PSI - Issue 30

Nikolay I. Golikov et al. / Procedia Structural Integrity 30 (2020) 28–32 Nikolay I. Golikov / Structural Integrity Procedia 00 (2020) 000–000

29

2

on crack growth at fatigue failure. Moreover, in the presence of RWS, a brittle fracture can occur at a relatively low load, as indicated by Vinokurov (1973). Rosenstein (2015) noted the significant role of RWS in the brittle fracture of oil storage tanks. However, in the Russian regulatory documentation, the residual stress of the welded joints has received little attention. Therefore, studies aimed at investigating the influence of RWS on the operation of welded structures are relevant. The results of similar studies are presented by Golikov (2019), where the effect of residual welding stress on the destruction of circumferential welds of sections of the main gas pipeline is investigated. The present work is devoted to the effect of residual welding stress on the crack development in the longitudinal welded joints of an underground gas pipeline operating in permafrost soils.

Nomenclature a

Impact toughness

E

Elongation

HFC High-frequency currents RWS Residual welding stress TS Ultimate tensile strength YS Yield strength σ Stress θ

Distance from longitudinal weld of the pipe

2. Materials and methods Pipe fragments of the main gas pipeline with penetration defects of the welded joint were examined. For the construction of the main gas pipeline, longitudinal electric welded pipes with a diameter of 530 mm and a wall thickness of 7 mm made of 09Mn2Si steel were used (Table 1 and 2). According to technical specifications, the longitudinal (factory) seam is welded with high-frequency currents (HFC). During high-frequency welding, a filler material is not applied: the metal on the edges of the products is heated by HFC passing through it. Afterwards, the compression of the heated parts is performed. At high-frequency welding, the seam width is about 0.2 mm. RWS of the longitudinal welded joint of a pipe was investigated by the X-ray method using portable equipment. This method showed itself well in determining the RWS in the works of Dong et al. (2016), Hemmesi et al. (2016), Launert et al. (2017). The X-ray beam spot was 1×4 mm. To calibrate the X-ray equipment, a free of stress carbon steel reference sample and chrome powder obtained by the electrolytic method were used. Similar equipment was used by Gurova et al. (2017). The experimental accuracy of the stress measurements was 20 MPa.

Table 1. Mechanical properties of the pipe metal.

Mean values

Material

a (V-notch), (J/cm 2 )

YS, ( MPa )

TS, ( MPa )

E, (%)

metal pipes

430…445

535…545

35…39

160…175 at -20° C

Table 2. Chemical composition of the pipe metal based on the results of spectral analysis as well as Russian State Standard GOST 19281-2014 for steel of 09Mn2Si grade.

Chemical composition (%)

Material

C

Si

Mn

Cr

Ni

Cu

Mo

Al

P

S

Fe

0.09 0.1

0.65 0.68 0,50 0,80

1.47 1.49 1,30 1,70

0.03 0.05 ≤ 0.3 0

0.02 0.06 ≤ 0.3 0

0.03 0.04 ≤ 0,0 5

Pipe metal

0.04

0.02

0.01

0.01

Bal.

Steel 0.9%C-2%Mn-1%Si according to Russian State Standard GOST 19281-2014

≤ 0.3 0

≤ 0,0 3

≤ 0,12

-

≤ 0,035

-