Submerged arc - SIAD Società Italiana Acetilene e Derivati
Submerged arc header
Submerged arc welding is an autogenous welding process by melting whereby thermal energy is supplied by the arc shooting out between a fusible, continuously fed, wire electrode and the weld piece.
Protection of the arc is provided by a layer of granular and meltable flux distributed along and above the joint in front of the arc, which covers the weld pool and the base metal near to the joint; the arc therefore shoots out below the flux layer and is thus invisible (hence the origin of the name “Submerged Arc”).
Thermal energy provided by the arc provokes the melting of the wire, base material and part of the flux. Base materials and filler materials become mixed in the melted state and then solidify to form the weld bead. The part of the flux which is melted undergoes a chemical reaction with the bath and, therefore, creates slag which has to be removed later. The need for a layer of flux to be distributed along the joint and the considerable volume of the weld pool does not permit welding to be carried out in position. For this reason, submerged arc welding can be carried out only on the flat and on a level plane.
In submerged arc welding both continuous or alternating current can be used. The tendency is, however, to use continuous current which gives greater consistency in penetration and a more regular development of the metallurgical phenomenon in the bath.
Submerged arc welding can be used either automatically or semi-automatically.
The procedure is used, with good results, in the welding of mild steels, high resilience medium carbon steel, low alloy steel and, with the necessary precautions taken, even for stainless steels. Other materials are weldable using particular precautions to limit the number of passes, especially when a high level of toughness is required at low temperature or where they are, in fact, not weldable.
In principle, with regard to head joints in carbon steel or low alloys, submerged arc welding is used without any problems on thicknesses above 8mm and without any upper thickness limit.
The procedure is used in the following sectors: