A. Finning

(a) Welded fins

The fins are formed from strip into a U channel and welded onto the inner pipe using an electric resistance scam-welding technique. The U channels, two at a time, are clamped onto the pipe by circular electrodes under hydraulic pressure. A very high current is passed through the electrodes, which are also driven, thus moving the pipe through the machine. The weld takes the form of a series of spots such that complete fusion takes place between the fin root and pipe.

This technique is suitable for carbon steel, stainless steel, monel, and even titanium under controlled conditions.

Combinations of materials can also be utilized, such as a stainless steel inner pipe with carbon steel fins. This is a very useful combination, as it increases the fin efficiency by using carbon steel fin while still retaining the corrosion resistance of the inner pipe.