During a new plant startup a high pressure heat exchanger was subjected to significant thermal gradients and experienced a leak. The joint was modified and a new type of gasket was selected to eliminate the leakage. Several studs were instrumented with strain gages to gain a better understanding of the loading experienced during torquing and due to the gradients occurring during startup and normal operation. In addition to the strain gages, the temperature gradients in the flange were measured using 26 thermocouples. This paper presents the data obtained from the instrumented studs and thermocouples over a span of five months and summarizes the lessons learned. These included an assessment of the error in various bolting techniques, the benefit of bolting techniques such as multiple jack bolt tensioners, and the nature and effect of thermal gradients in flanges, the effects of spring washers on the magnitude of thermally induced loads, and problems arising from gasket quality control. Recommendations to improve the leak tightness of large diameter heat exchanger joints experiencing thermal gradients are presented.

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