Submerged Arc Welding

Submerged arc welding is a common welding process that is often used in industries such as structural and vessel construction.  Also known as Sub-Arc or SAW, this process uses a blanket of granular fusible flux, beneath which both the weld and the arc zone are protected or &#;submerged.&#;  This flux blanket guards against atmospheric contamination, stabilizes the arc during welding, prevents splatter and sparks from flying about, and suppresses radiation and fumes that are typical of the shielded metal arc welding process.

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Throughout the submerged arc welding process, the flux has to be a continuously-fed tubular or consumable solid electrode.  This fusible flux may consist of lime, silica, manganese oxide, calcium fluoride, and other compounds.  In a molten or melted state, the flux becomes conductive.  This allows it to supply a constant current between the electrode and the welding work.

The SAW process is usually automated; however, there are semi-automated systems available, too.

Material applications of SAW include carbon steels, low alloy steels, stainless steels, nickel-based alloys, and surfacing applications (wear-facing, buildup, and corrosion-resistant overlay of steels).  SAW is frequently used in heavy structural construction.  It is also used in the pressure vessel industry, chemical plants, and shipbuilding.

Properly performed Sub-Arc welding should consistently result in mechanical properties that are at least equal to that of the base metal.  Ductility and impact resistance should be good, and bead appearance should be uniform.

Advantages of Submerged Arc Welding

Some of the advantages of submerged arc welding include:

• Strong, sound welds are readily made
• Minimal welding fume is emitted
• Minimal arc light is emitted
• SAW is suitable for both indoor and outdoor works
• Less distortion
• Deep weld penetration
• Minimal edge preparation
• High deposition rates are possible
• Thick materials may be welded
• At least half or more of the flux is recoverable

Disadvantages of Submerged Arc Welding

There are a few limitations with submerged arc welding.  One issue is that welding can normally be performed only in the flat position.  The use of a granular flux and the fluidity of the molten weld pool mean that welding is limited to positions 1F, 1G, and 2F.

Another disadvantage of SAW is that welding is normally limited to long, straight seams or rotated vessels or pipes.  Flux handling systems can be quite bothersome, as well.

Also See

Variations of Submerged Arc Welding

The Submerged Arc Welding (SAW) Process

Submerged Arc Welding (SAW) is a joining process that involves the formation of an electric arc between a continuously fed electrode and the workpiece to be welded. A blanket of powdered flux surrounds and covers the arc and, when molten, provides electrical conduction between the metal to be joined and the electrode. It also generates a protective gas shield and a slag, all of which protects the weld zone.

The make-up of the process can be viewed by reference to Figure 1 below

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Figure 1. The Submerged Arc Welding Process

As can be seen from Figure 1, the arc is "submerged" beneath a blanket of flux and is, therefore, not usually visible during the welding operation itself. These facts make the process advantageous from a health and safety viewpoint as there is no arc to promote "arc eye" and very little fume.

There are two welding consumables involved in the process, the electrode and the flux. The electrode can be a solid wire, a cored wire, or a strip. The flux, made from a variety of minerals and compounds, can be rather complex and can be produced in a number of forms.

The general arrangement of the power source and controls, wire feed and flux dispensing are shown in Figure 2.

Figure 2. General Arrangement of the Submerged Arc Process

Submerged arc welding is viewed as a high productivity process and is usually automated/mechanized in its form. The simplest application of the process uses a single wire.

Selecting the correct wire diameter for a welded joint depends on many factors and the size of the available power source usually limits the diameter of the wire that can be used. While most power sources for this process are 1,000 amps, smaller power source may be used. A 3/32-in.-dia. wire through to a 5/32-in.-dia. wire will run in the 300 to 900 amps range using direct current and with the electrode positive (DC+)

This welding process is typically suited to the longitudinal and circumferential butt welds required in the manufacture of pressure vessels and for joining plating and stiffeners in shipyards. Welding is positionally restricted and is normally carried out in the flat or horizontal positions because of the highly fluid weld pool, the molten slag, and the need to maintain a flux covering over the arc.

As with all welding processes the selection of the consumables (wire and flux) and other parameters such as amps, volts and travel speed are intended to give a weld deposit that satisfies the objectives of the designer. In the case of this welding process, since the arc is submerged, the welding operator cannot see the molten weld pool and must, therefore, very accurately set the welding parameters and location of the welding nozzle within the joint.

Submerged arc welding has many advantages but there are also restrictions, some of these are listed below

Advantages

• High deposition rates and high arc on times when fully automated.
• Minimal welding fume, no weld spatter and no visible arc
• Unused flux can be recovered
• If metallurgically acceptable, single pass welds can be made in relatively thick plates.

Restrictions

• Limited to steels, although some consumables have been developed for other materials such as nickel-based alloys.
• Cannot be used in the vertical or overhead welding positions. Used principally for butt welds in the flat position (1G) and fillet welds in the flat and horizontal position (1F & 2F). Horizontal butt welds can be made but special devices are required to support the flux.
• Requires separate flux handling systems and slag removal between passes.
• Not realistically applicable to thin materials.

There are many more applications of this welding process, other than its use with a single wire, and the fluxes used can be quite complex in their design and production. These items may be covered in later articles.

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