Water treatment corrosion inhibitors

Appropriate chemical treatment of water (with corrosion inhibitors, dispersants, and filmers)... 

Water-soluble corrosion inhibitors are necessary to prevent corrosion of the pipe walls, joints, pumps, and collection stations. An ampholytic, substituted imidazoline has been described for inhibiting corrosion in such systems [297]. This type of corrosion inhibitor is intended for continuous treatment. 

System reliability is of the utmost importance to water suppliers and their customers. However, corrosion problems can vary greatly within a single system because many variables affect corrosion, for example, pipe material, pipe age, pipe wall thickness, water additives, corrosion inhibitor treatment, soil chemistry, soil moisture content and/or local groundwater level, and stray currents [2]. Table 8.2 summarizes some of the physical, environmental, and operational factors that can affect the deterioration rate of water distribution systems and lead to their failrue [4]. 

Uses Corrosion inhibitor tor open recirculating cooling water tems and process water treatment scale inhibitor tor heat exchangers and system surfaces contains dispersants to clean up fouled or scaled systems Features Rec. dissolved solids in system be maintained at 3-5 rycles of cone. 

Chem. Descrip. Syn. and org. polymers and zinc corrosion inhibitors Uses Cooling water treatment, corrosion/scale inhibitor, dispersant for cooling towers cleans existing scale deposits and prevents further scaling Features Rec. for cooling towers utilizing makeup water that is < 10 grains/gal (170 ppm) total alkalinity... 

Oxygen Scavenger Corrosion Inhibitor Figure 10.23 Injection water treatment scheme... 

Alkyl or aryl phosphonates, which contain a carbon—phosphoms bond, are comparatively more stable. They are of interest as antiscaling additives and corrosion inhibitors for cooling towers and heat exchangers (see Dispersants Water, industrial water treatment), surfactants (qv), sequestrants, and textile-treating agents. Trialkyl phosphites are usehil as esterification (qv) reagents. 

Organophosphonates are similar to polyphosphates in chelation properties, but they are stable to hydrolysis and replace the phosphates where persistence in aqueous solution is necessary. They are used as scale and corrosion inhibitors (52) where they function via the threshold effect, a mechanism requiring far less than the stoichiometric amounts for chelation of the detrimental ions present. Threshold inhibition in cooling water treatment is the largest market for organophosphonates, but there is a wide variety of other uses (50). 

Chemical inhibitors, when added in small amounts, reduce corrosion by affecting cathodic and/or anodic processes. A wide variety of treatments may be used, including soluble hydroxides, chromates, phosphates, silicates, carbonates, zinc salts, molybdates, nitrates, and magnesium salts. The exact amount of inhibitor to be used, once again, depends on system parameters such as temperature, flow, water chemistry, and metal composition. For these reasons, experts in water treatment acknowledge that treatment should be fine tuned for a given system. 

Recommendations were made to begin treatment with corrosion inhibitors and to make system operation changes to reduce grease and oil fouling. Other water chemistry recommendations involved reducing the amount of aggressive anion in solution and pursuing biocidal treatment. 

The susceptibility of nickel alloys, principally Alloys 600 and 800 to stress-corrosion in water-cooled nuclear reactor heat-exchanger circuits has received much attention. The influence of both metallurgical variables (e.g. alloy composition, heat-treatment) and water chemistry (additives, inhibitors) have been extensively studied and reviewed. ... 

Industrial Cooling Water Systems Waters used for recirculating cooling systems can either be scaling or corrosive. Corrosive waters are treated with corrosion inhibitors which require monitoring for overall assessment of the treatment programme. 

JJ..L . Co itioniagaheAimosphere4o Redue AS j 5 .t Qtrssionjafaifaitkm >Erinciples nd. jactiee -, n.3 The Mechanism of Corrosion Prevention by Inhibitors 17.4 Boiler and Feed-water Treatment... 

In all space heating boiler systems there is a tendency to keep water treatment programs as simple as possible. Ideally, chemical inhibitors should be added in proportion to MU demands, metered water consumption, oxygen content, or other preemptive measurement. More typically, the standard process is to periodically (weekly to monthly) analyze the BW for a few basic control parameters, including measuring the multimetal corrosion inhibitor reserve, and then to merely top-up the inhibitor when the reserve is below the minimum specification. Chemical treatment often is added directly to the BW by hand-pump via a hose cock (bib cock) connection. 

Where water softening is provided and there is no reduction in system water TDS, treatments are primarily based on inorganic corrosion inhibitor blends (nitrite, molybdate, etc.). Under these circumstances, there is no benefit in using an expensive organic oxygen scavenger to keep the TDS level low, and a common chemical such as catalyzed sodium sulfite may be used. 

Because of their surfactant and filming properties fatty amines such as coco-alkylamine acetate (and more especially diamines, such as tallow propylenediamine) are also occasionally employed in other types of water treatment programs. For example, they may be used as corrosion inhibitors for steel cooling systems, especially those smaller units where minimal operational control is provided. The amines must be continuously dosed to ensure good film formation (and thus corrosion protection), typically at 5 to 10 ppm active amine. They also tend to have good biostatic control properties, which provide a benefit of algal and bacterial control at no extra cost. 

Gandhi, Ashish (Cortec Corporation). Volatile Corrosion Inhibitors Unique Water Treatment Applications. The Analyst, Journal of the Association of Water Technologies, USA, Fall 2000. 

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