Aug 26, 2023
Consumables Corner: Troubleshooting lack of fusion and porosity in submerged arc welding applications
Phynart Studio / E+ / Getty Images We fabricate various products such as tanks and pressure vessels. At times we struggle with lack of fusion (LOF) and porosity near the middle of the weld joint on
Phynart Studio / E+ / Getty Images
We fabricate various products such as tanks and pressure vessels. At times we struggle with lack of fusion (LOF) and porosity near the middle of the weld joint on complete joint penetration welds. The porosity appears as small to large gas pockets near the weld centerline. Any ideas on what may be causing these problems and how to resolve them?
This is a common issue with submerged arc welding (SAW) when complete joint penetration is required. In most cases, this happens when the application is designed to be welded from both sides. This is much less of an issue in applications where the joint is welded from one side only.
In many applications, the components to be welded together will have a root weld performed with gas metal arc welding, flux-cored arc welding, or even shielded metal arc welding. This operation holds the components together until they can be welded completely with SAW. It also serves the purpose of providing a base for the SAW process to prevent burn-through.
The joint design for two-sided welds is either equal double V-groove; offset double V-groove, where one side has a larger groove; or single V-groove. It also may be an equal or offset double bevel, otherwise known as a K bevel. This is usually done to accommodate easier access to the weld joint, such as on a tank or vessel. The joints range from knife edge preparation up to a 6-mm root face or land, which helps reduce the required amount of filler metal and weld time.
LOF is the result of inadequate weld parameters, inconsistency in the weld joint, and/or improper weld head setup (which typically occurs on circumferential welds).
To resolve LOF, developing robust welding parameters is the obvious first step. Having a consistent weld joint may not seem like a big concern; however, wide variation in the root face thickness or root gap can result in LOF if the root face is too large or the gap is too tight or burn-through if the root face is too small or the gap is too wide. Holding joint dimensions to tight tolerances is essential in achieving consistent weld quality.
On circumferential welds, offsetting the weld head at the proper distance from top or bottom dead center is critical to weld quality. The details of proper weld head offset are more than can be covered here, but it should be included in the training for the SAW operator who will make circumferential welds.
Centerline porosity on the second side welded is common in areas where there is LOF, so solving this issue will also solve porosity in most cases.
Porosity also is caused by joint contamination, absorbed moisture in the flux, or welding over a root pass weld that contained porosity.
Porosity usually can be eliminated by preheating and by ensuring that the weld joint is clean, the flux is dry and from new or unopened bags or reconditioned in an oven, and the root weld pass is free of porosity.
Often, SAW operators are not experienced manual welders and do not have the same knowledge base as their counterparts. Additionally, due to the arc and weld puddle being covered, it is difficult to grasp the concepts of the process. Therefore, experienced and inexperienced SAW operators should be provided with classroom training to better understand the variables and how they can be utilized to troubleshoot related weld quality issues.