The boiler volume is multiplied by the factor and the dosage of TSP is entered to the nearest one-half ounce in the appropriate space. The increase in phosphate due to TSP is given in the last column. The DSP dosages are calculated similarly using the DSP factors (ounces per gallon) given in table 7-5. TSP and DSP dosages for the aux-iliary boilers are given in tables 7-6 and 7-7. The procedures for determining the chemical treatment

Table 7-4.Trisodium Phosphate Dosage For Natural Circulation Auxiliary Boilers (Trisodium Pbosphate, Dodecahydrate, Na3 PO4 12H2 0)

Table 7-5.Disodium Phosphate Dosage For Natural Circulation Auxiliary Boilers (Disodium Phoshate, Anhydrous Na2 HPO4 )

dosages for the completed dosage tables are described below:

1. Determine the alkalinity and phosphate concentrations in the boiler water from sample results.

2. Locate the boiler water alkalinity in the first column of table 7-4. Then read across to the weight of TSP required for the correct volume. (Use table 7-6 for the vessels listed earlier in the chapter.) Enter this weight in the log.

Table 7-6.Calculated Trisodium Phosphate Dosages For Some Natural Circulation Auxiliary Boilers (Trisodium Phosphate, Dodecahydrate Na3 Po4 12H2 O)

3. Continue to the last column to find the phosphate correction. This is the amount the phosphate will increase due to the TSP. Record the phosphate correction in the log.

4. Add the phosphate correction caused by TSP to the measured boiler water phosphate. This gives the corrected phosphate concentration; record this in the log.

5. Proceed to table 7-5. Locate the corrected phosphate in the first column. Read across the table to the weight of DSP required for the correct volume. (Use table 7-7 for the vessels listed earlier.) Enter this weight in the log.

6. Weigh the chemicals, dissolve them together in the 10-liter safety dispensing bottle, and inject the solution into the boiler.

NOTE: TSP must be dissolved in cold feed-water since TSP generates heat when dissolving. DSP must be dissolved in hot feedwater if only DSP will be injected into the boiler. Therefore, TSP should be added first to cold water in the bottle, then dissolved. This will generate sufficient

Table 7-7.Calculated Disodium Phosphate Dosages For Some Natural Circulation Auxiliary Boilers, (Disodium Phosphate Anhydrous, Na2 HPO4 )

heat to dissolve the DSP when it is transferred to the TSP solution.

Remember, treatment in accordance with the DSP dosage table will not bring the phosphate level to the upper limit of 400 ppm (400 mg/L) but will only raise it to 300 ppm (300 mg/L). DSP is added to allow a margin for phosphate in case it should become necessary to treat the feedwater only for alkalinity since the addition of TSP to raise alkalinity will also increase its phosphate level. The boiler must never be surface blown if this action will cause boiler water limits to go below the minimum requirements for alkalinity and phosphate, regardless of the chloride level. A 10 percent blowdown will cause the phosphate, alkalinity, and chloride levels to drop by 10 per-cent. There are no dump limits for alkalinity or phosphate. From the standpoint of feedwater consumption, it is better to secure and dump the boiler when its alkalinity level is 6 epm (6 meg/L) or when its phosphate level is 1200 ppm (1200 mg/L).

CHLORIDE.If feedwater quality is properly maintained, a maximum concentration of 10.0 epm (10 meg/L) chloride in boiler water can be achieved without difficulty. Leakage of seawater into the feedwater system, or abnormally high makeup rates, will cause a continuous increase in the chloride level of boiler water. Boiler water chloride level is controlled by surface blowdown and by elimination of seawater contamination in the feedwater. If a serious seawater contamination situation arises, every effort must be made to isolate and correct the source of contamination and to limit it to the system already contaminated. If the boiler water chloride level exceeds 30 epm (30 meg/L), more makeup feed is needed to conduct surface blowdowns than is used in dumping, flushing, and refilling the boiler.

For additional information about boiler water/feedwater test and treatment, read chapter 220, volume 2, of the Naval Ships Technical Manual. This manual covers such subjects as (1) steam plant water chemistry principles, (2) water requirements for propulsion boilers, (3) casualty control, (4) quantitative analysis and troubleshooting, (5) chemical safety precautions, (6) supply information, and (7) water requirements for auxiliary boilers.