AWWA C150

Applies to: Structural thickness design of ductile-iron water and wastewater pressure pipe; accounts for internal pressure, external soil load, and live loads; pipe pressure classes 50–56; standard laying conditions A–E.

Does NOT cover: Plastic pipe (AWWA C900/C906 for PVC/PE); steel water pipe (AWWA C200); in-plant ductile-iron piping not in buried service; thrust restraint design (AWWA M41 manual applies).

• Design earth cover depth and live load selection (AASHTO H-20 or H-25 truck loading)
• Working pressure input including surge allowance (100 psi above normal operating pressure)
• Laying condition selection (Types 1–5 per soil support quality)
• Minimum wall thickness calculation per pressure class formula
• Pressure class selection from tables (Class 50–56 based on combined loading)
• Corrosion allowance for aggressive soils (polyethylene encasement per AWWA C105)

AWWA C150 is the design standard used to select ductile-iron pipe pressure class for water main projects. Its trench-loading model accounts for both internal pressure surge and the external earth/live load combination. The standard incorporates a 100 psi surge allowance above the working pressure, meaning pressure Class 50 pipe (minimum of 150 psi) is adequate for a 50 psi working pressure system after surge.

Engineering note: In deep-trench or heavy-traffic installations, the external earth load can govern the pressure class selection rather than internal pressure. Always calculate both the pressure-based class and the earth/live-load class and select the more conservative result. For aggressive soils (low resistivity, sulfide-containing), specify polyethylene encasement (AWWA C105) in addition to the calculated pressure class to protect against external corrosion.