Consumables Corner: Why defects happen with one-sided submerged arc welding

Canadian Fabricating & Welding

Q: We are a structural steel shop that fabricates beams of various shapes and sizes. We often splice together plates for box beams or webs on I-beams by using a one-sided submerged arc welding process. Lately we have seen more weld issues such as lack of penetration or poor bead shape on the back-side weld. We recently changed our filler metal supplier and have a newer operator on the machine. Do you have any suggestions to fix this?

A: One-sided submerged arc welding (SAW-OSW) is a unique process that produces a high-quality weld deposit that appears to be welded from both sides while being welded only from the top side. This process has many variables that must be controlled very closely to produce repeatable, quality welds.

Let's start with the basic variables for SAW. Wire and flux, volts, amps, contact-tip-to-work distance (CTTWD), travel speed, torch travel angle, joint type and uniformity, and electrode spacing if you are using a tandem process can greatly affect weld performance and quality.

For OSW applications, additional variables include backing flux tray dimensions, joint gap consistency, type of backing flux (acidic, neutral, or basic), backing flux depth consistency, and plate clamping consistency (magnetic or mechanical).

The two issues you have experienced—lack of penetration and inconsistent backing weld appearance—are probably the two most common problems with SAW-OSW. Sometimes they can be resolved by adjusting one variable, but many times it requires an adjustment to a combination of several variables.

You stated that you changed filler metal supplier, and we’ll assume that means your flux manufacturer changed too. If so, make sure the wire, and more important the flux, is the same classification and type. In many OSW applications, two different fluxes are used, so make sure they are both correct for this process. Backing flux plays a huge role in backing weld consistency.

As with any weld manufacturing process, you should have proven welding procedure specifications (WPS). Double-check to make sure your operator is following the WPS and provide additional training so they understand what the variables are and how they affect weld performance and weld bead quality.

Whether you're welding with a single wire or a tandem configuration, the lead wire should be run on direct-current electrode-positive with constant-current arc control. This produces the best penetration of all polarities. Make sure CTTWD is correct and that the distance is roughly eight times the wire diameter and measured from the bottom of the weld joint.

Travel speed can affect penetration in two ways. First, weld penetration depends on heat input. High heat input should produce deeper penetration, but there is a limit, which leads us to the second factor. If travel speed is too slow, the weld puddle can advance in front of the welding arc, which acts like an insulator and reduces the arc's ability to penetrate deep into the joint.

Last, make sure the backing flux tray is in good condition and has the appropriate dimensions for the material thickness you are welding. The base material needs to have good contact with the top legs of the channel, which produces a dam that supports the backing flux. If the plates are not making good contact with the copper flux tray, the molten weld metal can eject out the side from the pressure. Also, be sure the backing flux is not disturbed while moving the plates into position for welding. These are all things that can affect back bead profile.