Materials Performance

MAY 2015

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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13 NACE INTERNATIONAL: VOL. 54, NO. 5 MATERIALS PERFORMANCE MAY 2015 Continued f rom page 11 THE BLOG concentrations and temperatures to be able to predict lives of tanks and piping, and also guard against accelerated corrosion in the vapor space. Pitting measurement Q: Could anyone give me a standard test method for measuring pitting potential and current on chromoly steel in an aqueous environ- ment (400 to 1,000 °C)? A: Tere are various methods of measuring potentials associated with pitting corrosion, but the most common is to use a sweep generator and potentiostat to apply a rising potential. Ten the pitting breakdown potential is that potential at which the current starts to increase rapidly, or when it passes a predefned value. Te potential sweep is then reversed (ideally at another predefned value), and the potential at which the current falls below the value on the rising part of the curve gives the repassivation potential. However, I do not think you will f ind a standard method for doing electrochem- istry at 400 to 1,000 °C. I doubt if anyone has ever done electrochemistry at 1,000 °C. It is diff icult to produce a stable reference electrode and to make reliable electrical connections to the cell. Furthermore, these temperatures are above the critical point for water, thus generally making the water a poor ionic conductor; this also makes electrochem- istry diff icult. and Coatings List Servers! More than 3,000 corrosion pro fessionals from all over the world participate on the NACE International Corrosion Network and NACE Coat ings Network. You can post your question and receive expert advice in a matter of minutes. To join either or both of these free list servers, go to the NACE Web site: nace.org, click on the "Corrosion Cen tral" link, and then "Online Corrosion Community List Servers." The networks look forward to your participation! There are various methods of measuring potentials associated with pitting corrosion, but the most common is to use a sweep generator and potentiostat to apply a rising potential.

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