A Review of Pipeline Enhancements

With recent movement towards a more environment friendly way of transporting oil and natural gas, the pipeline industry is under the watchful eyes of the government and the public. Since large amounts of petroleum and natural gas are moved through pipelines, accidents involving these devices give possibility to large natural disasters. The energy industry is always trying to find ways to enhance the systems that are employed to transport energy. Advanced engineering practices are yielding innovative solutions to these historic leaking problems. 

The cause of most pipeline failure is due in part to the reduced integrity of the pipeline. Mechanical engineers design flanges, studs, bolts, and pipeline that adequately deal with mechanical processes such as pressure, and strain while chemical engineers historically protect pipelines with chemical coatings. In recent years a new way of protecting pipelines has gotten electrical engineers involved in the pipeline industry and is proving to be a very successful method of protection. This method is known as cathodic protection.

When different metals are in electrical contact through an electrolyte, galvanic corrosion may take place. This simple process is due to a direct current cell making one metal more active than the other. The metal with enhanced activity becomes the anode and corrodes, while the other metal experiences diminished activity, creating a cathode which is protected by the suppression of corrosion. This method of electrochemical corrosion control can be applied to pipeline systems in order to reduce the corrosion of the outer wall of the pipe from the elements of the earth.

There are two ways that cathodic protection can be used to inhibit the corrosive effects of nature on steel pipeline. Coupling a structure with a more active metal produces a galvanic cell where the more active metal becomes an anode and provides an electron flux to the other metal which becomes cathodic. The result is that the cathode is protected while the sacrificial anode corrodes overtime. Alternatively, the second but more complicated method involves inducing a direct current between an inert anode and the structure that is to be protected. Electrons still flow to the structure and is protected from being the source of electrons. Induced current systems bury the anode and a small direct current is applied between the anode and the cathode.

Nearly all modern pipelines are coated and used in conjunction with cathodic protection systems to prevent corrosion at holidays. Holidays are holes or gaps in the protective coating that exposes the metal surface. Since the induced current systems are more complicated to install, the capital expenses needed to supply direct current to the system are higher than for a direct connection between the anode and cathode system. When weighed against the possibility of environmental disaster, engineers are reluctant overlook these protective systems. 

Various organizations overlook the pipeline industry and provide guidelines and regulations that all corporations must follow. The National Association of Corrosion Engineers specification for buried pipelines has adopted the following criteria for determining when a steel or cast iron structure is protected by means of cathodic protection.

• A voltage of -0.85 V relative to a copper/ saturated copper sulfate electrode
• A negative (cathodic) voltage shift of at least 300 mV caused by the application of cathodic protection current
• A minimum negative (cathodic) voltage shift of 100 mV determined by interrupting the current and measuring the voltage decay
• A voltage at least as negative (cathodic) as that originally established at the Tafel segment of the E-log I curve
• A net protective current from the electrolyte into the surface

The advent of cathodic protection in pipelines has already proven to reduce corrosion on pipeline and find damaged systems before they becomes a more serious issue. Cathodic protection benefits the environment by aiding in the prevention of major oil spills and resulting trauma to local ecosystems. Corporations in the energy business also benefit by better satisfying the needs and securities of their opponents. The consumer may find peace knowing that these corporations put the interests of society in mind before the prospects of profit. There is not a single person who will not benefit in some way by implementing cathodic protection in pipelines, even if they do not use petroleum and natural gas products.