Patent ID: 7253372

Claim:
A method for welding comprising the steps of: a) obtaining a heat-exchanger tube having first and second tube ends, having a tube wall, having a tube centerline, and having a first outward fold disposed toward the first tube end, wherein the first outward fold includes a first portion of the tube wall which extends outward from the tube centerline and then turns and extends back inward toward the tube centerline as one travels along the tube toward the first tube end; b) obtaining a heat-exchanger first tubesheet having an outward-facing side and an opposing inward-facing side and having an orifice; c) inserting the tube at least partially through the orifice of the first tubesheet with the first outward fold contacting one of the outward-facing side and the inward-facing side of the first tubesheet; d) disposing a first electrode in physical contact with the first outward fold; e) disposing a second electrode in physical contact with the one of the outward-facing side and the inward-facing side of the first tubesheet; and f) using the disposed first and second electrodes to resistance weld the first outward fold of the tube to the first tubesheet.