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| Home >> Services >> Potential Adjustment Protection |
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| Normally passive metals can suffer from pitting and crevice corrosion when exposed to oxidizing chloride (halide) environments. Through the application of a direct current, the structure potential can be shifted back to the passive region from the transpassive region. This method is used extensively on stainless steel bleach washer facilities in the pulp and paper industry. Stainless steel flue gas scrubbers and brine evaporators have also been protected using this method. In effect, this technique upgrades the corrosion resistance of passive metals making their corrosion resistance comparable to higher grade alloys. |
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| Typical polarization behaviour for stainless steel in an oxidizing chlorine environment |
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- Bleach washer drums and valves
- Stainless steel Flue Gas Desulfurization (FGD) scrubbers and associated equipment
- Municipal stainless steel biological rotating contactors
- Salt concentrators/evaporators
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Author : J.I. Munro / D. Singbeil
Date : May-90
Notes : CPPA Conference |
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| More than 100 potential adjustment protection (PAP) systems for bleach plant washers have been installed over the past decade. Long-term monitoring data from these systems shows that electrochemical protection can more than double the lifetime of a bleach washer, sufficient to pay back the capital and operating costs in one year. |
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Author : W.W. Shim / E.R. Dille
Date : Mar-98
Notes : NACE Corrosion 98 |
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| Austenitic chromium-nickel-molybdenum-iron alloys (904L, 316L, 317L, etc.) used to construct Flue Gas Desulfurization (FGD) scrubbers and associated equipment in coal fired generating stations can experience localized corrosion. The problem may be alleviated by using more costly materials such as higher grades of stainless steel or high nickel alloys. An alternative and more cost-effective method of prolonging equipment service life is the use of potential adjustment protection, an electrochemical protection system (EP). Weight-loss coupon results in environments similar to FGD scrubbers have shown that the use of electrochemical protection prolongs the life of stainless steels in oxidizing acid-chloride environments by an average of 3 to 5 times. This paper discusses an EP system that was recently supplied to an electric power utility company to protect a 316L thin metallic lined (wallpapered) FGD scrubber reaction tank. Acidic effluent from the absorber section of the scrubber is piped into this reaction tank for limestone neutralization and hence formation of calcium sulfate. Inspection of the protected reaction tank after one year of operation as well as in-situ coupon test results indicated that the EP system was very effective in mitigating localized corrosion of the scrubber reaction tank. The results are presented in this paper. |
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Author : E.R. Dille / K. Frizzell / W.W. Shim
Date : Aug-99
Notes : MEGA Symposium |
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| At Owensboro Municipal Utilities, Elmer Smith Station, localized pitting corrosion had penetrated the 1/2-inch walls of the flue gas desulfurization (FGD) stainless steel 317LMN reaction tanks after two years of operation. In addition, thiosulfate pitting, crevice corrosion, and oxygen concentration cell corrosion have been found. Photographs of the corrosion and analytical data of the corrosive environment in the reaction tank will be presented. An electrochemical protection (EP) system has been installed to control all the previously listed forms of corrosion. Actual operating data will be presented. Significant cost savings are realized over conventional corrosion control techniques. |
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Author : W.W. Shim / E.R. Dille
Date : Mar-00
Notes : NACE Corrosion 2000 |
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| At three flue gas desulfurization (FGD) systems, localized pitting corrosion, thiosulfate pitting, and crevice corrosion has occurred on the inner surfaces of fourteen stainless steel FGD reaction tanks. An electrochemical protection (EP) system is installed on each of these fourteen FGD reaction tanks to control all the previously listed forms of corrosion. Corrosion data shows that the previous corrosion is under control. Significant cost savings are realized over conventional corrosion control techniques. |
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Author : E.R. Dille / K. Frizzell / W.W. Shim
Date : Aug-04
Notes : NACE AIRPOL Symposium (Washington, DC) |
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| A proven technique for the construction of low cost flue gas desulfurization (FGD) scrubbers and associated tanks is presented. Since 1981, electrochemical Potential Adjustment Protection (PAP) systems have been protecting stainless steel against the corrosive FGD environment. To date 14 FGD scrubber reaction tanks with PAP systems, fabricated of various low alloy stainless steels, have resisted corrosion where higher chromium/nickel/molybdenum alloys would have been mandatory. Performance data and cost data will be presented to allow designers of FGD systems to specify the proven PAP technique. |
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