Sentry holes

On older process units, you may still encounter piping with sentry holes. Let s say I have a Vfc-in thick pipe. The corrosion allowance for the pipe is Vi in. A number of small holes are drilled into the pipe, to a depth of in. When we start leaking at these small holes, this means that the pipe has corroded to its discard thickness in the area of the sentry hole. Incidentally, you can stop the resulting leak, at least in carbon steel water lines, with a brass wood screw and a screwdriver. I have also done this on hydrocarbon lines under an 80 psig pressure, but perhaps that is not too smart. 

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