In a metal tubing installation, which statement is true?

• A. rigid straight line runs are preferable
• B. tension is undesirable because pressurization will cause it to expand and shift
• C. a tube may be pulled in line if the nut will start on the threaded coupling
• D. none of the above

Answer: (B)

When metal tubing is used under pressure, avoiding tension in the run is important. Inside pressure tends to elongate the tube slightly, and if the tube is already under tension, that extra elongation can push on fittings and joints, causing movement, misalignment, or leaks. So the idea that tension is undesirable because pressurization will cause the tube to expand and shift is the best guiding principle: provide enough allowance for expansion and movement, use proper supports, and avoid pulling the tube tight.

Rigid straight-line runs aren’t inherently preferable because they don’t always accommodate thermal expansion or small movements at joints, which can lead to stress or leaks. Starting the nut on a threaded coupling to pull the tube into line is a misalignment risk that can damage threads or create leaks, so that practice isn’t advisable.