Tip #06 · Brownfield
The as-built drawing is a hypothesis, not a fact.
When identifying pipe on a brownfield site, measure the OD with a pi tape (a flexible tape that reads diameter directly), then use a UT thickness gauge for the wall thickness. You cannot measure wall thickness with a caliper on an installed closed pipe.
Treat every dimension on an existing drawing as unverified until you have personally checked it. The older the plant, the higher the probability that reality and documentation have diverged.
The UT gauge
The UT gauge sends a sound pulse through the wall and measures the echo time. This is how experienced field engineers identify pipe. Do not guess. Do not assume. Measure.
The takeaway: Budget one hour of field verification for every four hours of brownfield routing work. It is not extra time — it is the time that prevents rework. Document what you find and pass discrepancies to the document controller.
