Pipe thickness gauge vs my old calipers, night and day on site

Used to eyeball wall thickness with my calipers on boiler tubes near Baton Rouge, always second guessing myself. Last month my buddy let me borrow his ultrasonic gauge and I measured a 1/2 inch line that was actually down to 0.35, corrosion hiding behind the paint. Now I check every suspect spot on tubes before we even talk about welding a patch. Anyone else run into hidden thinning that looked fine from the outside?

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wyatta302h ago

Wait, so you were getting readings that far off with calipers on painted surfaces? That's exactly why I stopped trusting mine for anything thicker than sheet metal. The paint layer alone can throw you off by 20 to 30 thousandths, and if there's any scale or pitting underneath, forget it. Once I switched to the ultrasonic method I found a similar spot on a discharge line that looked perfect on the outside but had lost half its wall from internal erosion. The problem is you can't see that kind of damage coming, it just shows up one day when you're doing a hydro test and suddenly you've got a leak. I make it a habit now to check every elbow and weld zone on old lines before we even break out the torch, because that hidden thinning is what actually gets people hurt.