TENSILE STRAIN CAPACITY MODEL OF X65 STEEL PIPE UNDER PRE-STRAIN EFFECT AND CRACK-TIP CONSTRAINT

• Main Author: Ikhsan, Ilmi
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/55156
• Institution: Institut Teknologi Bandung

Response to geohazards or mechanical loading during pipeline installation or services naturally occurs and cause displacement in length, deform plastically and potentially lead to failure. Various contributed parameters to strain-based solution become more complex with pre-strain history. Until now, strain-based guidelines are still limited, especially for large pre-strain beyond yield which is followed by crack or crack-like-flaw defect. The cases with such large pre-strained near to collapse condition so that stable crack growth assessment can be ignored because the yield occurred is near to the ultimate. In this research, plasticity response was tested first to evaluate the stress-strain behavior in plastic zone between yield and ultimate strength and remaining strain capacity under several pre-strain level and cracked area parameter. Here, X65 pipe steel specimens are subjected to crack after pre-strain and fracture response was quantified by relation of crack-tip opening distance with Qp-constraint parameter by utilizing finite element analysis to generate the crack-tip stress field. The maximum strain was measured on its ultimate strength point for several level of pre-strain with sequence of: loading-unloading, introducing of blunted crack and reloading. As the result, remaining strain capacity was reaching ?r = 0.4% when pre-strain level was ?o = 5.2% and. It is also known that stress-strain curve in platic zone between the yield to ultimate strength is near to linier due to pre-strain. ?-Qp parameter is proposed here as part of fitness-for-service assessment procedure for defected steel pipe occurred after pre-strained. For geometrical and defect studied in this research, „failure? condition was presented in value combination of ? > 0,03 mm and Qp ~ -0.5