Adhesion Loss on Weldments

The problem we are having is around the orifices where there are a double set of welds. Our material, which adheres to most ferrous and nonferrous metals, is adhering to the vertical surfaces of the orifices with no problem. Shortly after application, however, it will flow off the welds, forming an area of foam around the bottom of the weld. We not sure why this is happening or what to do to correct it.

Q. Our paint company manufactures a line of zero-VOC waterborne DTM aliphatic urethanes. We have a customer producing carbon steel storage tanks who would like to switch to our material because he could use one less coat, and our material provides a better aesthetic finish and is environmentally friendly. The problem we are having is around the orifices where there are a double set of welds. Our material, which adheres to most ferrous and nonferrous metals, is adhering to the vertical surfaces of the orifices with no problem.

Shortly after application, however, it will flow off the welds, forming an area of foam around the bottom of the weld. We not sure why this is happening or what to do to correct it. I have attached the tech data sheet of the product for your review. We are spraying the material between 6–8 mils WFT.

Any help you can provide would be appreciated. B.D.

A. That sure is a great looking coating according to the tech data sheet! I’m not publishing it here due to space limitations.
The simple answer to the problem is rooted in physics and chemistry. Since your coating adheres to almost every metal, I can’t imagine that the problem is metallurgy owing to some change in the metal itself in the weldment area. The complicated answer is: Because of physics, the coating beads in the weldment area due to the presence of welding residue, which inhibits wetting of the surface. The coating foams in the weldment area because something in the coating formulation is reacting with the welding residue.

Since data sheets do not provide the chemical nature of paint formulations and I don’t know the composition of the welds, I can’t comment on the specific chemical reaction. To further complicate matters, these two phenomena could be inter-related. It looks like there is a problem with metal pretreatment. To solve the problem, your customer must remove the residue from the welding operation.