Mechanical performance and deformability of X80 steel girth welded joints with different strength matching

Abstract

The strength matching and toughness of girth welded joints are very important to the service safety of pipelines. In order to better understand the failure mechanism of girth weld, the microstructure and properties of two types of high-Nb X80 girth welded joints with different strength matching were tested by mechanical performance testing and microstructure analysis. Meanwhile, the strain behavior of the welded joints applied with the tensile load was studied by the digital image correlation (DIC) method. The results show that both of the undermatched and overmatched girth welded joints have good impact toughness and similar average Charpy impact absorption energy. Under the tensile load, strain concentration appears in the root welds and the heat affected zones (HAZ) at first. With the increase of tensile load, the strain concentration of the overmatched girth welded joint shifts to the base metal gradually, and the bearing capacity of the pipeline to the axial load and deformation is greater than that of the undermatched girth welded joint. Additionally, the undermatched girth welded joints are prone to fracture due to the plastic strain accumulation in the weld and HAZ, even if they have good toughness.

Keywords

• high-nb x80 steel
• strength matching
• girth weld
• strain accumulation
• digital image correlation method