Electroslag Welding vs Submerged Arc Welding: What’s the Difference?
In the world of industrial welding, choosing the right technique can significantly impact the quality and efficiency of your projects.…
Imagine a welding process that offers remarkably high deposition rates, minimal spatter, and deep weld penetration, all while operating at high speeds. This is the essence of Submerged Arc Welding (SAW), a technique that has revolutionized industries like shipbuilding, railroads, and wind turbine construction. But how exactly does this process work, and what makes it so advantageous? In this article, we’ll dive into the principles and mechanisms behind SAW, explore its various industrial applications, and weigh its benefits against its limitations. Are you ready to uncover the intricacies of this powerful welding method and see how it can transform your projects? Let’s get started.
Submerged Arc Welding (SAW) was developed in 1935 by the E. O. Paton Electric Welding Institute in Kyiv, Ukraine. This welding method gained significant attention during World War II, especially for producing the T34 tank. Its efficiency and reliability made it a vital process in wartime manufacturing and have continued to be important in industrial applications.
SAW involves creating an electric arc between a continuously fed consumable electrode and the workpiece. The arc and the molten weld pool are completely submerged under a blanket of granular fusible flux. The flux shields the molten weld from air, produces shielding gases and slag, and can add alloying elements to the weld pool. The entire process takes place beneath the flux layer, which helps to maintain the quality and integrity of the weld.
Flux: The flux in SAW is a granular material made of compounds like manganese, silicon, titanium, and calcium fluoride, playing a crucial role in the welding process. When molten, the flux becomes conductive and facilitates a current path between the electrode and the workpiece. It also cleans the weld, shapes the weld profile, and prevents oxidation.
Electrode: The electrode in SAW is typically a continuous solid or cored wire that is fed into the weld pool from a spool. The choice of electrode diameter depends on the specific welding application and desired weld characteristics.
Arc: The electric arc is the heat source in SAW, generated between the electrode and the metal workpiece. Due to the flux layer, the arc is not visible during the welding process, which helps to minimize spatter and improve safety.
SAW is generally limited to flat and horizontal positions because of the fluidity of the weld pool and the molten slag. This characteristic makes it unsuitable for vertical or overhead welding. The process can be fully mechanized or semi-automatic, which allows for high productivity and consistent weld quality. Key parameters such as welding current, arc voltage, and travel speed must be carefully controlled to achieve optimal results.
High Deposition Rates: One of the major advantages of SAW is its ability to achieve high deposition rates, making it an efficient choice for welding thick, flat, or horizontal metal sections.
Clean Welds: The process creates welds with little spatter and no visible arc light, reducing the need for cleaning afterward. The flux layer ensures a smooth and clean weld with minimal fume generation.
Thermal Efficiency: SAW boasts a high thermal efficiency of up to 60%, which is significantly higher than other welding processes like manual metal arc welding.
SAW is widely used in industries needing thick, consistent welds. It is particularly effective for longitudinal and circumferential butt and fillet welds. Common applications include shipbuilding, automotive manufacturing, and the railroad industry. Its ability to produce high-quality welds in low-medium carbon steels, low alloy-high strength steels, tempered steels, quenched steels, and stainless steels makes it a versatile welding process for various industrial sectors.
A typical SAW setup includes a power source, flux hopper, wire feed mechanism, and electrodes. The power source must provide a constant current to generate the necessary heat for welding. Proper setup and calibration of these components are essential for achieving high-quality welds.
Submerged Arc Welding remains a robust and efficient welding process, leveraging the protective properties of flux to produce high-quality, consistent welds with minimal spatter and fume generation. Its diverse applications and high productivity make it a crucial method in various industrial sectors.
Submerged Arc Welding (SAW) is a highly efficient process that uses an electric arc to join metals.
The core principle of SAW involves forming an electric arc between a continuously fed bare metal electrode and the workpiece. This arc generates the necessary heat to melt the surface of the base metal and the end of the electrode, creating a molten weld pool that joins the metals. The granular flux plays a pivotal role by remaining non-conductive when cold but becoming conductive as it melts near the arc. This maintains electrical conductivity, protects the weld from atmospheric contamination, and purifies and fortifies the weld.
The SAW process employs a range of specialized equipment to ensure efficient welding:
To initiate the welding process, the arc is struck by touching the electrode to the base metal or using alternative methods like steel wool or high-frequency current. Once the arc is established, the flux near the arc melts and becomes conductive, sustaining the arc.
The molten metal from the electrode travels through the arc to the workpiece. There, it solidifies to form the weld. The flux in proximity to the arc intermixes with the molten weld metal, enhancing the quality of the weld by purifying and fortifying it. The flux also forms a glass-like slag that floats on the weld’s surface, providing a protective cover that can be removed and reused.
SAW can operate with either direct current (DC) or alternating current (AC).
SAW is most effective in flat and horizontal positions due to the fluid nature of the molten metal and slag, which cannot be easily maintained in vertical or overhead positions. The process is suitable for welding various materials, including:
SAW offers several advantages over other welding processes:
By understanding the principles and processes of Submerged Arc Welding, operators can leverage its benefits to achieve efficient, high-quality welds across various industrial applications.
Submerged Arc Welding (SAW) uses an electric arc between a continuously fed wire electrode and the workpiece to generate the heat needed for welding. This electric arc produces intense heat, which melts both the electrode and the base metal, forming a molten weld pool that solidifies to create a strong bond.
The granular flux covering the arc and weld pool plays several essential roles:
The electric arc generates intense heat, reaching up to 6,500°F (3,600°C). This heat melts the end of the electrode and the base metal’s surface, creating a molten weld pool necessary for the welding process.
As the electrode melts, molten metal is transferred to the weld pool. The continuous feed of the electrode ensures a steady supply of molten metal, effectively filling the weld joint.
Initially, the granular flux is non-conductive. Upon melting near the arc, it becomes conductive, allowing the arc to be maintained under the flux blanket. This characteristic is crucial for sustaining a stable arc and achieving high-quality welds.
Key parameters to control in SAW include:
SAW can utilize both direct current (DC) and alternating current (AC):
SAW is primarily suited for flat and horizontal welding positions due to the fluid nature of the molten metal and slag. It is highly effective for welding materials such as low to medium-carbon steels, low alloy-high strength steels, tempered steels, quenched steels, and stainless steels.
In summary, Submerged Arc Welding involves generating an electric arc between a continuously fed electrode and the workpiece, with the arc and weld pool submerged under a protective blanket of granular flux. The flux not only shields the weld from contamination but also stabilizes the arc, forms a protective slag, and can enhance the weld’s properties through alloying. Proper control over welding parameters and the use of appropriate current and polarity configurations are essential for achieving high-quality welds in suitable positions and materials.
The shipbuilding industry relies heavily on Submerged Arc Welding (SAW) for joining large steel plates and sections. This process is crucial for constructing the hulls and other significant components of ships, offering deep penetration and high deposition rates to ensure strong, durable welds that can withstand harsh marine environments. Similarly, SAW is extensively used in offshore construction for fabricating platforms and pipelines. The deep, reliable welds produced by SAW are vital for structures exposed to challenging offshore conditions, ensuring the structural integrity of platforms and subsea pipelines.
In the fabrication of pressure vessels, SAW provides the necessary strength and reliability for thick-walled vessels, ensuring they can safely contain high-pressure contents. This is especially important in industries such as oil and gas, chemical processing, and power generation.
Pipeline construction benefits significantly from SAW due to its high deposition rates and the ability to create strong, long-lasting joints. The process is particularly effective for welding long pipelines, ensuring the integrity and durability necessary for transporting gases and liquids over extensive distances.
SAW is essential for joining beams, columns, and other components in bridges, buildings, and large infrastructures, ensuring robust and secure connections critical for structural integrity. Its capability to handle thick materials with deep penetration makes it a reliable choice for large-scale construction projects.
The heavy equipment manufacturing sector uses SAW to produce components for mining, construction, and agricultural machinery, ensuring the welds are strong and durable for demanding conditions. This guarantees that the machinery can withstand the rigorous environments in which they operate.
In the railcar manufacturing industry, SAW is employed to join various components such as underframes, sidewalls, and roofs. The reliability and efficiency of the process are essential for ensuring the safety and durability of railcars.
In the renewable energy sector, SAW is used to weld large sections of wind turbine towers. The process’s high deposition rates and deep penetration capabilities are advantageous for constructing these tall structures, ensuring their stability and longevity.
SAW is used in the construction of large storage tanks for liquids and gases. The process ensures the tanks are strong and leak-proof, which is essential for maintaining safety and operational efficiency in various industries.
With the rise of large-scale construction projects, SAW is increasingly applied in fabricating structural steel for schools, hospitals, and other public facilities. The process optimizes performance, increases efficiency, and enhances the precision and finishing quality of the welds.
Although not as dominant as in other sectors, SAW still plays a role in the automotive industry, particularly in sheet metal work and fabrication. The growing demand for electric vehicles is expected to further boost the use of SAW in this sector.
Submerged Arc Welding (SAW) is known for producing welds with superior mechanical properties and high quality. The process ensures deep penetration and uniform heat distribution, enhancing the toughness and strength of the welds. The protective flux layer plays a crucial role by preventing contamination and oxidation, resulting in a strong metallurgical bond between the welded materials.
SAW is highly efficient, boasting a high deposition rate that allows for more weld material to be applied in less time compared to traditional welding methods. This efficiency is particularly beneficial in large-scale industrial projects, as the continuous feed of the electrode wire enables long, uninterrupted welds, minimizing the need for frequent stops to replace electrodes.
The SAW process enhances safety in the welding environment. The flux blanket reduces harmful fumes and UV radiation, making the workspace safer for welders. Additionally, the absence of spatter, arc flash, and radiation exposure further contributes to a safer working environment.
SAW is well-suited for automation, which reduces the need for manual labor and ensures consistent welding conditions. This automation leads to high throughput without compromising the quality of the welds. The process’s automated nature is crucial for maintaining consistent weld quality, especially in high-production environments.
One significant advantage of SAW is its minimal thermal distortion, which is crucial for maintaining the integrity and strength of welds in thick materials. The uniform heat distribution and controlled cooling rates help in achieving minimal distortion.
SAW is versatile and can be used for both indoor and outdoor applications. It is capable of handling various material thicknesses, including thin sheet steels at high speeds. This versatility makes it suitable for a wide range of industrial applications, from shipbuilding to heavy equipment manufacturing.
Despite its advantages, SAW has certain material restrictions. It is primarily limited to welding ferrous materials such as steel, stainless steel, and some nickel-based alloys. It is not suitable for welding non-ferrous metals like aluminum, magnesium, zinc alloys, or cast iron.
SAW is generally suitable only for flat, horizontal, and vertical welding positions, and welding in other positions requires special devices to ensure proper flux coverage. This limitation can be a drawback in applications requiring more flexibility in welding positions.
The handling of flux in SAW can be relatively cumbersome. The flux and slag residues generated during the process need to be carefully managed and removed after welding. These residues can present health and safety concerns if not properly handled.
One of the challenges with SAW is that the welder cannot directly observe the arc and the groove during welding. This necessitates the use of automatic welding seam tracking devices to ensure proper alignment and prevent welding deviations. The lack of visibility can complicate the welding process.
SAW typically uses a large current, which can pose challenges in maintaining arc stability, especially when the current is less than 100A. This makes SAW unsuitable for welding thin-walled pipes, where precise control over the arc is necessary.
Implementing SAW often requires specialized equipment. This includes robots capable of holding the wire feed and flux, as well as a large power supply to handle the high welding currents. The need for such specialized equipment can increase the initial setup costs and complexity.
Submerged Arc Welding (SAW) needs powerful sources that can deliver high currents, usually between 300 and 1500 amperes. These power sources must be rated for a 100 percent duty cycle due to the continuous nature of SAW operations. Both generator and transformer-rectifier power sources are used, with rectifier machines being more popular. For high-current applications, multiple rectifier machines can be connected in parallel to provide the necessary power.
Wire feeders and control systems are essential for maintaining a consistent feed of the electrode wire.
SAW can be performed using single or tandem (multi-wire and multi-arc) welding heads. Tandem systems can include up to six welding arcs and multi-wire heads capable of using up to four wires. These configurations are particularly useful for deep groove and narrow gap applications. Modern welding heads and torches often feature advanced control systems, including touch screen interfaces for monitoring data and adjusting parameters.
Flux is crucial in SAW as it protects the weld pool and stabilizes the arc. It can be fed manually or with a hopper, and flux recovery systems help reduce waste and cost. This system collects and reuses the flux, reducing waste and improving cost-effectiveness.
For automatic welding, travel mechanisms such as sub arc tractors and weld positioning equipment are used. These devices move the welding system or the workpiece, ensuring consistent welds over long distances. The use of such equipment is crucial for maintaining uniform weld quality in automated processes.
Advanced robotic SAW systems enhance precision and efficiency. They feature integrated torch designs with streamlined flux delivery, allowing for precise robotic welding on complex paths, including corners and variations. Digital inverter-based power sources with software-driven waveform control technology enable precise control over the arc process, further enhancing weld quality.
Modern SAW systems incorporate digital process control technology, which allows for increased weld speeds, higher quality welds, and improved efficiencies. These systems enable subtle waveform changes for precise control of the submerged arc deposition rate and penetration, optimizing the welding process.
Automation in SAW extends to multi-arc and multi-wire systems, where a central console can control up to six weld heads. These systems allow for the saving and downloading of welding parameters, providing ergonomic hand-held pendants for operators to observe the weld and adjust parameters in real-time.
Automated SAW systems significantly reduce operator fatigue, increase welding speed, and deliver smooth, uniform welds. This automation minimizes the need for manual adjustments to maintain arc stability. Additionally, automated systems enhance workplace safety and cleanliness by reducing spatter and fumes, thus maximizing output and minimizing rework costs.
The power source is essential in SAW, supplying the electrical energy needed to create and sustain the welding arc. It can be either a constant voltage or a constant current type, depending on the specific application. A power source rated for a 100 percent duty cycle is crucial, as SAW operations are often continuous and lengthy.
The wire feeder delivers the electrode wire to the welding arc at a controlled speed. There are two main types: the voltage-sensing wire feeder, which adjusts the speed based on welding voltage, and the fixed speed wire feeder, commonly used in constant voltage systems.
The welding torch or gun holds the electrode wire and directs it toward the welding joint. In automatic welding, the torch is attached to the wire feed motor and includes current pickup tips. For semiautomatic welding, a welding gun and cable assembly are used.
The flux hopper stores and delivers the granular flux to the weld joint by gravity. The flux melts due to the arc’s heat, forming a protective slag over the weld pool and generating shielding gases that protect the weld from atmospheric contamination.
To start the arc in SAW, you can either touch the electrode to the base metal or use high-frequency current with steel wool under the flux.
During the welding operation, the electrode wire is continuously fed into the arc, transferring melted metal to the workpiece. The molten flux intermingles with the molten metals, forming a slag that shields the weld and enhances its quality.
SAW can be applied using different methods:
SAW is typically limited to flat and horizontal fillet positions due to the fluid nature of the molten pool and slag. However, under controlled procedures, welding can also be performed in the horizontal position (3 o’clock welding). Vertical and overhead positions are generally not feasible because the molten metal and flux cannot be effectively held in place.
The power source and controls are critical for setting welding parameters such as amperage, voltage, and travel speed. Since the arc is submerged and not visible, operators must accurately set these parameters without direct visual feedback.
For automatic welding, a travel mechanism is employed to move the torch along the weld joint, ensuring consistent and precise welding. This mechanism is essential for maintaining uniform weld quality over long distances.
SAW provides significant health and safety advantages. The submerged arc reduces the risk of "arc eye" and minimizes fume generation, creating a safer working environment for operators.
The selection of consumables, such as the electrode (solid wire, cored wire, or strip) and flux, is critical. These consumables, along with parameters like amperage, voltage, and travel speed, must be chosen carefully to meet the specific design objectives of the weld.
Even with automation, operators often need to closely monitor weld parameters during the Submerged Arc Welding (SAW) process. This proximity poses a risk of electrical shock, especially in wet, damp, or humid environments, which can reduce skin resistance and the insulating properties of protective gear. Implementing weld cameras allows operators to monitor the process from a safe distance, significantly reducing the risk of electrical hazards.
SAW produces fewer welding fumes and ultraviolet radiation compared to other methods, thanks to the protective granular flux. The flux helps trap fumes and block UV radiation, reducing exposure to airborne contaminants and harmful radiation. Ensuring proper ventilation in enclosed or indoor settings is crucial to maintain a safe working environment.
Monitoring the welding process in cramped or elevated positions can cause discomfort for operators. Using remote monitoring systems, such as weld cameras, can help alleviate this issue by allowing operators to work from more ergonomic and safe locations.
SAW, like all welding processes, involves several safety risks. When welding in enclosed or confined spaces, the risk of electrocution and fire hazards increases due to limited air volume and potential interactions with solvents or other substances. It is essential to assess confined spaces for hazards such as chlorinated hydrocarbons, low air volume, high moisture, and flammable materials before starting the welding process.
The presence of flammable materials in confined spaces can lead to fires if not properly managed. Operators must wear fireproof apparel to prevent burns from molten slag and consider the direction of slag flow. Additionally, the presence of conductive elements near the weld area poses a risk of accidental electrical contact.
Although SAW produces fewer fumes than some other welding methods, the particulate matter and gases emitted can still impact air quality. These particles can travel far, contributing to haze or smog and posing health risks to humans and animals. Gases produced during welding, such as nitrogen oxides and ozone, can also contribute to ground-level ozone formation, a component of smog.
Welding fumes can harm local ecosystems. Particles can contaminate water sources and soil, affecting aquatic life and plant growth. Heavy metals like chromium and nickel in the fumes are toxic and can harm flora and fauna. Additionally, the gases produced can lead to acid rain, altering the pH of soil and water bodies, disrupting sensitive ecosystems.
Compared to manual metal arc welding, SAW generally has a lower environmental impact. The use of granular flux in SAW reduces fume emissions, making it a more environmentally friendly option. This reduction in emissions helps minimize the process’s impact on global warming, acidification, and eutrophication.
The shipbuilding industry relies on Submerged Arc Welding (SAW) for its efficiency in welding thick materials. SAW plays a vital role in constructing ship hulls and other large marine vessels. By creating strong welds, it ensures the durability and structural integrity of these heavy-duty structures. Similarly, in manufacturing, SAW is used to weld industrial cans, vessels, and other large equipment. The process produces robust, clean welds with minimal post-weld cleaning, making it an attractive option for automated production lines.
In the realm of construction, particularly for bridges and large infrastructure projects, SAW proves invaluable. Its ability to weld thick materials with precision minimizes the risk of distortion, maintaining the integrity of critical structures. This method is ideal for welding pressure vessels and significant structural components, meeting the rigorous demands of infrastructure projects. Similarly, in the manufacturing sector, SAW is valued for producing strong, clean welds that enhance productivity and quality.
SAW is also effective for surfacing and overlay applications, such as wear-facing and corrosion protection of steels. By depositing a layer of weld metal on the surface, it enhances the material’s durability and resistance to wear and corrosion. This capability is crucial for applications that demand improved surface properties and longevity.
SAW is particularly advantageous for welding large rotating pipes and vessels. Its high productivity and ability to create long, straight seams make it ideal for pipeline construction and maintenance. The process’s automation ensures consistent, high-quality welds, which are essential for the reliability and safety of pipelines.
A noteworthy case study in a shipyard demonstrated how automation of SAW processes significantly boosted productivity. Automated SAW systems, integrated with welding tractors and flux recovery systems, were employed to weld a ship’s hull, leading to reduced labor costs and increased efficiency. Another case study in bridge construction highlighted SAW’s ability to provide deep penetration and strong welds in thick structural steel, ensuring the bridge’s structural integrity while adhering to tight deadlines.
By effectively managing these challenges, SAW continues to be a highly efficient welding technique for various industrial applications.
Below are answers to some frequently asked questions:
The submerged arc welding (SAW) process works by forming an electric arc between a continuously fed electrode and the workpiece, both of which are protected by a layer of granular flux. The flux creates a protective gas shield and slag that prevent atmospheric contamination, ensuring a clean weld. The intense heat generated by the arc melts the base material and the filler wire, which fuse together to form the weld bead. This process is typically mechanized or automated, with parameters like welding current, arc voltage, and wire feed speed being set based on the metal type and desired weld properties.
Submerged Arc Welding (SAW) is widely used across various industries due to its efficiency and high-quality welds. Main applications include shipbuilding for large vessels and offshore rigs, railroad industry for railcars and infrastructure, wind turbine construction, and automotive and aviation for structural components. Additionally, SAW is crucial in fabricating heavy equipment like pipes, boilers, and pressure vessels, and in the nuclear and energy sectors for contamination-free welds. It is also extensively applied in general industrial fabrication, including structures like rotary kilns and railway coach undercarriages.
Submerged Arc Welding (SAW) offers several advantages, including high-quality welds with excellent mechanical properties, high efficiency due to its high deposition rate, effectiveness for welding thick materials, and enhanced safety with minimal fumes and spatter. It also supports automation, ensuring consistent results and minimal cleanup with substantial flux recovery. However, its limitations include restrictions to ferrous materials, positional constraints, the need for flux handling and slag removal, poor arc stability at low currents, and challenges in directly observing the welding process, which necessitates automatic seam tracking devices.
Submerged arc welding (SAW) can be automated by employing mechanized systems that use a continuously fed electrode and automatic flux feeding to ensure consistent welding parameters. Robots can be utilized to manipulate the welding torch for continuous welding on complex parts, enhancing productivity and reducing defects. Automation allows for precise control over welding current, arc voltage, and travel speed, ensuring high-quality welds. Additionally, automated systems can incorporate various variants and use either AC or DC current to optimize the process for specific applications, further increasing efficiency and consistency in SAW operations.
When using submerged arc welding (SAW), several critical safety measures must be implemented to protect the operator and ensure a safe working environment. Operators should wear proper Personal Protective Equipment (PPE) such as welding gloves, safety glasses, a face shield, and heat-resistant clothing to prevent burns and exposure to UV radiation. Ensuring that welding equipment is properly grounded and avoiding work in wet or damp conditions is essential to prevent electrical shocks. The work environment should be free from flammable materials and obstructions. Proper handling and storage of flux to avoid inhalation risks, comprehensive training, and adherence to regulatory guidelines are also crucial for safety.
Flux recovery in submerged arc welding (SAW) is managed through specialized systems that efficiently collect and recycle unused flux. These systems typically consist of an aspirator and a hopper, which separate slag and fines from the clean, reusable flux. The recovered flux is then filtered to ensure it is free from contaminants and ready for reuse. This process enhances efficiency, reduces waste, and saves resources, contributing to economic savings, consistent weld quality, and improved productivity. Additionally, flux recovery units are designed for easy installation and operation, often being portable and maintenance-free for continuous use.
