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FINDINGS AND OBSERVATIONS

Iron Corrosion Tests

Once steady state conditions were achieved the tests were run from March 17th through April 6th. Mil per year (MPY) LPP readings, as well as temperatures, pH, time and date, were taken daily except for Sundays. Evaporation, approximately 1½ gallon per day was made up with DI water daily, including weekends.

After makeup and before each set of readings a suitable time (ten turnovers of the system volume) was allowed for the makeup and the treatment present to become completely mixed. Samples run by the Myron L combination pH, conductivity and temperature instrument were returned to the system as they are not changed during the readings. Data from the two systems are shown in Tables I and II .

Average pH and temperatures for the two systems were reasonably close, as were the average corrosion rates. Figure 1 is a graph of the MS probe readings in the PO 4 treated system. Figure 2 is a graph of the MS probe readings in the AS-8150 treated system. Note the slope (Y) of the trendlines. Figure 1 and Table II show that the corrosion rate in the PO 4 treated system had leveled off for about the last five readings at 10 to 12 MPY. Figure 2 and Table I show that the corrosion rate in the AS-8150 treated system had leveled off for about the last four readings at 3 to 5 MPY.

This may be explained by the fact that the PO 4 3- ion was ready to go to work immediately, forming a calcium phosphate or iron phosphate deposit on some of the areas on the probe; whereas the AS-8150, by what ever chemical or physical mechanism it works, took longer to form its protective barrier. Figure 3 shows Figures 1 and 2 on a single graph. It is unlikely that the curve or the trendline for the PO 4 corrosion rate would have reached the low rate achieved by the AS-8150.

The coupons and probes were removed from the systems at the end of the test. The mild steel coupons and probes from both systems, before cleaning, are shown in Photo #3. The three AS-8150-theated specimens are on the left. Closeups of the probes and coupons, before cleaning, are shown in Photo #4. The deposits on the MS specimens from the AS-8150-theated system were darker than those in the PO 4-treated system, see Photos #3 & 4. This may indicate reduction of the ferrous and/or ferric oxide(s) to the magnetite form.

The cleaned MS corrosion coupons show a story similar to the graphs. Photo #5 shows the two pairs of coupons after the final cleaning with inhibited 6 N hydrochloric acid. Photos #6 through #9 [#6, #7, #8, #9] show the PO 4-treated coupon close-up and turned over. Photos #10 and #11 show the AS-8150-treated coupons turned over and close-up, respectively.

The types of corrosion that occurred in the two systems appear to be quite different. The coupons from the PO 4-treated system show localized attack and are gouged. The coupons from the AS-8150-treated system show more of a general etch. Both sets show crevice corrosion under the coupon holder and bolt and nut.

The deposits on the MS specimens from the AS-8150 treated system effervesed vigorously when cleaned with 6 N Hydrochloric acid, indicating carbonate. The deposits on the MS specimens from the PO 4 treated system produced very little gas evolution.

The AS-8150-treated coupons had greater weight loss and hence higher MPY corrosion rates than the PO 4-treated coupons: Figures 1 & 2 explain this. The weight loss includes the metal taken off by the initial corrosion. It is customary to pretreat a new or cleaned system with dosages of the inhibitor several times its expected maintenance dose. This was not done. However, at 10 mg/LPO 4 as PO 4 the test started out at a not-much-higher rate than it finally achieved, while the AS-8150 required several days to catch up with the PO 4.

At the completion of the test the test waters were sampled and analyzed as seen in Columns D and E, Table III, along with the makeup and the original test waters.

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