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Abstract
The impact of low-quality magnesium anodes marketed in the US, in terms of lower current efficiency and a subsequent anode life, is discussed. Testing of open-circuit potential (OCP) and current efficiency is performed in accordance with ASTM Standard Test Method, involving destructive testing of anode samples over a 14-day period. A simplified value analysis for each of the test anodes shows an impact of current efficiency on the overall annual cost of the anode. Using the mean value of 38% current efficiency derived from test data, the estimated annual cost to inventory exceeds 50,000 annually of additional cost as a result of low-quality magnesium. It is recommended that the end-users need to routinely test anodes to ensure that current efficiency specifications are being met.
This chapter covers the principles of the corrosion control methods in the discussion. Most corrosion control in oil and gas production, as well as in other industries, is by the use of protective coatings, water treatment and corrosion inhibitors, and cathodic protection. Protective coatings are the most commonly used means of corrosion control. They are the standard means of controlling external corrosion on everything from offshore structures to pipelines and process vessels. Cathodic protection is an electrical means of corrosion control where the structure to be protected is made the cathode in an electrochemical cell. The chapter illustrates a number of practices necessary to ensure successful coatings applications, inspection, and repair. Metallic coatings find limited but important uses in oil and gas operations. The most commonly used metallic coatings are zinc, thermally sprayed aluminum (TSA), and corrosion‐resistant metals and alloys such as chromium and electroless nickel.
Protective Coatings Water Treatment and Corrosion Inhibition Cathodic Protection References
This book is intended for engineers and related professionals in the oil and gas production industries. It is intended for use by personnel with limited backgrounds in chemistry, metallurgy, and corrosion and will give them a general understanding of how and why corrosion occurs and the practical approaches to how the effects of corrosion can be mitigated. It is also an asset to the entry-level corrosion control professional who may have a theoretical background in metallurgy, chemistry, or a related field, but who needs to understand the practical limitations of large-scale industrial operations associated with oil and gas production. While the may use by technicians and others with limited formal technical training, it will be written on a level intended for use by engineers having had some exposure to college-level chemistry and some familiarity with materials and engineering design.
Many of the anodes marketed in the U.S. today do not meet minimum quality requirements. This article discusses the transition of magnesium anode sources from U.S. to foreign manufacturers and points out the effects of not meeting the various quality requirements. Anode specifications should include quality standards for open-circuit potential and current efficiency as well as alloy chemistry. Operating costs for nonquality anodes exceed costs for anodes meeting quality standards, suggesting that purchasers should place more emphasis on quality and less on initial cost.