Page 406 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

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Glossaryl381

Glossary

This glossary defines terms as they are used in this text. In leaks. These have historically been used primarily where a
some cases, the definitions may differ slightly from strict dic- pipeline crosses under a road or railroad.
tionary definitions. Cathode. A component of a corrosion cell, the cathode is the
metal that attracts ions and gains mass through the corrosion
Acute hazard. A potential threat whose consequences occur process.
immediately after initiation of an event. Examples include Cathodic protection (CP). Method of protection against
fire, explosion, and contact toxicity. galvanic corrosion of a buried or submerged pipeline. In the
Anode. A component of a corrosion cell, the anode is the CP method, a low-voltage charge is impressed on a metal in
metal that gives up ions and loses mass during the corrosion order to protect it from corrosion. Essentially, the pipeline is
process. It is designed to sacrificially deteriorate in order to turned into a cathode by application of protective currents,
prevent the protected structure (the cathode) from corroding. which prevents the loss of metal. The CP system is generally
Anode bed. Generally comprised of many individual comprised of anodes, rectifiers (when needed), electrical
anodes-bars or packets of materials that are naturally connections, and monitoring points.
anodic compared to steel. These individual anodes are Chronic hazard. A potential threat that can continue to
electrically connected and installed together underground in cause harm long after the initial event. Examples include car-
a “bed.” cinogenicity, groundwater contamination, and long-term
Anomaly. An indication of potential pipe wall flaw or defect health effects.
discovered during an in-line inspection. It is often not known Check valve. A special type of valve or flow-restricting
ifan anomaly is really a flaw until it is investigated. device designed to allow flow in one direction only and pre-
Automatic valve (also called automatic block valve). A vent flow in the other.
mechanical device that prevents flow in a pipeline and is Cleaning pigs. A device transported through the pipeline to
designed to operate when it receives a predetermined signal. remove scale and sediment.
The signal is transmitted without human action. See also Close interval survey. In this technique, pipe-to-soil voltage
Remotely operated valve. measurements are performed every 2 to 15 feet along an
entire pipeline to test if CP levels are adequate. Ideally, such
Backfill. The soil that is placed over a pipe as one ofthe final a profile of pipe-to-soil potential readings will indicate areas
steps in pipeline installation. Sand is often used as a backfill of interference with other pipelines or casings, areas of inad-
material because of the uniform support it provides and equate CP, and even areas where pipe coating is defective.
because it does not damage the pipe coating during installa- Coating. A material that is placed around and adheres to a
tion. pipeline component to protect that component from contact
Block valves. Block valves are designed primarily to func- with a potentially harmful substance.
tion in either the fully closed or fully opened position. They Control valves. These valves are designed to operate in the
are used to stop flow completely, rather than throttling or full range of positions from closed to fully open. The func-
controlling the flow rate. Block valves can be closed auto- tion of control valves is to control fluid flow rates by operat-
matically, remotely, or manually depending on the closure ing in partially open positions.
mechanism. Block valve designs include gate-, plug-, and Corrosion. The wearing away of a material, usually by a
ball-type configurations. chemical reaction.
Casing. A pipe completely surrounding the pipeline to pro- DOT. Department of Transportation. The regulatory agency
vide protection and act as a conduit for potential product of the U.S. government that is charged with regulating