This glossary defines terms as they are used in this text. In some cases, the definitions may differ slightly from strict dictionary definitions.

A

Acute hazard.

A potential threat whose consequences occur immediately after initiation of an event. Examples include fire, explosion, and contact toxicity.

Anode.

A component of a corrosion cell, the anode is the metal that gives up ions and loses mass during the corrosion process. It is designed to sacrificially deteriorate in order to prevent the protected structure (the cathode) from corroding.

Anode bed.

Generally comprised of many individual anodes bars or packets of materials that are naturally anodic compared to steel. These individual anodes are electrically connected and installed together underground in a bed.

Anomaly.

An indication of potential pipe wall flaw or defect discovered during an in-line inspection. It is often not known if an anomaly is really a flaw until it is investigated.

Automatic valve (also called automatic block valve).

A mechanical device that prevents flow in a pipeline and is designed to operate when it receives a predetermined signal. The signal is transmitted without human action. See also Remotely operated valve .

B

Backfill.

The soil that is placed over a pipe as one of the final steps in pipeline installation. Sand is often used as a backfill material because of the uniform support it provides and because it does not damage the pipe coating during installation.

Block valves.

Block valves are designed primarily to function in either...