TWI Frequently asked questions
Stove pipe welding is one of the chief methods used in the field welding of pipelines for oil, gas, water etc. It is a variant of the manual/shielded metal arc welding (MMA/SMAW) technique used for positional welding, enabling steelpipelines to be laid at high production rates. The vertical-down technique is predominantly used, consisting of multiple runs in the 12 to 6 o'clock position.
Cellulosic or cellulosic-iron powder coated electrodes are used (ISO 2560-A (B) - E XX X XXX C or AWS A5.1-2004 EXX10 or EXX11). These contain organic compounds containing relatively high levels of hydrogen which give a highburn-off rate, forceful arc and a light, fast-freezing slag - all very suitable for the vertical-downward technique. The coating also provides a gas shield which is less affected by wind than other electrodes (though weather protectionmay still required).
The weld preparation typically consists of a 60-70° bevel (inclusive angle), with a 1-2mm root face and 2-3mm root gap. Stringer beads are deposited into the root at high speeds (250-300mm/min). This is immediately followed bya hot pass which refines the root pass and reduces the risk of hydrogen cracking associated with these consumables. A minimum level of preheat is often required for the same reason. Filler runs, stripper runs and capping run(s)complete the welding. The welding of pipelines is usually performed by a team of welders; the larger the diameter of pipe, the greater the number of welders. In most cases each welder performs the same weld run(s) on each successivejoint.
BS EN ISO 2560:2005 Welding consumables. Covered electrodes for manual metal arc welding of non alloy and fine grain steels. Classification ANSI/AWS A5.1-2004 Specification for carbon steel electrodes for shielded metal arc welding.
