Materials Performance Supplements

CORTEC 2019

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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FIGURE 1 Cyclic polarization behavior of UNS G10180 steel in 1.0% VCI-A at different aqueous solutions. FIGURE 2 Cyclic Polarization behavior of UNS G10180 steel in 1.0% VCI-B at different aqueous solutions. any one or a combination of these mecha- nisms may reduce pipeline service life and in extreme cases make it unfit for purpose. With the growing shortage of fresh water resources, it is often preferrable to utilize seawater as supplement water of recirculat- ing cooling water systems. 2-3 But seawater is an electrolyte solution with multiple salts, mainly 3.0 to 5.0% sodium chloride (NaCl); a pH value of ~8; and dissolves a certain amount of oxygen. 1 Due to its chemistry, sea- water easily corrodes pipelines. So the key to seawater utilization is to solve piping and equipment corrosion problems in the seawa- ter environment by modifying its chemistry with the addition of corrosion inhibitors. Corrosion and corrosion inhibition of steel have received enormous attention for recirculating cooling water systems. 5-7 The common methods to control and prevent metal equipment corrosion are using resis- tant material, using a cooling water anticor- rosion coating, increasing the pH value of the cooling water operation, and adding cor- rosion inhibitor. 6-9 Among these methods, using resistant material can protect metal equipment effectively, but the expense is too high. The technology of an anticorrosion coating method is complex and applies to local anticorrosion in the system. Increasing water pH makes mild steel deactivate easily. Adding corrosion inhibitor can protect the system and it is economical and practical. 7 After the completion of a hydrostatic test, the water must be discharged, often with environmental considerations due to toxic- ity or excessive chemicals when inhibitors are added. 8 The development of seawater corrosion inhibitor goes from inorganic to organic, from single to compound, from single inhi- bition type, to mixed inhibition type and other electrochemical method combination processes. 8 Many organic molecules exhibit high anticorrosion potential, but they pol- lute the environment during their synthesis and applications. 7-9 The effect of a single sea- water corrosion inhibitor is unsatisfactory in general, so two or several types used in conjunction improve inhibition efficiency. Therefore, to control corrosion and bac- terial growth in the pipeline during hydro- static pressure tests and future storage, the test water may be treated with corrosion inhibitors and other chemical compounds to manage and control corrosion activities. Commonly used chemicals are biocides that kill the micro-organisms and prevent the formation and growth of bacteria and other organisms in the seawater. Corrosion inhibitors are used to retard general corro- sion when residual oxygen is available, and oxygen scavengers are used to reduce the amount of oxygen available for corrosion and bacterial growth. Different classes of corrosion inhibitors may be used to pro- tect systems from corrosion , including inorganic or organic. Inorganic inhibitors include nitrites, phosphorous-based com- pounds, and others. Organic inhibitors are the products formulated from molecules constructed from of carbon , hydrogen , oxygen, and nitrogen atoms. Vapor-phase corrosion inhibitors (VCIs) described in this article are organic-based blends. The mechanism of the corrosion protection of organic inhibitors includes the formation of a thin, sometimes monomolecular layer on the metal, which is a protective barrier to aggressive ions. 4-5 In the majority of cases, 7 CORTEC SUPPLEMENT TO MP MATERIALS PERFORMANCE JUNE 2019

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