Internal pneumatic clamps are used to hold the two pipes in position during the first welding pass. It is supplied with the copper internal back-shoe system. It sets the gap between the joints evenly all the way around the pipe. It is available in many diameter ranges. For field welding two pipes, an automatic spread bevelling machine and standard internal pneumatic clamp are necessary.
The simplest form of reboiler is the internal boiler, which consists of a bundle of tubes, usually U-tubes, containing the heating fluid, which is inserted into the pool of liquid at the bottom of the distillation column. This type of boiler is very cheap but suffers from two disadvantages like the distillation column is rarely wide enough to allow a bundle of sufficient surface area to be accommodated and it is difficult to support the end of the bundle, but this can usually be accomplished.