Use of cryogenic and low-temperature pressure vessels is increasing rapidly, but there have been many defects caused by improper materials and poorly designed vessels, particularly those meant for low-temperature service. Many materials exposed to low temperatures lose their toughness and ductility. As the temperature goes down, the metal has a tendency to become brittle. This may cause brittle fracture at full stress.

Most materials used for service at normal temperatures have a marked decrease in impact resistance as temperatures decrease. These materials must have the proven ability to safely resist high-stress changes and shock loads. Only impact-tested materials able to withstand unavoidable stress concentrations should be used for cryogenic vessels. All sharp or abrupt transitions or changes of sections, corners, or notches should be eliminated in the design of the vessel and fabrication of its parts.

Manufacturers, purchasers, and users of low-temperature pressure vessels often misunderstand certain paragraphs in the ASME Pressure Vessel Code. Perhaps it might be helpful to clarify various paragraphs applying to low-temperature vessels and to indicate when impact tests are required. If such tests are necessary, each part of the vessel must be considered: shells, heads, nozzles, and reinforcing pads, as well as other pressure parts. Additionally, nonpressure parts welded to pressure parts shall also be considered. Therefore, to impact-test or not can be a large cost factor.

The 1987 Addenda of the ASME Boiler and Pressure Vessel Code, Section VIII, Division 1 mandated new toughness requirements and specified...