What is meant by checking the "hi-low" of a flange?

Checking the "hi-low" of a flange refers to the process of visually inspecting the flange edges to ensure they are properly aligned with one another. This alignment is crucial for creating a good seal when the flanges are bolted together. Misalignment, which can result in a "high" or "low" point, can lead to leakage or failure of the joint, impacting the overall integrity of the system.

Proper flange alignment ensures that the surfaces are even and that there’s uniform contact along the mating surfaces. This is particularly important in systems where joint integrity is critical, such as in piping systems carrying fluids or gases under pressure.

The other options mentioned, such as measuring flange thickness or checking bolt tightness, are related to flange maintenance but do not specifically pertain to the concept of "hi-low." Adjusting the flange to match another part is more about modification rather than the alignment that "hi-low" checking focuses on. Thus, visually checking the flange edges for proper alignment is the correct action to ensure a sound mechanical connection.