Abstract
Many cryogenic heat exchanger applications use aluminum pressure vessels that are connected to stainless steel piping typically either by dissimilar metal flange pairs or aluminum to stainless steel transition joints. Transition joints can provide a number of advantages over flanges. Transition joints can save space and weight over flanges, and provide a leak tight connection which can eliminate fugitive emissions. Aluminum to stainless steel transition joints have been built using different technologies, including:
1. Friction welding
2. Explosion welding
3. Nonwelded, diffusion-bonded (heat shrinkage/hot pressing assembly)
This paper focuses on explosion-welded transition joints, although some of the concepts discussed may also apply to other technologies. ASME Pressure Vessel and Piping codes do not provide specific design guidelines or qualification requirements for these joints. ASME Code Case 2493 provides qualification requirements for explosion welding of dissimilar metal plates, but not for the final transition joint design. This paper shall highlight an approach to addressing specific concerns regarding the qualification and production testing of explosion-welded plates and transition joints for cryogenic applications. It shall also cover aspects of the design, qualification, and rating of the cryogenic transition joints made from explosion-welded parent plates.
ASME B31.3 Section 304.7 Pressure Design of Other Components addresses the pressure design of unlisted components in 304.7.2, which provides four acceptable qualification methods. This paper will discuss two of those methods: proof testing and detailed stress analysis, i.e., Finite Element Analysis (FEA). A combination of these two methods can be used to ensure a safe and effective design.