Inspectioneering Journal

99 Diseases of Pressure Equipment: Inadequate Overlay Weld Thickness and Chemistry

This article appears in the January/February 2004 issue of Inspectioneering Journal.

When we specify that some equipment (vessels, flanges, fittings, etc.) be overlaid with a corrosion resistant alloy, we need to pay attention to making sure that the chemistry of the top layer of alloy welding, that will be exposed directly to the process fluid, is sufficient to resist degradation from the process environment. This may sound logical, but I’m aware of several cases where weld overlaid surfaces are ground or machined to meet specification tolerances, and in so doing the most resistant part of the alloy overlay is removed. This is especially true on flanges or other bolted- gasketed surfaces where dimensional issues and surface quality are more important. So if you anticipate removing some weld overlay alloy, you need to design your fabrication process so that you will still have sufficient chemistry in your eventual top surface to meet alloy specifications. Don’t imagine that the machinist will know that he is defeating part of your specification by meeting your other requirements.

Have you ever seen localized corrosion or rust stains bleeding through a weld overlaid surface and wondered what the problem was?

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