49 CFR §192.315

1. (a)A wrinkle bend may not be made on steel pipe to be operated at a pressure that produces a hoop stress of 30 percent, or more, of SMYS.
2. (b)Each wrinkle bend on steel pipe must comply with the following:
   1. (1)The bend must not have any sharp kinks.
   2. (2)When measured along the crotch of the bend, the wrinkles must be a distance of at least one pipe diameter.
   3. (3)On pipe 16 inches (406 millimeters) or larger in diameter, the bend may not have a deflection of more than 1 1/2° for each wrinkle.
   4. (4)On pipe containing a longitudinal weld the longitudinal seam must be as near as practicable to the neutral axis of the bend.