Why does nobody mention 1/4 inch plate buildup on older tanks

I was going through some old job files from the late 90s last week and found out a tank I worked on back then had almost 3/8 inches of scale and rust built up on the inside. The original spec said 1/4 inch plate but after sandblasting we were down to 3/16 in some spots. It surprised me because we never caught it on the initial inspection. Has anyone else run into hidden thickness loss like that on older vessels?

2 comments

2 Comments

finleybutler4d ago

Read somewhere that internal buildup hides corrosion until you blast it.

janahenderson4d ago

Huh, is that actually true though? I mean, I've seen it happen with old farm equipment we dug up from a field, where the dirt and grime just held everything together until we hit it with a pressure washer. But in my experience, corrosion usually finds a way to bubble up or flake through the paint long before you blast it, unless the buildup is really thick and greasy like inside an engine block. Your mileage may vary depending on the metal and how long it's been sitting, though. Take this with a grain of salt, but I'd say you're right to be suspicious of anything that looks clean but has years of gunk hiding underneath.