What is Submerged Arc Welding (SAW)?
Submerged Arc Welding (SAW) is a joining process that utilizes the establishment of an electric arc between a continuously fed electrode and a workpiece to be welded.
The arc is surrounded by a blanket of powdered flux used to supply electrical conduction between the coated metal to be joined and the electrode when in the molten state.
The first patent for SAW was obtained in 1935. In SAW, the process relies on the delivery of a continuously fed consumable solid or tubular (metal-cored) electrode.
The weld mass and arc zone are protected from contamination by atmospheric gases because the process is carried out “under” a blanket of granular fusible flux, made up of lime, silica, manganese oxide, calcium fluorite, and various other compound elements.
When this flux turns molten, it becomes conductive and provides a current path between the electrode and the work. An ample layer of flux can be used to provide extensive coverage of the molten metal, preventing slag and spatter, but also preventing the extreme ultraviolet radiation and fumes present in shielded metal arc welding (SMAW).
How Does Submerged Arc Welding Work?
Submerged-arc welding (SAW) is one of the most recognized, arc welding processes characterized by the generation of an arc developed between a continuously fed electrode and a work piece and a powdered blanket of flux that creates a protective gas shield and slag (may also provide alloying elements to the pool).
There is no shielding gas to require. With the arc submerged in the flux blanket, it is not typically visible during the welding process. There is extensive research surrounding this process and it can achieve a great deal of versatility.
There are solid or cored wires or a strip from a sheet of sintered material that is used for the electrode. The flux is either created by fusing constituents to achieve a glassy slag that can be crushed to powder or in some cases agglomerated with a binder in a corn process.
The chemical nature of the flux together with the size distribution works to stabilize the arc, and provide the mechanical properties of the weld metal and shape of the bead.
SAW is generally a mechanized process. The welding current (typically between 300 and 1000 amps), arc voltage and travel speed will impact the bead shape, penetration, and chemical composition of the deposited weld metal.
As the operator does not see the weld pool the parameters chosen and position of the of the filler wire will have a significant impact.
Although SAW is typically performed one wire and either AC or DC current there are several variations identified including using two or more wires, feeding cut wire into the gap before welding, and adding metal powder.
Using a non-conducting couple with a small diameter forward of the leading edge of the weld pool, increases productivity by deposition rates of up to 20%.
These variations of SAW are technologies are represented and used only in certain applications to improve productivity (through increasing either deposit rates and/or travel speed).
The wire can be replace with a strip (typically 60mm wide and .5 mm thick) enabling the process to used in surface or in component applications.
Submerged Arc Welding Applications
The applications of Submerged Arc Welding include the following
- Submerged Arc Welding is useful for welding pressure vessels such as boilers.
- Many structural configurations, pipes, earth-moving equipment, shipbuilding, railroad construction, and locomotives.
- This kind of welding can be used for the repair of 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 certain ferrous metals like stainless steel and steel
- It is limited to either long, straight seams, or rotated pipes and vessel
- Backing strips are required to achieve proper penetration
- It is limited to heavy 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.