If tap holes must be drilled into the pipe (or flanges) at the process site, great care must be
taken to properly drill and de-burr the holes. A pressure-sensing tap hole should be flush with the
inner pipe wall, with no rough edges or burrs to create turbulence. Also, there should be no reliefs
or countersinking near the hole on the inside of the pipe. Even small irregularities at the tap holes
may generate surprisingly large flow-measurement errors