UFC 3-240-13FN
25 May 2005
3. Add sodium hydroxide (caustic soda) to maintain a pH of 8.5 to 9.5. It is
likely that a buffer will be needed for pH control in this range.
4. If copper is present, maintain a minimum of 10 ppm of tolyltriazole.
5. Test monthly for proper pH and molybdate levels.
5-2.2.4
Molybdate-Nitrite-Azole Treatment Program. This program is not
recommended for use in systems in which water temperatures exceed 121 C (250 F).
An effective approach for corrosion control in these systems involves a program that
combines elements of the molybdate program and the nitrite program. The targeted
maintenance level for the combined addition of molybdate and nitrite is about half of
what either would be for individual addition. Most water treatment service companies
offer this chemical combination as a formulated product. This chemical treatment
program is also compatible with ethylene glycol or propylene glycol. A recommended
procedure for maintenance of the system consists of five steps:
carbonate).
2. Control the nitrite-molybdate-azole compound to maintain a nitrite level of
300 to 400 ppm (as NO2), a molybdate level of 50 to 75 ppm (as Mo).
Avoid this program if (CL + S O4) concentration exceeds [(NO2 + MO)-
100]ppm.
3. Add sodium hydroxide (caustic soda) to maintain a pH of 8.5 to 9.5. It is
likely that a buffer will be needed for pH control in this range.
4. If copper is present, maintain a minimum of 10 ppm of tolyltriazole.
5. Test monthly for proper pH and treatment levels.
5-2.2.5
Polysilicate-Azole Treatment Program. This program is not
recommended for systems where water temperatures exceed 121 C. This program is
especially beneficial when aluminum metal is present. Aluminum is rarely found in
comfort heating and cooling systems, but is sometimes found in closed process cooling
water loops or diesel engine jacket systems. Aluminum will corrode at high pH, so the
pH of the system water must be closely monitored if aluminum is present. This chemical
treatment program is also compatible with ethylene glycol or propylene glycol. A
recommended procedure for maintenance of the system consists of five steps:
carbonate).
2. Control the treatment to maintain a polysilicate level of 80 to 100 ppm (as
SiO2).
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