Materials Performance Supplements


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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Hydrazine is used as an oxygen scaven- ger to control corrosion in steam-gen- erating systems, despite being a geno- toxic carcinogen. Alternative chemicals, nontoxic corrosion inhibitors, or new oxygen scavenger-free water treatment technologies are preferred. A newly de- veloped amine-based vapor phase cor- rosion inhibitor (VCI) was investigated. Electrochemical tests were conducted and showed a significantly lower corro- sion rate in steam-generating boilers and boiling water. Short-term (720-h) corrosion tests in boiling water showed a decreased corrosion rate from 5.3 mpy to 1.93 mpy for 50 mg/L VCI and 1.32 mpy (0.001 metal loss per year) for 100 mg/L VCI addition. Long-term (2,200-h) corrosion tests in the hot steam-generating closed loop system showed a decreased corrosion rate from 8.2 to 8.9 mpy for the control sam- ple to 0.72 to 0.74 mpy when washed with 500 mg/L VCI solution. The closed loop system was subsequently main- tained at 100 mg/L inhibitor for the test remainder. Inhibitor added at the be- ginning of the test resulted in a corro- sion rate of 1.09 to 1.24 mpy (with 100 mg/L VCI). X-ray photoelectron spec- Amine-Based Vapor Phase Corrosion Inhibitor Alternatives to Hydrazine for Steam-Generating Systems and Power Plants Behzad Bavarian and Lisa r einer, California State University, Northridge, California, USA James h o L den and Boris a . m iksic, F nace , Cortec Corp., St. Paul, Minnesota, USA VAPOR PHASE CORROSION INHIBITORS troscopy analysis showed that the amine-based inhibitor promoted and stabilized a protective magnetite oxide (Fe 3 O 4 ) on the pipe internals. This inves- tigation confirmed the inhibitor can be an effective replacement for toxic hy- drazine. Th e presence of di ssolved oxygen in metal boiler feedwater and steam-generat- ing systems can present serious problems in a steam-generating plant by promoting corrosion and thick scale formation in the feedwater system, the boiler, and the steam condensate system. Therefore, it is important to remove oxygen from the feed- water and also from the condensate where in-leakage can occur. The first step in the elimination of oxygen from the boiler feed- water is mechanical deaeration. The sec- ond step involves chemical oxygen scav- enging to remove the residual oxygen. For many years, sodium sulfite and hydrazine were the preferred chemical oxygen scav- engers. However, sodium sulfite contrib- utes solids to the boiler water and hydra- zine was found to be extremely toxic. Hydrazine has been used as an oxygen scavenger and corrosion inhibitor for cor- rosion control in steam-generating sys- tems. Although hydrazine is very effective, it is a genotoxic pollutant. The use of alter- native chemicals such as nontoxic corro- sion inhibitors, oxygen scavengers, or new oxygen scavenger -free water treatment technologies is highly recommended and in most countries required by law. Prohibiting the use of hydrazine requires the availabil- ity of nontoxic alternatives for water treat- ment technology without oxygen scaven- gers. 1-9 Hydrazine-free water treatment provides the following advantages: reduc- tion in environmental impact and improve- ment of the work environment; reduction in deposition, which in turn reduces the fre- quency of chemical cleaning for through- flow boilers; reduction in pipe wall thinning due to f low-accelerated corrosion ; and reduction in startup time and water con- sumption in the drum boilers and heat recovery steam generator boilers. Restrictions on the Use of Hydrazine In recent years, an international frame- work for the control of chemical substances has been created. In 1992, the United Nations Conference on Environment and Develop- ment adopted the Earth Summit Agenda 21, 3 a global action plan for sustainable development in the 21st century. In 2002, the World Summit on Sustainable Devel- opment adopted the Johannesburg Plan of Implementation containing guidelines on 10 JUNE 2018 MATERIALS PERFORMANCE CORTEC SUPPLEMENT TO MP CORTEC SUPPLEMENT TO MP

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