PSI - Issue 30

Igor Sannikov et al. / Procedia Structural Integrity 30 (2020) 144–148 Igor Sannikov et al. / Structu al Integrity Procedia 00 (2020) 000–000

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Fig. 1. Fragments of pipes with diameters of 529 mm cut from sections of the main gas pipeline

The mechanical properties of the base metal and welded joint are determined by static tension according to the methods of GOST 10006-80 and GOST 6996-66. The static tension of the samples was performed on a Zwick / Roell Z600E universal electromechanical testing machine. The average value of tensile strength, yield strength, and relative elongation is determined by averaging three samples. Impact bending tests of the samples were performed according to the methods of GOST 9454-78 and GOST 6996-66 using the Amsler RKP 450 pendulum impact-testing machine. The impact energy of the pendulum was 300 J. The samples were cooled in the Lauda RP 890 climate chamber to the temperature of minus 70 and minus 20 °C. The average impact strength was determined by averaging three samples. Samples for impact bending of the base metal of pipes No. 2, No. 3.1, and No. 3.2 were cut perpendicular to the pipe axis and subjected to straightening by a static load. Samples of the field welded joint were cut in the direction of the axis of the pipes. The thickness of the samples of the welded joint was reduced to 7 mm, which is the thickness of a thinner side, by machining. When testing welded joints, concentrators were applied along the weld metal (WM) and the fusion line (FL) according to GOST 6996-66. Moreover, the samples were subjected to preliminary chemical etching to determine the application site of the concentrator. 3. Results and discussion In the design documentation for the Taas-Tumus-Yakutsk main gas pipeline, various grades of steel and the corresponding pipe lots are specified. The spectral analysis of the pipe samples was accomplished to compare them with the certificate data. The factory certificates of pipe lots similar to them by chemical composition were selected based on the results of spectral analysis of the samples (Table 1). Table 1 presents the chemical composition data of pipe certificates closest to the samples studied. All three investigated pipe samples correspond to low-alloy steel 09Mn2Si in terms of chemical composition.

Table 1. Chemical composition of the samples and pipe lots corresponding to them

Content of chemical elements,% C Si Mn Cr

Sample

Ni

P

S

Cu

Fe

No. 1, pipe Ø529 with a wall thickness of 9 mm

0.09

0.60

1.60

0.04

0.04

-

-

0.08

balance

Certificate No. 3343, Lot No. 686

0.10

0.61

1.51

0.07

0.05

0.024

0.026

0.05

balance

No. 2.1, pipe Ø529 with a wall thickness of 7 mm Certificate No. 1539, Lot No. 166 No. 2.2, pipe Ø529 with a wall thickness of 9 mm.

0.10

0.65

1.70

0.07

0.07

-

-

0.12

balance

0.09

0.72

1.68

0.07

0.05

0.030

0.040

0.12

balance

0.10

0.60

1.63

0.05

0.05

-

-

0.07

balance

Certificate 3343, Lot number 686

0.10

0.61

1.51

0.07

0.05

0.024

0.026

0.05

balance