This specification covers requirements and test methods for material dimensions and tolerances, hydrostatic burst strength, chemical resistance, and impact resistance of PEX pipe and tubing for use in fuel gas mains and services for direct burial applications. Requirements cover workmanship, pipe and tubing dimensions and tolerances, chemical resistance, sustained pressure, elevated temperature, thermal stability, slow crack growth resistance, minimum hydrostatic burst pressure/apparent tensile strength (quick burst), apparent tensile strength at yield, squeeze-off, thermal stability, slow crack growth resistance, and joints.