Submerged arc welding (SAW) is a well-established process that uses a continuous feed of a filler/electrode, melted by an electric arc between the electrode/filler and the work. Submersion refers to the hopper-fed flux powder that covers the weld path. This approach allows greater control and automation of straightforward welds. It reduces the direct need for operator skill, as the process—once established and validated—will be highly repeatable.
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This article will discuss submerged arc welding, its importance, how it works, its advantages and disadvantages, and the equipment used.
Submerged arc welding is a long-established, automated welding process in which an AC arc is formed between a heavy gauge workpiece and a continuously fed electrode. The arc is shielded by a directly deposited granular flux material of several possible varieties. This flux stream is fed over the weld zone to provide the exclusion of atmospheric contamination and a reducing environment. It also acts to contain some of the arc energy in the melt pool, enhancing weld quality and improving the application of energy. The non-adhesive, gravity-fed nature of the flux material implies a significant limitation—that only welding of upward-facing and close-to-horizontal seams is practical using SAW.
Submerged arc welding is commonly used for welding thick sections of steel, especially in applications such as shipbuilding, structural steel fabrication, pressure vessel manufacturing, and pipeline construction. It offers high deposition rates and throughput, deep penetration capabilities, excellent weld quality, and the potential for simple automation to reduce reliance on skilled labor.
The history of submerged arc welding originates in the early s when it was developed as a more reliable welding process that reduced the need for direct operational skills. The SAW process was initially developed by the National Tube Company (now part of the U.S. Steel Corporation) in the US. It was initially developed for welding longitudinal seams in pipes formed from rolled plates. The process involved using a bare electrode and a layer of flux powder to shield the arc and the weld pool. During World War II, SAW underwent significant improvements and gained wider acceptance, as a way to accelerate wartime production of ships and heavy military vehicles. The process was refined by the use of covered electrodes and the development of fluxes with more precisely tailored compositions and properties, improving the control over the weld pool and the metallurgical and crystalline properties of the resultant welds. In the s, SAW gained wide acceptance in industrial applications, due to process and quality developments. During the s–80s, further advancements included the development of more sophisticated fluxes with improved slag removal characteristics and enhanced chemical compositions. Automatic welding systems, including mechanized and robotic setups, were also introduced. Recent advancements have focused on optimizing process parameters, improving weld quality, and increasing throughput. The use of smarter power sources, CNC control systems, and optical monitoring techniques have greatly improved productivity and quality, keeping the process as a mainstay in heavy plate welding applications.
Submerged arc welding and arc welding are closely related welding processes that differ in several details. In SAW, the welding arc is submerged beneath a layer of granular flux, which shields the arc from the surrounding atmosphere. The flux serves multiple purposes, such as providing a protective shield, reducing spatter, and removing impurities. Arc welding refers to a broad category of welding processes in which the arc is shielded from the atmosphere by a variety of other means such as flux-coated filler rods, and blown or sealed atmospheric blankets.
SAW utilizes a granular flux material that is continuously deposited onto the melt pool. In arc welding, various methods can be employed, including gas tungsten arc welding (GTAW or TIG), gas metal arc welding (GMAW or MIG), and shielded metal arc welding (SMAW).
SAW is highly suited for automation and mechanization due to its tightly controlled process parameters. It is commonly used with CNC or robotic welding systems, whereby the electrode, flux delivery, and weld parameters can be precisely tuned and held stable. Arc welding processes can range from manual, handheld operations to semi-automated and fully automated systems. For more information, see our guide on What is Arc Welding?
The core purpose of SAW is to weld larger sections of steel quickly and repeatably. SAW is specifically suited for welding large structural parts, heavy-gauge plates, and components that require deep penetration into heavy sections.
SAW is a critically important manufacturing process with central relevance in various industries. SAW is particularly applicable to welding very thick sections of steel. It facilitates high throughput, allowing for the rapid processing of welding. Deep penetration capability makes SAW crucial when welding thick plates or components. It reliably produces high-quality welds with excellent mechanical properties. The low spatter levels and reduced risk of defects make this a widely relied-upon process.
SAW involves the formation of a steady and extremely high-power arc between a continuously fed electrode and the workpieces. The arc melts the edges of the workpieces and the filler rod, merging these into a single and consistent melt pool that is traversed along the weld path. Oxidation and weld-degrading inclusions are prevented by a reducing flux cover that is applied prior to the arc.
SAW is a process that can be established to be extremely repeatable. Its parameters and material options are adaptable to a wide range of applications. The general process steps of SAW are listed below:
The best method for executing a SAW process will be highly dependent on the materials, joint geometry, and quality requirements of the outcome. A stainless steel pressure vessel, for example, will have much higher quality expectations placed upon it than a dry gas pipeline.
SAW requires specific equipment to perform the welding process effectively. Here are the key equipment components used in SAW:
In SAW, a granular flux material is used to cover the arc and the weld pool. It is gravity deposited as a blanket over the active weld area. The flux serves several purposes, playing a crucial role in the welding process. Flux composition and properties vary depending on the application and the base metals being welded. Examples of flux are: basic (alkali) fluxes, acidic fluxes, neutral fluxes, and alloyed fluxes.
No, SAW does not benefit from gas shielding. Any gas supplied to encompass the weld would blow away the flux coating, with severely negative consequences.
SAW is primarily applied to high- and low-alloy content steels, including medium-carbon and stainless steel. Some materials used are listed below:
All of the readily weldable stainless steels can be joined using SAW. The process can also be applied to some difficult-to-weld alloys, with great care, some post-processing for stress relief, and minimization of inter-granular corrosion effects. To learn more, check out our guide on the Composition of Stainless Steel.
Carbon steels respond very well to SAW jointing, with few special concerns or limitations.
By careful control of flux and welding parameters, SAW can be applied to HSLA (high-strength low-alloy) steels with good results.
Solid solution nickel steel alloys respond well to SAW processing.
The strength of SAW jointing is reliant upon the properties of the parts being welded, the welding parameters used, the filler rod, flux selection, and optimization of the welding technique. When performed correctly with appropriate materials and techniques, SAW welds can achieve high strength levels. This is particularly true on thicker sections, for which its deep penetration enables single-pass welding, making significantly superior joints when compared with processes that require multiple passes.
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The minimum thickness for SAW can vary depending on various factors, including the specific application, welding parameters, joint design, and base metal composition. While there is no strict minimum thickness requirement for SAW, the process is most effective and efficient with welding materials that are at least 6 millimeters (0.24 inches) thick or more.
SAW is widely applied in various industries due to its productivity, high deposition rates, quality outcomes, and ability to weld thick sections of steel. Some industries that use it are:
Yes, SAW can be performed underwater, and it is known as underwater submerged arc welding (USAW) or wet welding. The process of USAW is similar to conventional SAW, but it involves additional material considerations and equipment to accommodate the underwater environment. USAW has its limitations and challenges compared to welding in dry environments. The presence of water can affect the weld quality, and additional precautions are necessary to mitigate the risks associated with working in underwater conditions.
SAW has advantages that make it a popular welding process in various industries. These include:
SAW also has some limitations and disadvantages. These include:
It depends. The setup cost of SAW can vary depending on several factors including: the specific application, application requirements, material, and welding parameters. While SAW has a relatively high initial setup cost, it can offer huge advantages in terms of productivity, efficiency, and weld quality that make it cost-effective for higher volume and more challenging tasks.
No, submerged arc welding (SAW) is generally considered to be relatively easier to learn compared to some other welding processes. Although SAW is considered relatively easy to learn compared with some welding techniques, it still requires effective training, experience, and adherence to safety protocols.
SAW and shielded metal arc welding (SMAW or stick welding) are related welding processes that have distinct characteristics and application differences. In SAW, the arc is formed between a continuously fed bare wire or tube electrode and the workpiece. The arc is shielded by an overlay of granular flux. Shielded metal arc welding (SMAW), on the other hand, uses a flux-coated electrode, which melts during welding, creating a shielding gas and reducing slag to protect the weld pool. In SAW, the arc is submerged under the layer of flux, making it difficult to directly observe the weld pool. The SMAW arc is visible as it is formed between the electrode and the workpiece. The welder can visually monitor the arc and the weld pool, allowing adjustments to be made throughout the process.
SAW is really only suited to flat and horizontal welding positions, as the molten metal will sag or drip when not guided into the weld by gravity. SMAW can be performed in various positions, including flat, horizontal, vertical, and overhead when performed with highly developed skills.
This article presented submerged arc welding, explained it, and discussed its purpose and how it works. To learn more about submerged arc welding, contact a Xometry representative.
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Submerged arc welding (SAW) is a common arc welding process. The first SAW patent was taken out in . The process requires a continuously fed consumable solid or tubular (metal cored) electrode.[1] 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.[2]
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[2] (although horizontal groove position welds have been done with a special arrangement to support the flux). Deposition rates approaching 45 kg/h (100 lb/h) have been reported — this compares to ~5 kg/h (10 lb/h) (max) for shielded metal arc welding. Although currents ranging from 300 to A are commonly utilized,[3] currents of up to 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 used, 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.
It feeds flux and filler metal to the welding joint. The electrode (filler metal) gets energized here.
It stores the flux and controls the rate of flux deposition on the welding joint.
The granulated flux shields and thus protects molten weld from atmospheric contamination.[2] The flux cleans weld metal and can also modify its chemical composition. The flux is granulated to a definite size. It may be of fused, bonded or mechanically mixed type. The flux may consist of fluorides of calcium and oxides of calcium, magnesium, silicon, aluminium and manganese compounds.[citation needed] Alloying elements may be added as per requirements. Substances involving large amounts of gas during welding are never mixed with the flux. Flux with fine and coarse particle sizes are recommended for welding heavier and smaller thickness respectively.
SAW filler material usually is a standard wire as well as other special forms. This wire normally has a thickness of 1.6 mm to 6 mm (1/16 in. to 1/4 in.). 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.[4] The electrode composition depends upon the material being welded. Alloying elements may be added in the electrodes. Electrodes are available to weld mild steels, high carbon steels, low and special alloy steels, stainless steel and some of the nonferrous of copper and nickel. Electrodes are generally copper coated to prevent rusting and to increase their electrical conductivity. Electrodes are available in straight lengths and coils. Their diameters may be 1.6, 2.0, 2.4, 3, 4.0, 4.8, and 6.4 mm. The approximate value of currents to weld with 1.6, 3.2 and 6.4 mm diameter electrodes are 150–350, 250–800 and 650– amps respectively.
The flux starts depositing on the joint to be welded. Since the flux is not electrically conductive when cold, the arc may be struck either by touching the electrode with the work piece or by placing steel wool between electrode and job before switching on the welding current or by using a high frequency unit. In all cases the arc is struck under a cover of flux. Flux otherwise is an insulator but once it melts due to heat of the arc, it becomes highly conductive and hence the current flow is maintained between the electrode and the workpiece through the molten flux. The upper portion of the flux, in contact with atmosphere, which is visible remains granular (unchanged) and can be reused. The lower, melted flux becomes slag, which is waste material and must be removed after welding.
The electrode is continuously fed to the joint to be welded at a predetermined speed. In semi-automatic welding sets the welding head is moved manually along the joint. In automatic welding a separate drive moves either the welding head over the stationary job or the job moves/rotates under the stationary welding head.
The arc length is kept constant by using the principle of a self-adjusting arc. If the arc length decreases, arc voltage will increase, arc current and therefore burn-off rate will increase thereby causing the arc to lengthen. The reverse occurs if the arc length increases more than the normal.[5]
A backing plate of steel or copper may be used to control penetration and to support large amounts of molten metal associated with the process.
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