WATER TREATMENT

year for six to seven days with only the initial dose .

Several amine residual tests were taken over the 11-day period after the initial 10-ppm dose . A rose bengal test method for aliphatic amines was used , measuring absorbance at 560 nm with a Hach DR890 spectrophotometer . 3.5 hours after the application of the initial dose , a sample was tested yielding a residual level of 7.96 mg / L . Another sample was tested at 5.5 hours , indicating that 5.03 mg / L of FFA remained , nearly a 40 % loss .

A correlation can easily be seen in the first few days of testing between residual FFA and corrosion rates . Corrosion rates sharply decline as the film begins to form in the first two days . From day two to day eight , corrosion rates remain relatively steady as residual filming amine slowly decreases to < 0.2 mg / L .

At day seven , a residual of 0.06 mg / L was measured without a noticeable increase in corrosion rate . Not until the final measurement of 0.03 mg / L was there a corresponding increase in corrosion . Testing indicates that after initial film formation has occurred , residual levels need only be maintained at near the detection limit to maintain corrosion inhibition .

Summary & conclusions

Comparative testing of corrosion inhibitors was performed in a circulating hot water pilot system ( 71 ° C ) containing copper , mild steel and aluminium . The efficacy of traditional and filming chemistries was determined by metal loss over a 14-day test period .

The results clearly show the filming amines were the most effective corrosion inhibitors for all metals tested at the pH range ( 8.0-8.5 ) recommended for the protection of

Figure 4 – LPR corrosion data for MS with varying levels of filming amine

8 1

--. 7 0.9

>-

0.8 QJ a. 6 • Mild steel corrosion C

E · -

� 0.7 E

QJ 5

0.6 ro

� Filming amine residual

OD

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4 0.5 · -C

C

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Vl 4--

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0 2 4 6 8 10 12 Run time { days )

aluminium . Results using a nitrite / silicate blend show the difficulty in protecting mild steel and aluminium simultaneously ( Trial 2 ). To protect mild steel effectively , a high pH ( 9.6 ) was needed . This resulted in a corrosion rate of 378 mils / year for aluminium .

A cold-water circuit was also used to evaluate the film formation characteristics of a film-forming inhibitor blend . The data show that corrosion inhibition begins with

Run time ( hrs } Figure 5 – Extended trial of 10ppm filming amine initial dose with residual testing

the initial dose and that corrosion rates continue to improve over an eight-day period .

There are difficulties encountered when treating multi-metal systems , especially when they contain aluminium components . The results presented here show that FFA offer an effective corrosion inhibitor alternative to traditional chemistries with possibilities for use in a variety of water systems including hot , cold , open or closed . ●

32 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981