PSI - Issue 22

Li Yan-hua et al. / Procedia Structural Integrity 22 (2019) 118–124 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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aging at -10 ℃ . While the impact energy would increase slightly with the increase of aging temperature and aging time. 4. Tensile properties The test result of tensile properties of X90 line pipes in transversal direction under different aging conditions are shown in Table 3 ～ Table 5.

Table 3. The test result of tensile mechanical properties of sample A in transversal direction under different aging conditions

Aging at 200 ℃ for 5 Mins

Aging conditions Without aging

Aging at 250 ℃ for 1h

R p0.2 /MPa

693 790

742 780

736 770

R m /MPa

R p0.2 /R m /%

88

95

95

Table 4. The test result of tensile mechanical properties of sample B in transversal direction under different aging conditions Aging conditions Without aging Aging at 200 ℃ for 5 Mins Aging at 250 ℃ for 1h R p0.2 /MPa 636 699 698 R m /MPa 746 740 740 R p0.2 /R m /% 85 94 94 Table 5. The test result of tensile mechanical properties of sample C in transversal direction under different aging conditions Aging conditions Without aging Aging at 200 ℃ for 5 Mins Aging at 250 ℃ for 1h R p0.2 /MPa 704 792 802 R m /MPa 791 811 824 R p0.2 /R m /% 89 98 97 It can be obtained from Table 3 ～ Table 5 that the tensile strength would decrease for specimen A and B, while the tensile strength would increase for specimen C. The yield strength and yield ratio would increase significantly after aging, and the rising range of yield strength and yield ratio would decrease with the increase of aging temperature and aging time. 5. The aging sensitivity of X90 line pipes Strain aging sensitive coefficient is introduced to characterize the strain aging sensitivity of steel. A certain amount of plastic deformation would occur on the X90 line pipe during the forming process, and the coating temperature would reach to 200 ℃ ~250 ℃ during the anticorrosion process, as a result, the production process of pipes has significant effect on the tensile properties of pipeline steel. There is close connection between the strain aging sensitivity and tensile properties of pipeline steel. The yield strength and yield ratio would increase after strain aging. As a result, the increase percentage of yield strength and yield ratio after the introduction of aging can be adopted to denote the strain aging sensitive coefficient of steel. Study on the early results of X80 artificial strain aging shows that the yield strength and yield ratio of X80 pipeline steel increased significantly. The results of X90 artificial strain aging shows that the performance of this law is still evident, but the change magnitude of tensile strength is small. Adoption the thought of GB 4160, the ratio of mechanical properties of pipeline before and after strain aging is introduced to quantify the aging sensitivity of X90 pipeline steel.