Session: 03-02-01: Integrity and Performance of Welded Joints

Submission Number: 156124

Microstructure and Effect of Orientation on Toughness of X65 Steel Pipe Electric Resistance Seam Weld 

This study investigates the microstructure and toughness of a commercial electric resistance welded (ERW) X65 pipe by characterizing both the base metal (BM) and the bond line (BL) or fusion line. The analysis aimed to correlate these microstructural features with the pipe’s mechanical toughness. To evaluate how crack orientation affects toughness, Charpy and square-sectioned B×B single-edge-notched bend (SEB) specimens were tested in both the Charpy lower-shelf (brittle cleavage) and upper-shelf (ductile) regions. The findings revealed that the ERW weld lacked evidence of proper post-weld heat treatment (PWHT) or may not have undergone any PWHT, contributing to poor toughness. The microstructure displayed inhomogeneous microstructure, large irregular ferrite grains, a high density of preferential cleavage planes parallel to the fracture plane, and the presence of hard phases and inclusions. These factors likely accounted for the material's low toughness. Fractographic analysis indicated that cleavage fracture initiated at inclusions and hard phases present at the BL. In one case a flaw contributed significantly to fracture initiation. The study also showed that crack orientation had minimal influence on Charpy absorbed energy (CVN) and fracture toughness (J-integral). Toughness in through-thickness-notched (TTN) specimens was either comparable to or slightly lower than in surface-notched (SN) specimens.  This supports the use of TTN Charpy specimens for conservative qualification of welds.

Presenting Author: Tirdad Niknejad CanmetMATERIALS (CMAT) / Natural Resources Canada / Government of Canada

Presenting Author Biography: Tirdad Niknejad is a dedicated research scientist specializing in welding metallurgy, failure analysis, and modeling the mechanical behavior of metals. Holding a PhD in Mechanical Engineering from the University of Waterloo, he has made significant contributions to both scientific research and industrial applications.

Tirdad's primary focus is the assessment of structural integrity in pipeline infrastructures for alternative energy transport, with a particular emphasis on weld evaluation for hydrogen and CO₂ pipelines. His experience spans a wide range of projects, from fusion welding of various metals to stress-strain analysis and research into advanced high-strength steels and aluminum alloys. Tirdad's work bridges the gap between fundamental research and practical industry solutions, fostering interdisciplinary collaboration across multiple fields.