Table of Contents
Submerged Arc welding is a more specific niche to arc welding where two metals are joined together by using an arc that is formed using a continuously fed electrode and it must be already used to weld on the workpiece that you are dealing with currently. The shielding gas for protection is provided by a layer of powdered flux and slag that protects the weld zone.
This is a well-established and refined form of welding which requires minimal amounts of shielding gas. The arc is submerged between the flux layers and hence isn’t visible enough during the welding process. When we talk about the electrode used here, there are various types used as it can be solid, cored wire, or strip wire made from sintered materials.
The flux is made by forming a glassy slag by agglomerating the constituents using the ‘binder and corning’ process. Many welders and other enthusiasts have this very common question. Is SAW an automatic/mechanized process? The answer is ‘yes’, SAW is usually operated as a mechanized process. Just like other welding processes, bead shape and performance are dependent on the welding current supplied, arc voltage, and travel speed.
One can gain additional productivity in this welding process by using a small diameter of non-conducting wire into the edge of the welding pool that is at the leading end. This has shown weld deposition rates increased to about 20% distinctively.
One more trick to get better deposition rates is by replacing the wire used with a 0.5mm thick strip that is 60mm wide as it can be used for surface components easily. This type of SAW welding is ideal for longitudinal and circumferential welding which deals with the manufacture of lie pipes and pressure vessels.
History
Submerged arc welding was first invented and got its patent in the year 1935 and back then, granulated flux was placed over the electric arc. It was developed by the E O Paton Electric Welding Institute located in Kyiv, Ukraine. It was invented back then for the manufacture of the T34 Tank using for warfare in the Second World War.
Key Elements
Welding Head
The welding head helps in feeding the flux and filler metal to the welding joint and this is the region where the filler metal gets refilled (energized).
Flux hopper
As the name suggests, it is a store-house of all the flux used and controls the rate of flux deposition on the welding joint.
Flux
Granulated flux shields are used here which not only provide efficiency to the welding joints but also protect the molten weld from any sort of atmospheric contamination. More than just cleaning and purifying the weld, it also modifies the chemical composition of the weld.
The flux has a compositional mixture of fluorides of calcium and oxides of calcium, magnesium, silicon, and aluminum as well as manganese. The basic recommendation while using flux for welding is to have a fine texture with coarse particle sizes for heavier as well as smaller thicknesses respectively.
Electrode
The electrode used for SAW is of many types as mentioned earlier. Whatever be the types of wires used, it has a thickness of around 1.6mm to 6mm. Twisted wires used in this case offer oscillation in the welding process. We basically fuse the toe of the weld to the base of the metal and the electrode used here has the constituents just like the weld metal.
These electrodes are compatible with alloy steels, mild steels, high-carbon steels, stainless steel, and some copper and nickel metals too. Copper-coated electrodes provide better electrical conductivity and more resistance towards rust and corrosion. The approximate value of currents to weld with 1.6mm, 3.2-mm, and 6.4-mm diameter electrodes are 150–350, 250–800, and 650–1350 Amps respectively.
Working Process
Just like MIG or GMAW welding, this is a wire-fed welding process where the wire is fed through a torch which is moved along the welding joint by machines. Setting up the welding machine is quite simple and much similar to the other processes.
The voltage supplied determines the bead width, and amperage influences the penetration of the welding torch and deposition rates.
This arc welding process relies on granular flux that protects the weld from atmospheric hazards and the arc here is buried in the flux and is not visible during the welding process. Once the arc, flux, and base metal form the weld pool.
Equipment
Investing in proper equipment, a good amount of power supply, and a wire feeder, helps us achieve some good results in this field. Several accessories are available and, in some applications, the torch is kept stationary and the workpiece is moved using positioning equipment.
- SAW tractors are used for arc motion due to its increased portability and flexibility for work where welding can be brought to a shop or a remote workplace.
- Side beams and gantry setups are also used which work in a fixed position and every time welding work is to be done or completed, it must be brought to the weld cell. The setup process is very low but the portability is negligible here.
- Girth welding for storage vessels and circular welders for attaching nozzles can be used. For more geometric welding equipment like pipe saddles, positioning equipment is more feasible.
SAW welding is possible only in two positions for good deposition rates and high-current parameters which are flat and horizontal positions.
Joint tracking equipment helps in viewing the arc while welding which is normally not possible. Simple tracking mechanisms include lasers to more advanced mechanisms like the tactile probe.
Ideal Parts
- Joint and Part Geometries: SAW is compatible with straight-line joints because it requires more complex and expensive machining to perform repeated parts with jogs in the weld. SAW is better suited for high-volume components, which does not mean it is more accurate in the same part.Job shops can also take advantage of technology. The components do not need to be identical, but they must have the same geometry to enhance the process. For example, it is common for both SAW and equipment to easily weld 3.7-meter-diameter and 3-meter-diameter.
Since the pressure vessels are geometrically identical. The idea is to find parts that can use the same arc and work-speed equipment and placement to minimize shifts and, therefore, timeliness.
- Long weld joints: One disadvantage of SAW is the need for interphase cleaning. For this reason, it is best for long weld joints (often 1.2 m or more), which can be cleaned during welding.With smaller welds, multi-tasking is more difficult because of the amount of time spent on cleaning, and the proportion of repositioning and re-installation of spent equipment becomes smaller. As a side note, it is also important to invest in flux recovery and reconditioning equipment (vacuum and oven) to reduce investment costs.
- Welder welders with diameters larger than 200 mm: SAW is a popular choice in a pressure vessel and pipe applications because vessels or pipes can be mounted at the position. But less than 200 mm in diameter.Flux prevention becomes more difficult as the flux is stopped from the pipe. Since the weld cooling rate in SAW is slower than other processes, the use of smaller diameter pipes may also lead to an unacceptable bead profile.
- Good Access Components: SAW equipment is heavy, which makes space and part of it important. The system may need to be custom-designed for use in small spaces, but wire feeding becomes a problem. Larger articles are not as flexible as the smaller articles used only in the robotic GMAW branch.
Key SAW Process Variables
- Wire feed speed
- Arc voltage
- Travel speed
- Electrode Stick-Out
- Polarity and current type (AC or DC) and variable balance AC current
- Material Applications
- Carbon steels (structural and vessel construction)
- Low alloy steels
- Stainless Steels
- Nickel-based alloys
- Surface applications (wear, build and corrosion-resistant overlapping of steels)
- High deposition rates (45 kg per hour (100 lb / h) are reported).
- High operating factors in mechanical applications.
- The arc is always covered under a blanket of flux, so there is no chance of the weld being dispersed.
- Deep Weld Penetration.
- Sound welds are readily manufactured (with good process design and control).
- High-speed welding of thin sheet steels up to 5 m / min (16 ft/min) is possible.
- Minimal welding fume or arc light is released.
- There is practically no need for edge preparation due to the joint configuration and the required penetration.
- This process is suitable for indoor and outdoor activities.
- Welds produced are sound, uniform, elastic, corrosion-resistant, and have good impact value.
- Single pass welds can be made in thick plates with simple equipment.
- 50% to 90% of the flux can be recycled, recycled, and reused.
- Limited to ferrous (steel or stainless steel) and some nickel-based alloys.
- Generally limited to 1F, 1G, and 2F locations.
- Usually limited to long straight joints or rotated pipes or ducts.
- Relatively troublesome flux management systems are required.
- Flux and slag residue pose a health and safety concern.
- Inter-pass and post-weld slag removal required.
- Backing strips are essential for proper root penetration.
- Limited to high-thickness materials
FAQ
1. Why is submerged arc welding referred to as submerged?
Submerged Arc Welding (SAW) is named as such because the weld pool and arc using which weld is done, is present in the underlying layers of the flux blanket. The flux layers become molten and get conductive allowing current to pass between the electrode and the workpiece.
2. Is the submerged arc welding process automatic?
Submerged Arc Welding (SAW) is fully automatic as well as semi-automatic based on the equipment used. The arc is flat and is maintained between the end of the wire electrode and the weld. The electrode is fed into the arc as it is melted.
In automatic submerged arc welding, three different types of welding are used which are flux delivery gun, deep groove gun, and concentrated flux delivery gun. Moreover, SAW welding is accomplished by using a set of drive rollers that are run by a controlled automatic motor.
3. What is submerged arc welding? When was it invented?
Submerged Arc Welding (SAW) is a specialized type of arc welding where a continuously fed solid or tubular electrode is used to form the arc between the two metals to be joined. It was first patented by Jones, Kennedy, and Rothermund in the year 1935, where they covered an electric arc beneath a bed of granulated flux.
4. What type of electrode is used in submerged arc welding?
SAW filler wire/ electrode is generally a normal wire where it can be a solid wire, strip wire, or even a cored wire. The wire thicknesses range from 1.6mm to 6mm straight where twisted wires are used for providing an oscillating movement in the arc. The electrode has a composition more similar to the metal to be weld and requires alloying for more durability.
5. What is the major function of the coating on the arc welding electrode?
The coating given on the arc electrode is termed as ‘flux’ as it has a mixture of fluoride of calcium and oxides of calcium, magnesium, silicon, and aluminum. This coating acts as a shielding layer to the weld pool from corrosion and rust from atmospheric moisture and oxygen. It also has additional filler metal that increases the deposition rates and reduces the fluidity of the weld pool.
6. Which type of Arc welding flux is susceptible to moisture pick-up?
Agglomerated submerged arc welding flux is susceptible to moisture pickup. It produces a smaller number of sparks and splatter are leaked more than other welding arc methods. This type of welding minimizes the errors caused by humans ourselves.
7. What are the advantages and some limitations that SAW welding has?
- 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
- Not very portable
- The process may be limited to flat or horizontal-fillet welding positions
- Limited to steel/stainless steel, and some nickel-based alloys
- Best for long straight seams or rotated pipes or vessels
- Requires flux handling systems
- Requires post-weld slag removal
- Best for thicker materials
Sean Coby is a welder par excellence and well respected among the welding community in Woodbridge, VA. He prides himself to be the fabricator and mechanic in the automotive/ diesel industry for the past more than eight years now. As the chief editor of his https://weldinginfocenter.com, he shares his experience to be safe during welding and to take proactive steps for becoming a successful welder like him.