Materials Performance Supplements

CORTEC 2018

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.

Issue link: https://mp.epubxp.com/i/987623

Contents of this Issue

Navigation

Page 10 of 23

the management of chemical substances to minimize major adverse effects on human health and the environment by 2020. The International Conference on Chemicals Management in 2006 adopted the Strategic Approach to International Chemicals Man- agement designed to implement the Johan- nesburg Plan. 1 In 2007, the European Union implemented the Regulation on Registration, Evaluation, Authorization, and Restriction of Chemicals to achieve the World Summit on Sustainable Development goals by 2020. These factors led to the introduction of alternative oxygen scavengers includ- ing amine-compounds, diethylhydroxyl- amine, 10-14 helamine (amine-based com- p o u n d s) , 1 5 - 1 8 su r fa c e - a c tiv e fatty al ky l polyamines, and amines of different vola- tility (cyclohexylamine + aminoethanol + (Z)-N-9-octadecenylpropane-1, 3-diamine), an d c yclo h e xy l amin e-b a sed c or ro sion inhibitors. 8-9, 19-24 These amine-based com- pounds were introduced as an alternative oxygen scavenger to hydrazine, offering the advantages of very low toxicity and the vola- tility of a neutralizing amine. Like hydrazine, amine-based compounds also promote the formation of a passive magnetite film on low carbon steel (CS) surfaces, minimizing cor- rosion in the system. 11 Amine-based water treatment has numerous beneficial proper- ties as an oxygen scavenger in boiler feed- water systems: protects by forming a thin magnetite oxide (Fe 3 O 4 ) layer ; prevents lime scale or minerals on surface installations; removes old deposits without causing dam- age; disperses impurities, inorganic salts, and oxides of iron; alkalinizes vapor net- works, including the return of condensate and hot water systems; and provides effec- tive heat transfer and energy savings. The operating parameters of the boiler systems (pressure, temperature) are very important in determining how much inhibitor is required to maintain an acceptable corro- sion rate level (<1.0 mpy). In low to moderate pressure industrial boiler systems, an initial feedwater inhibitor dosage of 100-500 mg/L is recommended. 17 However, during operation an adjusted product feed rate is used until a consistent inhibitor residual of 80-120 mg/L can be established in the condensate. Volatile Corrosion Inhibitors Volatile corrosion inhibitors (VCIs) are compounds transported in a closed loop environment to the site of corrosion by vol- atilization from a source. In boilers, volatile basic compounds, such as morpholine or hydrazine, are transported with steam to prevent corrosion in the condenser tubes by neutralizing acidic carbon dioxide (CO 2 ) or by shifting surface pH toward less acidic and corrosive valu es. 15-18, 20-25 In closed vapor spaces, such as shipping containers, volatile solids such as salts of dicyclohex- ylamine, cyclohexylamine, and hexamethy- lene-amine are generally used. When these inhibitors come in contact with the metal surface, the vapor of these salts condenses and is hydrolyzed by any moisture to lib- erate protective ions. It is desirable, for an efficient VCI, to provide inhibition rapidly while lasting for long periods. Both quali- ties depend on the volatility of these com- pounds; fast action wanting high volatility while enduring protection requires low vol- atility and complex compound formation. In addition to oxygen scavenging and metal passivating capabilities, another key advantage of amine-based inhibitors is their volatility. Not only do they scavenge oxygen and passivate metal in the feedwater and boiler portions of a steam boiler cycle, they also cause evaporation or dispersion by vapor phase (volatilize) with the steam to provide complete system protection. The fact that the amine-based compounds are volatile represents an enormous advantage in condensate system treatment because most of it is transported and absorbed into the condensate system, allowing it to passivate condensate system metallurgy, preventing corrosion; scavenge oxygen if it enters the condensate system, prevent- ing corrosion; reduce corrosion byproduct transport to the boiler, minimizing the potential for boiler deposition and under- deposit corrosion; improve equipment reli- ability and efficiency ; and minimize overall condensate system corrosion, reducing the related maintenance costs. Research Objectives Corrosion of the steam/waterside inte- riors during the various stages of the steam cycle is a major problem for steam-generat- ing and power plant operators. The industry standard for corrosion protection in operat- ing systems is the use of hydrazine required to be limited per the European Union. Amine-based compounds are considered an alternative to hydrazine. These amines are normally injected into the steam line but may be injected into the boiler water or the con- densate system. The purpose of this investi- gation was to compare the performance of the new amine-based VCI vs. the hydrazine capabilities to provide corrosion protection for the boiler steam/water system internal surfaces through the phases of the steam sys- tem (water, transition, steam). Prior to inves- tigating this new VCI in a closed loop system, some preliminary testing was conducted at high temperature (roughly 182 °C [357 °F) to determine when it would start to boil; the hydrazine boiling point is 114 °C (238 °F). The assumption was that if hydrazine can survive the steam cycle, then this new VCI FIGURE 1 Corrosion behavior of the steel pipe samples in boiling water. Corrosion rate decreased to 1.36 mpy with 100 and 500 mg/L VCI addition (700 h). 11 CORTEC SUPPLEMENT TO MP MATERIALS PERFORMANCE JUNE 2018

Articles in this issue

Archives of this issue

view archives of Materials Performance Supplements - CORTEC 2018