PSI - Issue 30

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

147

4

The results of mechanical tests for static tension and impact strength of the base metal of the pipe and welded joint are demonstrated in Table 2. In the table, the data of the certificates listed in Table 1 are given under each value of the mechanical characteristics of the samples.

Table 2. Results of mechanical tests

Average value of the mechanical characteristics

a, J/cm 2 , at -20 º С

a, J/cm 2 , at -70 º С

Sample

YS, MPa

TS, MPa

E,%

No. 1, base metal of the pipe Ø529x9 mm

405

515

34

191

114

Certificate No. 3343, Lot No. 686

360

520

34

-

59

No. 2.1, base metal of the pipe Ø529x7 mm

388

535

20

68

52

Certificate No. 1539, Lot No. 166

390

540

27,0

-

75

No. 2.2, base metal of the pipe Ø529x9 mm

358

518

28

80

41

Certificate No. 3343, Lot No. 686

360

520

34

-

59

137 – WM 119 - FL

58 – WM 66 - FL

Pipe welded joint - No. 3

412

554

23

The results of mechanical testing of the samples were compared with the data of certificates for pipes. The analysis of the results revealed the following:  sample No. 1, the yield strength of the base metal of the pipe Ø529x9 mm is 11% higher than the certificate data. An increase in the yield strength is specific for strain aging during a long-term operation, the same results shown by Mishet’yan A.R. et. al. (2018), Yoo J. Y. et. al. (2009) and Cheng Frank Y. (2013). However, dynamic tests showed conflicting data – the impact strength of the base metal of the pipe is 48% higher than the certificate data and is 114 J/cm2 on average.  sample No. 2.1, the yield strength and strength values of the base metal of the pipe Ø529x7 mm are approximately equal to the certificate data. A decrease in the following characteristics was detected: elongation by 26% ( δ 0.5 = 20%), and impact strength by 23-40% (KCU at -70°C - 52 J/cm2) compared with the certified data. The decrease in mechanical properties is possibly associated with the degradation processes. In general, the discovered mechanical properties satisfy the requirements of regulatory documents for 09Mn2Si steel.  sample No. 2.2, the yield strength and strength of the base metal of the pipe Ø529x9 mm are approximately equal to the data of the certificates. The following characteristics were decreased: elongation by 18% ( δ 0.5 = 28%), and impact strength by 30-34% (KCU at -70°C - 41 J/cm2) compared with the certified data. An analogy is observed with the data of sample No. 2.1 related to the occurrence of degradation processes. In general, the discovered mechanical properties satisfy the requirements of regulatory documents for steel of 09Mn2Si grade.  a sample of the welded joint of pipe No. 3, the values of temporary resistance, as well as the impact strength of the base weld metal and the heat-affected zone are higher than the values of the base pipe metals (samples No. 2.1 and No. 2.2). During a static tensile test, a fracture of the samples occurred on the base metal. 4. Conclusion According to the research results, it has been established that significant changes in the mechanical properties of the base metal of the pipe after a long-term operation were not detected in the first sample. In the second sample, the relative elongation decreased by 18 ... 26% and the impact strength by 23 ... 40%, as compared with the certificate