Lack of Fusion on Socket Weld Joints – A Case Study

Introduction

Inspecting welds during piping construction is a basic element of a robust QA/QC program. The minimum requirements for inspecting process piping in the petroleum and chemical processing industries are established in ASME B31.3 and other complementary codes and practices. When weld defects or discontinuities are discovered during inspection, it is critical that they are not ignored, misinterpreted, or handled the wrong way.

Socket welds are typically simpler and easier to perform than butt welds. For this reason, the importance or priority of inspection requirements for socket welds may not be taken as seriously following construction. However, complications due to low diameter, geometry, procedure, and qualification of welders have resulted in flaws being overlooked, introducing an increased potential for loss of primary containment and safety incidents.

Therefore, improving the process to clarify welding procedures, verify welder qualifications, and capture important data can improve the integrity of socket welds and help mitigate mechanical integrity risks.

Context

During a refinery turnaround, the fabrication and installation of 316 stainless steel piping was performed. After QA approval, the QC program review was in progress when an unusual issue was discovered. A trend indicating an issue with lack of fusion on socket welds was becoming increasingly evident, and after more data was gathered, it became clear that it was a widespread problem. The QC program required performing radiographic testing (RT) of over 30% of the total socket weld joint to verify that the gap requested for this type of joint per ASME 31 was achieved. After performing the first 98 RTs, 20 welds showed evidence of a common flaw -- lack of fusion in the roots.