EFFECT OF ARTIFICIAL CRACK ASPECT RATIO ON TENSILE AND COMPRESSIVE PROPERTIES OF WELDED API X70 STEEL

Abstract

Pipelines are joined by welding and are used for transportation of oil and gas products globally. These joints are prone to surface defects and sometimes deep cracks depending on types of loading they experience while in operation. Hence, it is necessary to understand the effect of defects on mechanical properties of welded pipeline joints to estimate their service lives. In this study, both experimental and numerical approaches were used to study the effects of aspect ratio on pipeline integrity. Artificial cracks were created on API X70 steel tensile and compression specimens using different aspect ratios. Universal Testing machine was employed in carrying out the experimental and ANSYS 2019 2R was used for modelling and loading of the specimens. Results show that the investigated mechanical properties were not only sensitive to materials type (weld and base) but also to aspect ratio. The tensile maximum stresses for experimental and numerical result for plain and weld materials without artificial crack aspect ratio was determined to be 706.8 MPa and 1176.9 MPa for plain materials, while 667.8 MPa and 646.92 MPa for weld materials respectively. The compression strength was 1200.4MPa and 1300.2 MPa for plain, while for weld 1393.7 MPa and 1902.1 MPa respectively. For specimens with artificial crack aspect ratios, tensile results are 706.8 MPa and 1776.9 MPa for Plain at aspect ratio of 0.2 respectively, while weld are 667.8 MPa and 646.93 MPa at aspect ratios of 1.0 and 0.2 respectively. That of compression were 1238.5 MPa and 1637.9 MPa at aspect ratios of 1.0 and 0.2 for plain, 1500.5 MPa and 1929.9 MPa at aspect ratios of 1.0 and 0.2 respectively. The maximum stresses obtained for tensile and compression specimens with or without artificial crack aspect ratios were discussed.