How to Protect Against Selective Seam Weld Corrosion
Selective seam weld corrosion (SSWC) is a type of environmentally-assisted corrosion affecting the bond-line region and heat-affected zone (HAZ) of longitudinal welds. It preferentially attacks the weld zone rather than the base metal. This is particularly prevalent in pipelines made with electric resistance welded (ERW) seams, and with galvanized steel tubes.
The problem is particularly troubling with galvanized steel tubes. Welding of galvanized stainless steel can cause zinc depletion due to its lower boiling point compared with the base metal. This causes zinc to volatilize at and adjacent to the weld joint, effectively eliminating the benefits of galvanization.
Zinc depletion can cause localized corrosion attacks along the weld line, which can lead to premature component failure. Naturally, preventing this phenomenon is a priority in industries where the integrity and longevity of weld structures are critical. Pipeline safety regulations in the US have established minimum integrity management requirements, including selective seam weld corrosion guidelines. So, what are the strategies for preventing SSWC and ensuring the long-term durability of welded joints?
How Zinc Metalization Can Help
Zinc, or zinc-aluminum, metalization can provide a reliable measure of corrosion control, offering a long-lasting coating solution for galvanized steel tubes. Metalization involves thermal spraying a thin layer of metal onto a substrate. The molten feedstock mechanically bonds to the surface, creating a thin metallic film over the welded seam area. This restores the benefits of galvanization to the welded seam. Zinc-metalized stainless steel tubes are far more effective at withstanding SSWC.
Metalization via flame spraying is a highly advantageous solution for protecting against SSWC. It enables an even coating that is finely adjustable based on wire diameter and flame spray parameters. Arc spraying is used as an alternative. However, arc spray typically offers efficiencies of up to 65% while flame spraying can reach 85%. This makes flame spray metalization a highly economical solution.
Looking for Help with Weld Seam Corrosion?
At Saint-Gobain, we offer a range of user-friendly flame spray systems suitable for zinc metalization. It can be readily used on the tube line, enabling high ease of installation. The Top-Jet and Z-Jet Flame Spray Guns’ compact and versatile configuration enables users to readily deposit various coating types on-site. Flame spraying is also safer than arc spraying, producing minimal zinc emissions, thus prioritising worker safety. We also offer fully automated solutions like the Master Jet Auto IV Flame Spray System, which was designed with robotization in-mind. It is the optimal solution for high-throughput metalization applications.
Our flame spray systems are highly compatible with zinc, aluminum or zinc-aluminum wires, offering flexibility in coating applications.
We also offer metallic wires in Europe and proprietary Flexicords and Rokide® rods for optimal high-performance coatings worldwide.
If you want to learn more about the benefits of metalizing seam welds or coating solutions for weld seam protection, why not contact a member of the Saint-Gobain team today?