INVESTIGATION OF THE EFFECT OF TEMPERATURE ON FRACTURE BEHAVIOUR OF WELDED API X70 STEEL

Abstract

Oil and gas production has significantly increased over the years in order to meet present demands for oil and gas products, regardless of the unstable price being experienced by producing Nations. The use of pipelines for the transportation of these products has been the globally recognized solution. These pipelines are fabricated by welding and their fracture properties depend on a number of factors which include temperature, particularly for the pipelines operating in cold region such as deeper water depths. Therefore, information of fracture behavior of welded pipelines located in cold regions is therefore important for reliable design service. In this work, the effect of temperature on fracture behavior of welded API X70 steel was investigated using Charpy V- notch specimens. The scanning electron microscope (SEM) and spectroscosopic analyses were carried out on the fractured surfaces of parent and weld specimens. Impact tests were carried out on weld and parents at temperatures -100C, -200C, -400C, -600C, - 800C, -1000C, -1200C, -1600C, 00C, 100C and 200C. Results reveal that higher energy was absorbed in the weld than in parent materials regardless of the test temperature used. The Charpy energy dropped from 145.6 J to 12.3 J as the test temperature were reduced from 200C to -1600Cwhich implies that energy absorbed during charpy test is sensitive to temperature. The tensile properties of parent and weld materials were determined at room temperature. The mean yield and strength as well as the mean yield /tensile ratio of the parent materials were determined to be 561.05Mpa, 632.50Mpa and 0.89 respectively. Meanwhile, the mean yield and strength and the mean yield/tensile ratio of the weld materials were determined to be 575.69Mpa, 668.61Mpa and 0.86 respectively.