"CS/SS U-tube bundle corrosion"
"We have a U-tube HEx (heater) with steam service on the shell side, hot (350 deg F) product on the tube side. The tube bundle has SS tubes with a CS tubesheet. This was installed after the old CS tubes were failing (but the CS tubesheet looked okay). Now we have noticed corrosion on the tube sheet and surface around the weld areas is eroding/corroding such that the weld edges are intact but exposed (and sharp). So it looks like the tube sheet is taking the brunt of the corrosion and the SS tubes are fine. I am looking for alternatives to purchasing a new totally bundle (coatings, etc.). If a new bundle is considered the most reliable way to go, what materials should I consider (will all SS hold up to cracking and such)?"
From your description, it appears that the carbon steel tubesheet is experiencing galvanic corrosion from contact with the SS tubes. You might try overlaying the existing tubesheet with SS.
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