Cooling water system deposits

Attack always occurs beneath a deposit. Cooling water system deposits are ubiquitous. Deposits can be generated internally as precipitates, laid down as transported corrosion products, or brought into the system from external sources. Hence, underdeposit corrosion can be found in virtually any cooling water system at any location. Especially troubled... 

Almost all cooling water system deposits are waterborne. It would be impossible to list each deposit specifically, but general categorization is possible. Deposits are precipitates, transported particulate, biological materials, and a variety of contaminants such as grease, oil, process chemicals, and silt. Associated corrosion is fundamentally related to whether deposits are innately aggressive or simply serve as an occluding medium beneath which concentration cells develop. An American... 

Cooling water systems are dosed with corrosion inhibitors, polymers to prevent solid deposition, and biocides to prevent the growth of microorganisms. 

Calcium carbonate makes up the largest amount of deposit in many cooling water systems (Fig. 4.16) and can be easily detected by effervescence when exposed to acid. Deposits are usually heavily stratified, reflecting changes in water chemistry, heat transfer, and flow. Corrosion may be slight beneath heavy accumulations of fairly pure calcium carbonate, as such layers can inhibit some forms of corrosion. When nearly pure, calcium carbonate is white. However, calcium carbonates are often intermixed with silt, metal oxides, and precipitates, leading to severe underdeposit attack. 

Siiica S1O2 Scale in boilers and cooling water systems Insoluble turbine blade deposits due to silica vaporization Hot process removal with magnesium salts adsorption by highly basic anion exchange resins, in conjunction with demineralization distillation... 

NOTE The view that deposition is an indicator of more widespread problems is also common to cooling water systems. As a result of the complex nature of deposits, their removal by acid or mechanical cleaning of boiler or cooling systems is not always as simple a process as may be portrayed. 

Troscinski, E, S., and R, G. Watson, Controlling Deposits in Cooling Water Systems, Chemical Eng. (March 9, 1970). 

NOTE In this chapter there is discussion concerning some individual aspects of corrosion, fouling, and deposition, but every attempt is made to link them together into a coherent whole. It is also incumbent upon the reader and water treatment practitioner to consider each specific problem or aspect of water management in the light of the complete, dynamic, cooling water system. 

Biofouling. Deposits formed when biological mechanisms attach and grow on the heat transfer surface. Untreated cooling water systems are particularly susceptible to biofouling. 

Veale, M.A., 1984, Control of deposits in cooling water systems, in Fouling and Heat Exchanger Efficiency. Continuing Education Course. Instn. Chem. Engrs., University of Leeds. 

The choice of material of construction will influence the extent of possible corrosion and may affect the retention of other deposits, for instance corrosion resistant titanium tubes have been known to foul more rapidly than some stainless steel alloys under similar conditions. It is unlikely in large cooling water systems, e.g. power station condensers, that treatment of the heat exchange surfaces will be considered as a feature for the reduction of fouling, due to the relatively high costs involved including initial cost and maintenance. 

It is valuable to provide connections on the cooling water system, that may be used for flushing to dislodge any accumulations of deposits that might occur. The opportunity to isolate heat exchangers by the inclusion of bypass systems, must be included so that off-line cleaning can be carried out without the need to shut down whole sections of the total cooling water circuit. 

Corrosion in a Cooling Water System Cooling water tubes are used extensively in industry. Corrosion of cooling water tubes or pipes is a common phenomenon. The heat exchanger was opened to examine the extent of corrosion. Heavy deposits were revealed inside the tubes (Fig. 5.30). Isolated but deep pits were present under the hard deposits (Fig. 5.31). 

Uses Scale inhibitor for cooling water systems, boilers, and in oil fields to control calcium, barium, magnesium, strontium, and iron scale deposits... 

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