Integrity of roller-expanded tube-to-tubesheet joints with overenlarged 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 overenlarged tubesheet holes. The criteria of evaluating joint integrity include the pullout 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 (Standards for the Tubular Exchanger Manufacturers Association, 1988, 7th ed., TEMA, Tarrytown, NY). The pullout 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 pullout force exhibited a slight linear increasing trend with the increase in initial clearance, which is attributed to the effect of tube strain hardening. The hydrotest 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 a duration of 30 min. A relationship between rolling specific energy and initial joint clearance has been developed.