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1950-51 Theatre Catalog, 9th Edition, Page 373 (351)

1950-51 Theatre Catalog, 9th Edition
1950-51 Theatre Catalog
1950-51 Theatre Catalog, 9th Edition, Page 373
Page 373

1950-51 Theatre Catalog, 9th Edition, Page 373

Preventing Corrosion in Air-Conditioning System

Chemical Compounds for Warding Off or Reducing Destructive Formations Are Helpfully Analysed

Operating air-conditioning and refrigerating systems is easier when corrosion is kept under control. Beyond the direct damage it does from contact of water and brine with the equipment-pipelines, pumps, spray chambers, cooling towers, condensers, etc.-there is the effect the corrosion products have on performance. Rust and bits of corroded metal clog up spray nozzles and heat-exchanger passes.

The problem is aggravated by electrolytic or galvanic action at points of contact between the different metals used in construction of the equipment. Letls look at the factors involved and the steps to control corrosion.

Raw Wafer

Most natural waters are corrosive to metals, especially the softer Waters and those containing only small amounts of alkaline salts in solution. Artesian-well waters tend to be particularly corrosive

BRIEF: Corrosion . . . in a cooling system . . . is one difficulty that need not be tolerated . . . Needless damage can readily be avoided by knowing the required chemical makeup of the circulating solution . . . be it water or brine . . . The important thing is to make it non-corrosive . . . and hold the concentration of the preventive compound at the proper level . . . by frequent water analyses . . . and regularly adjusted feeding of chemicals.

The following article . . . written by an executive of an organization specializing in such problems . . . discusses the most effective treatments for corrosive water in air-conditioning systems . . . brine solutions in refrigerating units . . . and scale prevention under hard water conditions . . . It is obvious that a wise chemical treatment program . . . such as the author advocates . . . will give a longer lease on life to any type of air-conditioning equipment.

because they carry such large quantities of dissolved carbon dioxide'(CO:). This natural corrosiveness of water increases in cooling towers, air washers and evaporative condensers because water absorbs air and impurities in it-carbon dioxide, sulphur dioxide from smokestacks, etc. Most effective treatment for water in air-conditioning systems involves (1) raising pH with an alkali (2) forming a passivating film on metal surfaces by adding sodium chromate. Complete corrosion protection results from keeping the proper concentration of chromate in the water, plus a pH of about 8.5 at all times. To do this means frequent water



Technical Manager. Water Service Laboratories, Inc.

analyses and regularly adjusted feeding of chemicals.

Control of pH has a direct bearing on rate of corrosion. Without going into the derivation of the term pH it can be stated that, within limits, the higher the pH, the less corrosive the water, and vice versa. Most city waters have a pH of about 7.0 unless the city applies some special treatment to its water. If it adds some material like lime or sodium silicate, the pH will probably be 8.0 or a little higher. In steam boilers where alkaline chemicals are added to prevent scale and corrosion, boiler-water pH is

*Reprinled from, July, 1949 inue 0/ POWER.

usually between 10.5 and 11.5, or higher.

Lets see what happens to the water in air-conditioning equipment. Air washers, Fig. 1, pass air through a chamber where water circulates as a spray. The water has undergone cooling in a refrigerating system. The cold-water spray washes dust and impurities out of the air and condenses some of the entrained moisture. This cooling and lowering of the humidity in the air is one of the primary objectives in comfort air conditioning.

But this spray water continually absorbs carbon dioxide from the air so the pH falls and the water tends to become very corrosive. Unless chemical treatment is used to hold up the pH, corrosion can proceed apace. To a lesser degree, water passing through evaporative condensers or cooling towers experiences the same change in pH.

FIGURE l-Simple air washer cools and lowars humidity oi incoming air-a primary obiective of airconditioning-but the cooling water becomes higle corrosive.

FIGURE 2-When you take the absorbed heal out oi the spray water with a refrigerant you add a condenser cooling-water circuit that needs protection against corrosion.

1950-51 Theatre Catalog, 9th Edition, Page 373