Pipe may be bent by any hot or cold method and to any radius that will result in a bend surface free of cracks, as determined by a method of inspection specified in the design, and substantially free of buckles. Such bends must meet the design requirements of 102.4.5 and 104.2.1 of ASME B31.1 (incorporated by reference; see § 56.01-2). This does not prohibit the use of bends designed as creased or corrugated. If doubt exists as to the wall thickness being adequate, Class I piping having diameters exceeding 4 inches must be nondestructively examined by the use of ultrasonics or other acceptable method. The nondestructive method must be employed where the design temperature exceeds 750 °F.