Copper tubes and fittings are widely used in the industrial gas industry because of their outstanding cryogenic properties, high toughness, and easy installation. However, one notable disadvantage of the copper materials is their low allowable stresses and hence low-pressure rating in the annealed condition. ASME B31 Code Case 216 has been developed to overcome this shortcoming. The Code Case provides detailed design and construction procedures for copper tubes and fittings and permits significantly enhanced pressure rating with no compromise in B31.3 design safety factor. This paper documents the technical details of the Code Case development. By taking advantage of excellent work hardening and toughness properties, especially at cryogenic temperatures, it was demonstrated that a significant increase in allowable stress can be obtained for copper tubes after a small amount of cold work. The work hardening is achieved by a carefully controlled cold stretch operation simultaneously done during the pressure test. Through extensive destructive testing, it was shown that the pressure rating of the copper tubes and fittings can be safely increased more than 60% compared with traditional B31.3 designs. Additional limitations and safety precautions are also discussed when applying this Code Case.