What is the minimum bend radius of a bend for pipe sizes 2 1/2 in. and larger?

• A. Three pipe diameters
• B. Five pipe diameters
• C. Seven pipe diameters
• D. Ten pipe diameters

Answer: (B)

Bend radius is about keeping curves gentle enough so water can move smoothly and the pipe won’t suffer from kinks or excessive thrust. For standpipe and hose systems, NFPA 14 specifies that when you bend pipes that are 2-1/2 inches in diameter or larger, the bend radius must be five times the pipe diameter. That means, for example, a 2-1/2 inch pipe needs a radius of 12.5 inches; a 3 inch pipe needs 15 inches, and so on. Using this generous bend helps reduce friction losses and turbulence at the bend, reduces the risk of deforming the pipe or damaging fittings when the system is pressurized, and minimizes directional changes that could hinder hose deployment or flow.

Less generous bends would be too tight for these sizes and can create sharp flow changes, higher loss, and stress at the bend. More generous bends would be unnecessarily bulky and harder to fit in confined spaces while not providing meaningful extra benefit in typical standpipe installations. Five diameters is the practical standard that balances safety, performance, and installability.