Integrity of Roller Expanded Tube-to-Tubesheet Joints With Over-Enlarged Tubesheet Holes

This paper presents the results of an experimental investigation conducted to evaluate the effect of initial tube-tubesheet diametral clearance on the integrity of roller expanded tube-to-tubesheet joints in over enlarged tubesheet holes. The criteria of evaluating joint integrity include the pull out force and hydraulic tightness of the joints in which tubes were expanded to 5% wall reduction after metal to metal contact of the tube with the tubesheet hole. The levels of clearance investigated were selected to cover a range that exceeded by ten times that prescribed by the Tubular Exchangers Manufacturers Association (TEMA) standards [1]. The pull out test results showed that, within the investigated range of clearance, the joint strength has not declined below the strength of joints with clearance levels within the TEMA range. In fact the pull out force exhibited a slight linear increasing trend with the increase in initial clearance, which is attributed to the effect of tube strain hardening. The hydro test results indicated that all joints within the investigated clearance levels were hydraulically tight when they were tested at 1.5 times the design pressure of the heat exchanger for duration of 30 minutes. A relationship between rolling specific energy and initial joint clearance has been developed.