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What is Electroslag Welding? (Definition, Pros and Cons)


What is Electroslag Welding?

Electroslag welding (ESW) is a single pass welding process for joining thick materials in a vertical or near-vertical position. This highly productive welding technique uses a filler metal and the heat generated between two materials from an arc and electrical resistance.

The heat generated by the electric arc initially melts the filler metal as well as the surfaces of the metals to be joined. The arc is then extinguished and the molten slag, which is conductive, provides heat to melt the filler metal and base metal, as well as protection from atmospheric contamination as it travels along the weld joint.


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How Does Electroslag Welding Work?

The electroslag welding process starts by creating an arc between a consumable electrode and the workpieces. 

This arc melts the filler metal to create a conductive molten slag, which moves along the weld joint, offering protection against atmospheric contamination as well as heat, to ensure complete fusion between the two pieces being joined. Once the weld is complete, any excess slag can be removed from the finished weld joint.

The electroslag welding principle is similar to submerged arc welding, except that the latter uses an electric arc to provide heat and non-conductive slag to provide protection, whereas for the first, an electric arc is only used to start the process, then both heat (resistance heating) and protection are provided by the molten slag, which is conductive.

Advantages of Electroslag Welding

Electroslag welding offers a number of advantages over other welding processes, including:

  • Speed: The primary advantage of electroslag welding is the high deposition rates in comparison to other processes - the process can be made semi-automatic, which can further reduce the welding times
  • Penetration: This welding technique offers excellent penetration into thick materials, making it perfect for heavier industrial applications such as shipbuilding
  • Minimal Preparation: Another factor that speeds up the process as well as reducing costs is the minimal requirement for joint preparation before welding
  • Fewer Defects: The uniform bead profile and lack of cracking and porosity means there are fewer defects than with other processes

Disadvantages of Electroslag Welding

Although electroslag welding offers plenty of advantages, there are drawbacks too:

  • Grain Structure: The coarse grain structure produced by ESW can lead to a lower toughness
  • Positioning: Since ESW is only done in a vertical or near-vertical position it may not be suitable for some applications
  • Material Thickness: ESW is not suitable for joining thinner materials
  • Cooling: The high temperatures associated with ESW may require additional cooling arrangements to ensure high quality welds
  • Set-Up Costs: While ESW is an inexpensive welding process in itself, the initial set-up costs for an electroslag welding station are typically higher than for other more traditional processes

Tools and Materials

Electroslag welding uses a range of materials alongside the base metal and any filler metals. These include flux, a consumable wire guide, retaining blocks, and more. Here is an overview of these materials:

  • Filler Metal: The filler metal melts at the weld join and helps join the workpieces together
  • Flux: This turns electrical energy into heat to help create the molten slag
  • Power Source: This provides the electrical current that creates heat for the weld
  • Retaining Blocks: Holds the workpieces in place during welding
  • Welding Head: Assists with the control and travel direction of the molten slag
  • Wire Feeder: Feeds the filler metal into the weld pool
  • Wide Guide: A consumable guide tube can be used to protect the electrode from being consumed by the slag as it is guided into the weld pool

Applications of Electroslag Welding

Due to the high deposition rate and excellent rates of penetration into thick materials, electroslag welding and has historically being used to manufacture large civil structures and in shipbuilding.


Electroslag welding is an efficient and effective process for joining thick materials in a vertical or near-vertical position. Often used in heavier industries such as shipbuilding and construction, this process produces a uniform bead profile with little porosity or cracking, meaning fewer defects than with other processes.

Despite the benefits, there are still drawbacks with this technique, including lower toughness as a result of the coarse grain structure that can be produced in the weld as well as high initial set-up costs.

However, with the careful consideration of machine and equipment selection, applications and safety features, electroslag welding can be used effectively for various tasks ranging from pressure vessel fabrication through to shipbuilding and heavy equipment manufacture.


Is Electroslag Welding a Fusion Welding Technique?

Yes, electroslag welding is a fusion process, using an electrical current and a conductive molten slag to generate resistance heating and join metal workpieces together. Used for thick materials, this technique creates strong, continuous welds that are durable and corrosion resistant.

Are there any Safety Considerations for Electroslag Welding?

It is important to follow the correct safety precautions and requirements when undertaking electroslag welding. Safety protocols include ensuring the working area is clear of flammable materials, as well as wearing eye protection and flame-resistant clothing. All safety equipment and tools should be checked before use and a fume extraction system should also be used to remove any hazardous fumes during welding.

How is Electroslag Welding Different from other Welding Processes?

Electroslag welding differs from other techniques as it uses an electrical current and a conductive molten slag to generate resistance heating and join metal workpieces together, whereas in the most common welding processes, the heat is generated by an electric arc (hence the term ‘arc welding’). It can weld thicker pieces more effectively than some other methods, creating durable and corrosion resistant welds and making it ideal for larger welding projects.

Difference Between Electroslag And Electrogas Welding?

The primary difference between electroslag and electrogas welding is that electroslag welding uses a conductive molten slag and heat is produced by resistance, whereas electrogas welding uses an electric arc to produce heat. Electroslag welding also produces a coarser grain structure and subsequently can lead to lower toughness than with electrogas welding. Electrogas welding also produces a cleaner weld and can be used on thinner materials than possible with electroslag welding. Each process has its own advantages and disadvantages that should be considered in alignment with your job requirements.

Is Electroslag Welding Suitable for Thin Materials?

Electroslag welding is not suitable for joining thin materials. Although it is a highly productive process, it uses a high level of heat and pressure, making it more suited for joining thicker materials. Thinner materials are better joined with other methods, such as MIG or TIG welding.

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