The minimum inside radius of a bend in metallic pipe in a gas system is how many times the outside diameter of the pipe?

• A. 3x
• B. 4x
• C. 6x
• D. 8x

Answer: (C)

In metallic gas piping, bends must be made with a sufficiently gradual curve to prevent excessive stress on the pipe walls and to maintain a gas-tight joint. The minimum inside bend radius is six times the outside diameter of the pipe. This relatively large radius keeps the bend from becoming too sharp, which would concentrate stress on the inner wall, increase the risk of wall thinning, cracking, or failure at the bend, and make proper fitting or welding more difficult.

If the bend were tighter than this, the inner wall would experience higher tensile stress and potential damage over time, along with greater resistance to flow changes and possible gas leaks. A larger radius, while perfectly acceptable, isn’t required by the standard rule and would just produce a longer bend than necessary.