Welded Longitudinal Finned Tubes are produced by resistance welding fins in the longitudinal direction along the length of the tube. The fin strip is first formed into a U-shaped channel, such that each leg of the U will form a fin. The channels are cut to the appropriate length and then oriented along the length of the tube and resistance welded in place. The channels are welded in pairs, diametrically opposed — therefore the number of fins specified must always be a multiple of four.

For a given pipe or tube size, the desired heat transfer surface area per unit length of tube can be obtained by specifying the appropriate fin height and number of fins. The maximum number of fins is dependent upon the tube outside diameter — larger OD tube can accommodate a greater number of fins. See Design Information for extensive tables of surface areas and fin weights.

Some customers specify that the longitudinal finned tubes be “Cut and Twisted.” This operation consists of cutting through the fin channels circumferentially at specified intervals along the tube length. The fins are then bent (or “twisted”) on one side of each cut, creating a discontinuity that promotes turbulent fluid flow, thereby enhancing heat transfer efficiency.