The inside radius of a bend in a fuel gas metallic piping system must not be less than what multiple of the outside diameter of the pipe?

In a fuel gas metallic piping system, the bend radius is crucial for ensuring smooth flow and minimizing stress on the pipe, which can cause leaks or failures. The requirement that the inside radius of a bend must not be less than six times the outside diameter of the pipe is based on industry standards and practices designed to maintain the integrity of the piping system.

When the inside radius is sufficiently large, it reduces the potential for internal pressure drop and turbulence that can lead to inefficiencies or hazards. A sharper bend could cause the walls of the pipe to undergo excessive stress and strain, potentially leading to deformation or breakage. Adhering to the six-times multiple helps to ensure that the flow remains practical and that safety is maintained throughout the operation of the gas system.

Other multiples, such as three, four, or five times the outside diameter, do not provide the same level of assurance regarding the stress distribution and flow characteristics within the piping, which is why they are less appropriate standards for metallic piping bends in gas systems.