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Submerged Arc Welding (SAW) is a common arc welding process. Originally devolved by the Linde - Union Carbide Company. It requires a continuously fed consumable solid or tubular (flux 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 SMAW (shielded metal arc welding) process.

SAW is normally operated in the automatic or mechanized mode, however, semi-automatic (hand-held) SAW guns with pressurized or gravity flux feed delivery are available. The process is normally limited to the Flat or Horizontal-Fillet welding positions (although Horizontal Groove position welds have been done with a special arrangement to support the flux). Deposition rates approaching 100 lb/h (45 kg/h) have been reported — this compares to ~10 lb/h (5 kg/h) (max) for shielded metal arc welding. Although Currents ranging from 300 to 2000 A are commonly utilized,¹ currents of up to 5000 A have also been used (multiple arcs).

Single or multiple (2 to 5) electrode wire variations of the process exist. SAW strip-cladding utilizes a flat strip electrode (e.g. 60 mm wide x 0.5 mm thick). DC or AC power can be utilized, and combinations of DC and AC are common on multiple electrode systems. Constant Voltage welding power supplies are most commonly used, however Constant Current systems in combination with a voltage sensing wire-feeder are available.

Electrode

SAW filler material usually is a standard wire as well as other special forms. This wire normally has a thickness of 1/16 in. to 1/4 in. (1.6mm to 6mm). In certain circumstances, twisted wire can be used to give the arc an oscillating movement. This helps fuse the toe of the weld to the base metal.²

Key SAW process variables

Other factors

Material applications

Advantages

· Practically no edge preparation is necessary · The process is suitable for both indoor and outdoor works. · Distortion is much less. · Welds produced are sound, uniform, ductile, corrosion resistant and have good impact value. · Single pass welds can be made in thick plates with normal equipment. · The arc is always covered under a blanket of flux, thus there is no chance of spatter of weld.

Limitations

Underwater welding

Underwater welding refers to a number of distinct welding processes that are performed underwater and should not be confused with the SAW process.³⁴ The applications of underwater welding are diverse—it is often used to repair ships, offshore oil platforms, and pipelines. Steel is the most common material welded.

The two main categories of underwater welding techniques are wet underwater welding and dry underwater welding, both are classified as hyperbaric welding.

For deepwater welds and other applications where high strength is necessary, dry underwater welding is most commonly used. Research into using dry underwater welding at depths of up to 1000 m are ongoing.⁵ In general, assuring the integrity of underwater welds can be difficult (but is possible using various nondestructive testing applications), especially for wet underwater welds, because defects are difficult to detect if the defects are beneath the surface of the weld.

Dry

In dry underwater welding the weld is performed at the prevailing pressure in a chamber filled with a gas mixture sealed around the structure being welded. For this process, gas tungsten arc welding is often used, and the resulting welds are of high integrity.

For the structures being welded by wet underwater welding, inspection following welding may be more difficult than for welds deposited in air. Assuring the integrity of such underwater welds may be more difficult, and there is a risk that defects may remain undetected.

Wet

Risks

The risks of underwater welding include the risk of electric shock to the welder. To prevent this, the welding equipment must be adaptable to a marine environment, properly insulated and the welding current must be controlled. Commercial divers must also consider the safety issues that normal divers face; most notably, the risk of decompression sickness following saturation diving due to the increased pressure of inhaled breathing gases.⁶ Another risk, generally limited to wet underwater welding, is the buildup of hydrogen and oxygen pockets, because these are potentially explosive. Many divers have reported a metallic taste that is related to the breakdown of dental amalgam.⁷⁸⁹ There may also be long term cognitive and possibly musculoskeletal effects associated with underwater welding.¹⁰

References

^ Kalpakjian, Serope, and Steven Schmid. Manufacturing Engineering and Technology. '5th ed'. Upper Saddle river, NJ: Pearson Prentice Hall, 2006.
^ Jeffus, Larry. Welding: Principles and Applications. Florence, KY: Thomson Delmar Learning, 2002.
^ Keats, DJ (2005). Underwater Wet Welding - A Welder's Mate, Speciality Welds Ltd. ISBN 1-899293-99-X., http://www.specialwelds.com.
^ ^a ^b ^c ^d Cary, HB and Helzer, SC (2005). Modern Welding Technology. Upper Saddle River, New Jersey: Pearson Education. pp.677-681. ISBN 0-13-113029-3.
^ Bennett PB, Schafstall H (July 1992). "Scope and design of the GUSI international research program". Undersea Biomed Res 19 (4): 231–41. PMID 1353925, http://archive.rubicon-foundation.org/2596. Retrieved on 5 July 2008.
^ US Navy Diving Manual, 6th revision. United States: US Naval Sea Systems Command. 2006, http://www.supsalv.org/00c3_publications.asp?destPage=00c3&pageID=3.9. Retrieved on 5 July 2008.
^ Ortendahl TW, Dahlén G, Röckert HO (March 1985). "Evaluation of oral problems in divers performing electrical welding and cutting under water". Undersea Biomed Res 12 (1): 69–76. PMID 4035819, http://archive.rubicon-foundation.org/3030. Retrieved on 5 July 2008.
^ Ortendahl TW, Högstedt P (November 1988). "Magnetic field effects on dental amalgam in divers welding and cutting electrically underwater". Undersea Biomed Res 15 (6): 429–41. PMID 3227576, http://archive.rubicon-foundation.org/2486. Retrieved on 5 July 2008.
^ Ortendahl TW, Högstedt P, Odelius H, Norén JG (November 1988). "Effects of magnetic fields from underwater electrical cutting on in vitro corrosion of dental amalgam". Undersea Biomed Res 15 (6): 443–55. PMID 3227577, http://archive.rubicon-foundation.org/2485. Retrieved on 5 July 2008.
^ Macdiarmid JI, Ross JAS, Semple S, Osman LM, Watt SJ, Crawford JR (2005). "Further investigation of possible musculoskeletal and cognitive deficit due to welding in divers identified in the ELTHI diving study". Health and Safety Executive Technical Report rr390, http://www.hse.gov.uk/research/rrpdf/rr390.pdf. Retrieved on 5 July 2008.

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