Structural Welding of Thick-Walled Pipes by Keyhole Plasma Arc Welding and Powder Finishing

摘要

The use of Plasma Arc Welding technique (PAW process) together with a tailored equipment facing the process new demands proves that structural welds on thick-wall pipes is possible, by joining two or more sections of centrispun tube materials. Plasma Arc Welding technique, in keyhole mode, assures a deep and complete root penetration in the first pass (at root surface) with high quality from both the production requirements and the control of structural characteristics of the joint. The groove finishing by Powder Plasma Arc Welding (PPAW), performed in single pass after the first in keyhole mode, represents the most innovative and attractive aspect of this technique, gaining a perfect near-to-net shape at face of weld, thus leaving the two joint beads (face and root of weld ) in the as-welded state. The paper briefly describes the PAW technique in keyhole mode and the melt-in variant with powders as filler material, the main characteristics of the welding equipment, the control and optimisation of the operative variables which mostly influence the welded joint shape.