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Maintaining the minimum allowable distance between proximity welds has always been considered a subject of debate among design engineers, welding engineers/inspectors and fabricators/engineering contractors. The scattered nature of guidelines available in welding codes and standards for maintaining the minimum allowable distance poses a significant challenge in the welding procedure and inspection criteria development process. This is especially critical for complex welded joints on submerged sections of offshore structures, in compact layouts/branched connections of topside piping components, and on topside structural joints (depending on the complexity). This manuscript presents the findings of an experimental study that was performed by fabricating two girth welds at proximity on an S355 steel tubular section with diameter of 219.1 mm and thickness of 8.18 mm. Proximity girth welds were fabricated on S355 tubular sections at three different distances between their weld toes, 5, 10, and 15 mm, respectively, using two different welding procedures. Welding procedure qualification record (WPQR) was performed, and all prescribed mechanical tests were recorded as per NORSOK M-101, a structural steel fabrication code. Although all results from the mechanical test met the minimum specified values as defined in the NORSOK code, the research findings revealed a noticeable difference in Charpy and hardness values for proximity region between adjacent welds. Considerable changes in final microstructure morphology were observed between proximity welds due to varying thermal cycles. These observations can form the basis for the future welding procedure qualification of critical welded joints, especially for proximity welds on critical welded joints of offshore structures and welds fabricated during replacement/repair procedures in compact piping layouts.

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In offshore structures, pipelines and piping, there are various configurations where welds are often in close proximity to each other. TKY joints in offshore structures, welds of nozzles, tees, elbows and circumferential welds of piping in compact layouts are a few examples. Depending on their application, different codes (ASME B31.3, ISO 19902, etc.) either recommend different criteria or provide no explanation for deciding a minimum distance between proximity welds. The guidance provided in these codes is inadequate for a field inspector to make an informed decision on site. Some international standards specify a minimum distance between welds, based upon some factor regarding the diameter or thickness of the parts under welding or they give no explanation, which creates an ambiguity among contractors and inspectors on site. The overlapping of two adjacent heat affected zones (HAZ) can have a deleterious effect on the material properties of the metals, eventually leading to catastrophic failures in the life cycle of high-risk components like offshore structures, process piping, etc. The different thermal cycles of adjacent welds with varying cooling times can drastically change the microstructure/mechanical properties of the metals, where locked in residual stress can amplify the effect towards failure. Since the aforementioned codes are deficient in providing technical justification regarding noncompliance of maintaining proximity distances, an approach for understanding close proximity effects on structural integrity is needed. This manuscript presents a brief assessment of international standards for specifying the minimum distance between close proximity welds for structural and pressure vessels’ codes. Challenges like residual stresses’ impact on fatigue strength, fatigue crack growth and fitness for service for fracture assessment are discussed briefly for proximity welds. Finally, building on the literature review, a framework for future research is presented.