Fundamentals of Electrogas Welding

Electrogas welding is an arc welding process that uses an arc between a continuous filler metal electrode and the weld pool. Continue reading this article to learn much more, including advantages and limitations.

AWS Publications | August 26, 2021 | Processes
Welding Digest ►  Fundamentals of Electrogas Welding

Electrogas welding is an arc welding process that uses an arc between a continuous filler metal electrode and the weld pool. Continue reading this article to learn much more, including advantages and limitations.

It employs an approximately vertical welding progression with a metallic or nonmetallic backing to confine the molten weld metal. The backing is a dam-like device that is placed against the back side of the weld joint or on both sides of the weld joint to support and retain the molten weld metal. Depending on the type of backing used, it may be fused to the weld joint and become part of the weld or remain unfused and removed after welding. The process is used with or without an externally supplied shielding gas and without the application of pressure. The electrode for electrogas welding is usually in the form of a solid or cored wire and is often used with a consumable guide tube.

Typically, in electrogas welding, a square-groove or single-V-groove joint is specified and positioned with the axis or length of the weld vertical. No repositioning of the joint occurs once welding has started; welding continues to completion so that the weld is made in one pass.

The consumable electrode (either solid or flux cored) is fed downward into the joint root opening, which is a cavity formed by the base metals to be welded and the backing shoes. A starting weld tab (sump) is required to seal the bottom of the weld joint to allow the process to stabilize and to support the molten weld metal until it reaches the workpiece. An arc is initiated between the electrode, consumable guide tube (when one is used), and starting weld tab. The heat generated by the arc melts the continuously fed electrode and groove faces. Melted filler metal and base metal collect in a pool beneath the arc and solidify to form the weld. As the weld metal fills the joint, the weld pool rises, progressing in the uphill direction.

Thicknesses of 13 mm (1⁄2 in.) to 38 mm (1 1⁄2 in.) are typically welded with electrogas welding. When thicker sections are welded, the electrode may be oscillated horizontally through the joint for uniform distribution of the heat and weld metal. If moving shoes are used, one or both shoes may move upward as the cavity fills. Although the weld travel is vertical, the weld metal is actually deposited in the flat position at the bottom of the cavity.

Electrogas welding is a mechanized welding process. The nature of the melting and solidification during welding results in a high-quality weld deposit. Little or no angular distortion of the base metal occurs with single-pass welds. For these reasons, major applications of electrogas welding have historically been in tank fabrication and shipbuilding.

1 electrogas welding-1Electrogas welding of a ship hull using two machines controlled by one operator.

 

Advantages and Limitations

Several of the advantages associated with electrogas welding, such as high deposition rates and operating factors, have resulted in considerable cost savings, particularly when welding thicker metals. Savings have been achieved for applications in which components can be joined in the vertical position with a continuous vertical weld. For thicker materials, electrogas welding is often less expensive than the more conventional joining methods, such as submerged arc and flux cored arc welding. Even in some applications involving thinner base materials, electrogas welding may result in cost savings because of its efficiency and simple requirements for joint preparation.

However, the electrogas welding process has several limitations, including the following:

 

1. The training of operators is time consuming and critical to the successful use of the process;

2. The initial cost of equipment is high and set up time can be lengthy;

3. The high heat input may cause lower toughness in the weld and heat-affected zone, as measured by Charpy tests; and

4. If the weld is not completed in one continuous pass, the resulting restarts usually require that a repair be made. Additionally, the reworking of problem welds is difficult.

5. Electrogas welding is not generally used for applications involving aluminum alloys and stainless steel, although a few successful examples have been reported.

 

This article was excerpted from the Welding Handbook, Ninth Edition, Volume 2, Welding Processes, Part 1.