Tubing is sized based upon the inner diameter, unlike piping.

Tubing is sized based upon the inner diameter, unlike piping.

• A. True
• B. False
• C. Not enough information
• D. Both are true

Answer: (B)

Tubing is sized by its outside diameter because that dimension determines which fittings and connections it uses. The inner bore is then a result of the tube’s wall thickness, so different wall thicknesses can give the same outer diameter but different internal bore. In contrast, piping is sized by nominal pipe size, which is tied to an approximate inside diameter for a given wall thickness (schedule). The actual inside diameter changes with the wall thickness, so the sizing basis for piping isn’t the bore itself. Therefore, the statement that tubing is sized based on the inner diameter is not correct.

Tubing is sized by its outside diameter because that dimension determines which fittings and connections it uses. The inner bore is then a result of the tube’s wall thickness, so different wall thicknesses can give the same outer diameter but different internal bore. In contrast, piping is sized by nominal pipe size, which is tied to an approximate inside diameter for a given wall thickness (schedule). The actual inside diameter changes with the wall thickness, so the sizing basis for piping isn’t the bore itself. Therefore, the statement that tubing is sized based on the inner diameter is not correct.