Powder Plasma Arc Butt Welding of Boiler Pipes

Abstract

Powder plasma arc welding is a favourable method for the industrial welding, but it still lacks of successful experiences. However it has obviously a higher productivity and it produces good welding quality.

When the method is applied for pipe welding, the difficulties to achieve the proper closing of the keyhole has prevented practical application of it for a long time. In this study, the porosity at the closing position of the keyhole position has been studied seriously and finally eliminated by a set of optimised welding parameters. For closing the keyhole without porosity, it is necessary to apply a suitable slope to reduce the welding current and plasma gas flow rate, and to apply 20° overlapping to achieve proper connection between starting and ending as well as to reduce the welding current 10 % to overcome the preheating from starting position.

Metal powder as a filler material is suitable for I-groove, single pass welding. It needs no complex equipment for tracking the weld center line, that means easier operation and simple welding equipment. Powder filler is especially suitable for manual welding.

A set of welding parameters has been outlined that give good weld joint quality for the circumferential welding. According to this study, it can be concluded that for powder plasma welding process of pipes, high reliability is crucial for repeatability and quality of welding. The powder plasma welding process has a narrow range of working parameters.