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378 CHAPTER 21 1965 Guide And Data Book The use of'certain oxidants such as' sodium chromate in conjunction withglycol 'solutions should be avoided, as pre mature oxidation of. the glycol can occur.. Generally, combi^ nations of the two types' of additives,' inhibitors and'stabilisers, offer the best corrosion resistance in a given system. Com mercial inhibited glycols for various applications are available from several suppliers. - Service Considerations , V...' Storage and Handling. Inhibited'glycol concentrates`'are stable,' relatively 'noncerrosive - materials ' with' high i flash points. Under some conditions they can be stored in'mild steel, though'stainless steel or aluminum vessels of even-containers lined with a baked phenolic or-vinyl resin coating' may be required: Regarding Container selection/ H should be pointed out that the chemical properties of an inhibited'glycol eon-' centrate can be substantially different from that of its dilu tion, and therefore the effect of the concentrate on the par- ticular container components in contact with the glycol should be known:, :Transfer.pumps should be' chosen only after consideration of. the temperature-viscosity' data. Centrifugal pumps: with electric motor drives are often recommended. Rubber-impreg nated asbestos of its equivalent is considered a suitable pump packing material; a mechanical seal may/also be satisfactorily, employed. Transfer piping of. mild<'steel with a minimum diameter of two inches is generally suggested. Welded con struction is normally used in conjunction with the piping, although flanged and gasketed, joints, are also.satisfactory. ' Preparation Prior to Appftdati<ro-:Before an inhibited glycol Secondary Coolants (Brines) 379 harrad into a new or old system, residual contaminants . " 1 m Judge, rust, brine deposits, oil, etc., shouU be re- ""Li is completely us possbile, in Older that the contained tohibitor may function property. It is generally better to avoid use of strong acid cleaners; however, if they are required, vhihited acids should be considered. In any.event, care should {"taken to insure that (he cleaning.agent is"completely re moved before charging with inhibited glycol. - . Ttie quaiity-of the water; of dilution must be considered, because water, from rome'sources may contain corrosive ele- menta which reduce.the .effectiveness of the inhibited formula tion. Preferably, surface waters that are classified as eofi and are low in chloride..and sulfate ion.content (less.than 100 npm each) should be: employed. The use-of distilled, deionised, or condensate water should help to-avoid the undesirable effects of poor quality.water. ,- The decision to employ an inhibited glycol should be con sent with potential temperature factors. In systems-where a high degree of'aeration is 'encountered, a maximum bulk fluid temperature of 180 F is proposed, but up to 250 F may be permissible in a pressurized system if air intake is-bept to a mirimiim skin temperatures should not exceed 300-325 F, and should be even lower if the hot wall surface area is luge in proportion to the quantity of flujd circulated. Nitrogen blanketing is often helpful in minimising.oxidation when the system is operating at elevated temperature tor.ex tended periods. . From the low.-temperature-standpoint,; operation :below -- 60 F is not, recommended,.although slightly .tower;,tem peratures may be tolerable in certain operations .where tbe solution temperature is cycled periodically to a higher level. It is usually advantageous to install suitable filters, as the removal of active sludge and other! contaminants may be critical It has been noted that, in some instances, inhibitors have been rapidly and completely adsorbed by such contemhnation,"'thereby leaving- the-fluid ineffective-for:corrosion inhibition.* Such adsorption should -be considered whep-so- lecting a filter. -. - / V* Inhibitor Maintenance. One of .the mostimportentaspects in'maintaining a' glycol solution in-a relatively-noncorrodve condition over a! tong period of time is the inhibitor monitor ing and maintenance tehediile. The'desirability of establishing and maintaining a satisfactory inhibitor level cannot be over- Table 4 . Freezing and Soiling Points cf Ksnn.srbw<i Coolants No.' - tahiaarant Name 12 .11 30 1120 Dichlorodifluoromethane - Trichloromonofiuoromethane 'Methylene Chloride Trichloroethylene FieoWng f' -252 --108 -142 -123 Point, f -21.6 74.8 103.6 188.4 pmpKamzpd. However, a specific schedule is not always easy to establish, smee the rate of inhibitor depletion depends upon the~particular conditions of use. Analyses of samples immedi ately after installation, after 2 to 3 months service, and after 6 rr>nntha1 should establish the pattern for such a schedule. Visual inspection of the solution and filter residue iB often helpful in judging whether or not active corrosion is occurring. In general, properly, inhibited and .properly maintained glycol solutions should provide advantages in'corrosion pro tection as compared to brine solutions in most systems. An indefinite service life, however, should- not be expected. The preservation:of costly equipment is, perhaps,- the.chief.ad vantage of.these materials. Indiscriminate mixing of inhibited formulations should.be avoided unlem known to be compatihle.-In this connection, the replacement of brine systems with inhthitpd glycol should be approached -with caution because of.the potential incompatibility of the brine components with these glycol formulations. HAlbCARBONS ''Many. of. the common'refrigerants can be'employed as 'Secondary' coolants as'well as'primary refrigerating media. Favorable properties for applications as heat .transfer fluids i~nt1nHft' low freezing points, low viscosities, nonflammability, 'and good stability. Physical and thermodynamic properties for all the:eommon refrigerants are presented in Chapters 19 Rg.c'18-.'^i. Specific Heat-of.AqueousrSolutions of Propylene: Glycol Rg.! 20 '.Thermal .Conductivity-of- Aqueous, Solutions -of Propylene .Glycol fifl- 21 .... Thermal Conductivity of liquid Halocarbon Coolants Fig. 22 .... Density of liquid Halocarbon Coolants