What is Submerged Arc Welding (SAW)?
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.
The first SAW patent was taken out in 1935. The process requires a continuously fed consumable solid or tubular (metal-cored) electrode. The molten weld and the arc zone are protected from atmospheric contamination by being “submerged” under a blanket of granular fusible flux consisting of lime, silica, manganese oxide, calcium fluoride, and other compounds.
When molten, the flux becomes conductive and provides a current path between the electrode and the work. This thick layer of flux completely covers the molten metal thus preventing spatter and sparks as well as suppressing the intense ultraviolet radiation and fumes that are a part of the shielded metal arc welding (SMAW) process.
How Does Submerged Arc Welding Work?
Submerged-arc welding (SAW) is a common arc welding process that involves the formation of an arc between a continuously fed electrode and the workpiece. A blanket of powdered flux generates a protective gas shield and a slag (and may also be used to add alloying elements to the weld pool) which protects the weld zone.
Shielding gas is not required. The arc is submerged beneath the flux blanket and is not normally visible during welding. This is a well-established and extremely versatile method of welding.
The electrode may be a solid or cored wire or a strip made from a sheet of sintered material. The flux may be made by either fusing constituents to form a glassy slag (which is then crushed to form a powder) or by agglomerating the constituents using a binder and a corning process. The chemical nature and size distribution of the flux assist arc stability and determine the mechanical properties of the weld metal and the shape of the bead.
SAW is usually operated as a mechanized process. Welding current (typically between 300 and 1000 amperes), arc voltage, and travel speed all affect bead shape, depth of penetration, and chemical composition of the deposited weld metal. Since the operator cannot observe the weld pool, great reliance must be placed on the parameter setting and positioning of the filler wire.
Although SAW is normally operated with a single wire using either AC or DC current, there are a number of variants including the use of two or more wires, adding chopped wire to the joint prior to welding, and the use of metal powder additions.
Additional productivity may be gained by feeding a small diameter non-conducting wire into the leading edge of the weld pool. This can increase deposition rates by up to 20%. These variants are used in specific situations to improve productivity through increasing deposition rates and/or travel speed. Replacing the wire with a 0.5mm thick strip, typically 60mm wide, enables the process to be used for surfacing components.
Submerged Arc Welding Applications
The applications of Submerged Arc Welding include the following
- Submerged Arc Welding can be used to weld pressure vessels like boilers.
- A lot of structural outlines, pipes, earth-moving tools, shipbuilding, railroad construction, and locomotives.
- This type of welding can be used to repair machine parts.
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
Despite the good benefits of submerged arc welding offers. Some limitations also occur. The following are the disadvantages of submerged arc welding.
- It is limited to some ferrous metals like steel and stainless steel
- It is also limited to long straight seams or rotated pipes and vessel
- Backing strips are required for proper penetration
- It is limited to high-thickness materials.
FAQs
What is the submerged arc welding 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.
Why is submerged arc welding better?
It offers an extremely high metal deposition rate while providing high weld accuracy, fusion quality, depth of penetration, and a low rate of weld discontinuities. Other highly efficient arc welding processes, like MIG and Flux-cored, can’t match the deposition rate of the submerged arc welders.
What are the disadvantages of submerged arc welding?
The main disadvantage of submerged arc welding is that it can be used only in the flat or horizontal welding positions (test positions 1G or 2G) for plate and pipe welding.
What are the fumes from submerged arc welding?
For carbon steel electrodes, the main constituents of the fume will be iron, manganese, sodium, potassium and calcium oxides, fluorides and silicates, mainly in the form of complex oxides and other compounds. There will also be smaller amounts of other complex metal oxides and silicates.
Can you do submerged arc welding under water?
Most wet underwater welding is carried out using manual metal arc electrodes, which have a waterproof coating over the flux coating. Semi-automatic welding equipment has been developed which uses a solid wire surrounded by a gas shield, retained within a ‘water curtain’.
Does submerged arc welding require gas?
Similar to MIG welding, SAW involves formation of an arc between a continuously-fed bare wire electrode and the workpiece. The process uses a flux to generate protective gases and slag, and to add alloying elements to the weld pool. A shielding gas is not required.