A freeze in time

This article discusses the use of freeze plugs in the maintenance of industrial plants. In 2006, ASME published a standard PCC-2—Repair of Pressure Equipment and Piping—to guide plant personnel in the swift and safe execution of several lesser-known but very valuable repair techniques, regardless of their experience. One such repair technique that is well documented in PCC-2 is the use of freeze plugs, which prevent flow in pipes to allow for downstream maintenance activity. A freeze plug, unlike the hot tap, does not compromise the integrity of the pipe pressure boundary by welding or drilling. The freeze plug is created by installing a bolt-on jacket around the pipe through which liquid nitrogen (at –321°F) is circulated until the water in the line freezes. Employing a freeze plug can prove to be more efficient both in terms of cost and schedule than the other repair alternatives. The concept is simple but execution must be well planned.