Faced with rising operating costs due to increasing energy and chemical prices as well as stricter effluent permit limits, many operators and...
Protecting pipeline to secure water supply
Corroded pipeline leads to an estimated 1.7 trillion gal of water leaks per year. WWD Assistant Editor Amy McIntosh spoke with Richard Grant, principal at Russell Corrosion Consultants, about the origin of corrosion and the importance of treatment.
Amy McIntosh: How does corrosion originate in a water pipeline?
Richard Grant: Corrosion is a naturally occurring electrochemical process in nature. Corrosion is nature’s method whereby metals and alloys return to their unrefined, naturally occurring forms as elements and minerals. When ore is refined, this natural and most stable state is reversed to produce the actual metal, which is less stable under natural conditions than the base element. A large amount of energy is applied to the base metal as the metal is converted from its oxide, carbonate, sulfide, etc. Given the right conditions, these high-energy and more ordered metals tend to revert to their low-energy state and less ordered elemental condition.
Thus, with most metals, including iron and steel alloys, this means that, under most natural conditions, unless special precautions are followed, metals will combine with oxygen to form rust and corrosion.
Virtually all forms of corrosion occur by the same basic electrochemical reaction as oxidation. As the name of the reaction implies, the presence of oxygen or oxidizers is not only required for the reaction to begin, but to continue. Essentially, the metal combines with oxygen to form an oxide substance, which manifests itself as rust or corrosion.
McIntosh: Once corrosion exists, how can it be treated?
Grant: The most important fact is that this electrochemical process can be stopped or slowed to a manageable rate through the application of various corrosion prevention measures. Treatment methods for corrosion of pipeline can include protective coatings or cathodic protection.
Protective coatings can be utilized effectively as the “first line of defense” for pipeline protection. Extruded polyethylene, fusion-bonded epoxy and polyurethane coatings can all be utilized in different applications on different substrates. These coatings work by dielectrically isolating the pipe from its surrounding environment and thus preventing the oxygen and other components necessary for the corrosion process to propagate.
There are several ways to deter the corrosion of iron, one of which is cathodic protection. This method is used on submerged marine structures, water storage tanks, underground gas pipe, oil platform supports and other structures exposed to corrosive surroundings. Cathodic protection works by eliminating anodic (corroding) areas and rendering the structure to be protected a complete cathode. This works by utilizing an external anode, which flows current through the soil onto the pipe surface. Anodes consume themselves over time and must be replaced periodically.
McIntosh: What are the short- and long-term effects of corrosion in water pipeline?
Grant: Our nation’s water and wastewater infrastructure is already in a deteriorated state. Corrosion is literally eating away at our nation’s water and wastewater pipeline every day. The short-term effects are more pipeline failures, loss of revenue for the water utilities, loss of service for the consumer and potential hazards when lines fail (flooding, discharge of unsafe water into environmentally protected areas, loss of homes, etc.). In addition, the cost to replace this infrastructure is enormous and growing by the year.
Longer term—unless we begin to take a proactive stance on protecting our water and wastewater assets—there is a replacement budget that we will not be able to pay for and a loss of precious water that we cannot replace. Utilities and owners must remain diligent in dedicating their budgets toward corrosion prevention, as time is not on our side.