Study of Tensile Deformation and Damage Law in Undermatching X80 Pipeline Steel Welded Joints

Abstract

This study used a digital imaging technique (DIC) to obtain the strain distribution at various locations in undermatching X80 pipe girth-weld joints under uniaxial tensile loading. In addition, the microstructure characteristics and deformation patterns in different regions were analyzed by scanning electron microscopy (SEM). The results showed that there was strain heterogeneity between the various regions of the welded joint. Strain concentration existed only in the 12.8 mm base metal heat-affected zone (HAZ) and only in the elastic deformation stage. There was strain concentration in the weld metal (WM) and both sides of the HAZ close to the near-fracture stage, and the maximum deformation was in the WM. When εM = 12.2%, the KC was 6.27 and the KF was 1.73, and the KF was 113% and 152% of the KC and the KG, respectively. The large number of slip strips generated indicated serious damage in the WM near the fracture stage. In the elastic deformation stage, the strain concentration of the N1 HAZ was caused by the softened ferrite. The maximum deformation of the WM near the fracture stage was caused by the large grain size and the non-uniform martensite–austenite (M–A) islands, which may also lead to better local toughness of the cover weld and further affect the fracture mechanism of the welded joint.

Effect of pre-strain on microstructure evolution and fracture behavior of undermatching X80 pipeline steel girth weld

“…The results show that the carrying capacity of the girth weld is greatly reduced due to shearing action. Previous studies [17] clarified the strain law, deformation behavior and microstructure characteristics of undermatched X80 welded joints in practical applications. The pattern of strain concentration in the weld region varies in different tensile stages, leading to severe damage and final fracture of the weld.…”

Crack Size and Undermatching Effects on Fracture Behavior of a Welded Joint

“…It was shown that even in the case of a ductile structural steel (S235), fracture can occur at a relatively low stress level. Another study with DIC was performed to obtain the strain distribution in undermatching X80 pipe weld joints under uniaxial tensile loading, [ 18 ]. The results showed that the maximum strain was in the WM.…”

The Simulation of Extremely Low Cycle Fatigue Fracture Behavior for Pipeline Steel (X70) Based on Continuum Damage Model

“…Pipeline steel is generally required to have high plasticity and toughness. Under large strain loads, pipeline steel undergoes ductile fracture, accompanied by the nucleation, growth and coalescence of void at the microscopic level [8,9,12]. At low temperatures, brittle fracture of the pipeline steel may occur due to a decrease in toughness [10,13].…”