Civil Engineering Reference
In-Depth Information
TABLE 21-12. AWWA Standards for Corrosion Inhibitors
AW WA
Standard No.
Chemical Covered
Soda ash
B201
Quicklime and hydrated lime
B202
Liquid sodium silicate
B404
Caustic soda
B501
Sodium hexametaphosphate
B502
Sodium tripolyphosphate
B503
Carbon dioxide
B510
Calcium carbonate
Not covered
Half-burnt dolomite
Not covered
Monosodium phosphate, anhydrous
B504
Disodium phosphate, anhydrous
B505
phosphate inhibitors used in potable water systems. The polyphosphates may be pro-
duced and purchased as plates, flakes, lumps, beads, and fine or coarse granular or
powdered forms. The material is soluble in 50
F (10
C) water at one part to four parts
water, and the pH of a 1 percent solution is in the range of 5.8 to 7.3. Hexameta-
phosphate is available in crystalline form for dry feeder or solution feeding. It is also
available in a slowly soluble vitreous form for use in pot feeders in small water sys-
tems.
The chemicals most frequently used to control corrosion are listed in Table 21-11
along with application and solubility data.
The AWWA has established standards to define the allowable impurities for most
of the common corrosion-control additives (Table 21-12).
TABLE 21-13. Comparative Costs (1994) of Corrosion Inhibitors
Treatment Cost,
$ / mil gal
Lime 10-30 0.02 2.00-6.00
Caustic soda 10-30 0.20 10.00-15.00
Soda ash 10-30 0.12 16.70-50.00
Sodium hexametaphosphate 1-4 (PO
4
) 0.90 (PO
4
) 7.50-30.00
Bimetallic phosphate 0.5-2 (PO
4
) 1.50 (PO
4
) 6.25-25.00
Zinc orthophosphate 0.1-0.5 (Zn) 2.25 (Zn) 2.00-25.00
Sodium silicate 4-10 (SiO
2
) 0.30 (SiO
2
) 10.00-25.00
Carbon dioxide 5-10 0.05 2.00-4.00
Phosphoric acid 0.5-3 (P) 0.60 (PO
4
) 3.00-18.00
Monosodium phosphate 0.5-3 (P) 1.20 (PO
4
) 6.00-36.00
Ortho-polyphosphate blend 0.2-1 (PO
4
) 2.50 (PO
4
) 4.00-20.00
Source:
The above data were taken from a comprehensive guide on determining corrosion costs, corrosion-
control chemical costs, and benefit-cost analysis in water distribution systems; see Reference 53.
Note:
To obtain $ / kg, multiply $ / lb by 2.20. To obtain $ / m
3
, multiply $ / mil gal by 0.000264.
Dosage Rate,
mg/L
Inhibitor
Cost, $ / lb
Type
