Abstract
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.