Investigation of a Chronic Leaking Problem of a Heat Exchanger Girth Flange

A shell-and-tube heat exchanger experiences frequent leaks from the gasket between the shell girth flange and tube sheet. The leaks manifest during start-up of the equipment and have traditionally been arrested by assembly retorque. An investigation was launched to understand the cause of recurring leaks and propose measures to eliminate the problem. A standard design review using the ASME BPVC [1] rules for bolted flanges found no concern with the design of the flanges. More detailed numerical simulation studies were performed that considered thermal conditions in addition to mechanical loads (pressure and bolt loads). The heat exchanger operation involves phase changes in the media on both the shell and tube sides (boiling/condensing) — as a result, the flanges experience rather severe thermal gradients during regular operation. These thermal gradients cause distortion of the tube sheet and girth flange and result in relaxation of the gasket compression in specific areas. This paper will provide a detailed discussion about the numerical simulation studies that were performed on the girth flange joint, as well as the modifications that were proposed to alleviate the problem.