PSI - Issue 30

Mikhail M. Sidorov et al. / Procedia Structural Integrity 30 (2020) 149–153 Mikhail M. Sidorov, Nikolay N. Golikov and Yuriy N. Saraev / Structural Integrity Procedia 00 (2020) 000–000

151

3

that the chemical composition of the samples studied corresponds to steel made of (0.10%C-2%Mn-1%V-1%Nb 1%Al) (GOST 19281-2014).

Table 2. Chemical composition of the pipe metals - as well as Russian State Standard GOST 19281-2014.

Chemical composition (%)

Material

C

Si

Mn

Cr

Ni

Cu

V

Mo

Al

Nb

Ti

W

Fe

Base metal of the pipe

0.08

0.25

1.60

0.02

0.02

0.02

0.05

0.035

0.03

0.02

0.02 Bal.

0.02

Steel 0.10%C-2%Mn 1%V-1%Nb-1%Al according to Russian State Standard GOST 19281-2014

0.05 0.12

0.020 0.050

0.02 0.06

0.010 0.035

0.08 0.13

0.15 0.35

1.60 1.80

-

≤ 0.30

≤ 0.30

≤ 0.30

-

The results of mechanical tests and spectral analysis were obtained using an equipment of the Shared core facilities of the Federal Research Center ‘Yakutsk Science Center of the Siberian Branch of the Russian Academy of Sciences’. UIT was carried out on a special technological complex. It consisted of an ultrasonic generator UZGT 0.5/27 and an ultrasonic impact tool BOMBUS at the inner side of the pipe wall. Sidorov et al. (2010) described the method in detail. Each surface area was treated twice at different speeds and, as a result, with different performance (Table 3). Residual stresses at the outer and inner sides of the girth weld were measured after each treatment.

Table 3. Parameters of the UIT process.

Treatment time, speed and power

UIT-1

UIT-2

Treated surface area

30 s

30 s

Section (60 mm long and 40 mm wide) symmetrically to the weld axis

0.12 m/min

0.06 m/min

420 W

420 W

Residual stress fields in the girth weld were determined by X-ray method according to Withers et al. (2001). Stresses were measured in the axial ( σ z ) and circumferential ( σ  ) direction relatively to the pipe axis at points located at different distances from the weld center (the maximum distance was 20 mm). Before measurements, the tested surface was cleaned, manual grinded, and etched to a depth of 200  m with a mixture of concentrated nitric and hydrochloric acid in a ratio of 1:3 to remove the deformed layer. 3. Results and discussion Fig. 1 shows the results of measurements of residual stresses in the girth weld of a pipe with a diameter of 530 mm at the outer and inner sides before treatment. According to the results of research, it is shown that the outer side of the girth weld after welding mainly compressive residual stresses are formed in the circumferential and axial directions (see Fig. 1 а ). High tensile stresses are observed in the inner side of the girth weld and reach up to 300 MPa (see Fig. 1b). This can be explained by the fact that during pipe welding, there is a strong squeeze in the zone of the girth weld. This leads to the formation of high tensile stresses in the inner side of the pipe wall and mainly compressive stresses on the outer side in the weld and heat-affected zone. Fig. 2 shows redistribution of residual stresses at the inner side of the girth weld of pipe after the first UIT. The levels of axial and circumferential tensile stresses are partially reduced after the first UIT of the girth weld of pipe at the inner side. However, the axial stresses remained at the tensile level in the range of 3-150 MPa (see Fig. 2). A complete transformation of tensile residual stresses into compressive ones, as well as an increase in the level of compressive residual stresses obtained after the first treatment, occurred after the second UIT (see Fig. 3).