180–184

181

2

Mikhail M. Sidorov / Structural Integrity Procedia 00 (2019) 000 – 000

result of non-uniform heating welding and shrinkage at solidification of metal in a zone of a girth weld of the pipeline there are residual stresses. It is important that the residual stresses were minimal and they were in a zone where there are no concentrators of stresses. Because high residual stresses can become negative factor, accelerating the process formations of cracks in girth welds or resulting in fatigue destruction connection by Zerbst et al. (2014), by Hensel et al. (2008), by Shen et al. (2017). Also a type of stress in the zone of girth weld has an important value. Compressive stresses are considered favourable, because they off-load a superficial layer from the stresses caused by the external loading. This increases fatigue strength of girth weld. And tensile stresses - unfavorable, because they reduce fatigue strength and longevity of girth weld by Golikov and Sidorov (2014) . The residual stresses yet distinguish to direction of shrinkage of pipe during welding. They are a circumferential (directed along weld) and axial (directed athwart axes of weld) by Leggatt (2018). These determinations of residual stresses to direction of action are important for the account of the stress state of wall of trunk pipeline. Exactly they are experimentally set by the different methods of measuring and conduct on them the theoretical estimations of residual stresses after welding by Withers et al. (2018), by Xu et al. (2018), by Wu et al. (2018), by Pereira et al. (2019). Study of distribution of residual stresses in the girth weld of pipelines is a rather laborious process and practically is a separate scientific and technical task. It is not always possible to predict how residual stress fields will be formed after welding. The result depends on steel grade, technological process of welding (heat input welding, welding speeds), temperature of environment, geometrical parameters of pipes. The purpose of this paper is definition distribution of residual stresses in dissimilar thickness girth welds. 2. Materials and methods The Girth weld considered in the current study was made of dissimilar thickness of pipes of low alloyed (0.9%C 2%Mn-1%Si) steel with an outer diameter of 530 mm. The wall thickness of the pipe No. 1 was 8 mm, the pipe No. 2 was 10 mm. The pipes were joined by shielded metal arc welding. The number of passes was three (root, intermediate and cover). Mean values of mechanical properties of the base metal and the weld metal are given in Table 1. Chemical composition the pipe metals based presented in Table 2.

Table 1. Mechanical properties of the base metal and the weld metal

Mean values

Impact strength a , J/cm 2 KCV -20 KCV -60

Material

Yield strength σ T , MPa

Percent elongation δ 0,5 , %

Ultimate tensile strength σ B , MPa

Base metal of the pipe No.1 (wall thickness of 8 mm) Base metal of the pipe No.2 (wall thickness of 10 mm)

463

585

32

152

137

560 486

668 609

27 24

109

41 35

Weld metal Fusion zone

89 55

- 22 Table 2. Chemical composition the pipe metals based on the results of spectral analysis as well as Russian State Standard GOST 19281-2014

Chemical composition, %

Material

C

Si

Mn

Cr

Ni

Al

Mo

P

S

Cu

Fe

Base metal of the pipe No.1 Base metal of the pipe No.2 Steel 0.9%C-2%Mn-1%Si according to Russian State Standard GOST 19281-2014

0.12

0.50

1.41

0.03

0.03

0.03

0.02

-

-

0.03

Bal.

0.10

0.57

1.31

0.12

0.12

0.03

0.02

-

-

0.20

Bal.

≤0 .12

0.5-0.8

1.30-1.70 ≤0 .30

≤0 .30

-

-

≤0 .03 ≤0 .04

≤0 .30

Bal.