New thermogalvanic method determines the conditions which cause dezincification of admiralty brass in field service

Corrosion Science, Vol. 19, pp. 507 to 520 Pergamon Press Ltd. 1979. Printed in Great Britain

N E W THERMOGALVANIC METHOD DETERMINES THE CONDITIONS WHICH CAUSE DEZINCIFICATION OF A D M I R A L T Y BRASS IN FIELD SERVICE* V. G. ERENETA Standard Oil Company (Indiana), Materials Research & Services Division, Amoco Research Center, Naperville, Illinois 60540, U.S.A. Abstraet--A newly developed laboratory test method based on thermogalvanic currents realistically simulates the dezincification of admiraly brass in fresh or sea water. It is especially useful for studying the dezincification of brass heat exchanger tubes. The method uses an internally heated tube that is exposed to a test solution while being galvanically coupled to a relatively large colder piece of the same metal. The tube is thermally insulated in such a way that hot spots and boiling are induced on its surface. The temperature difference between the hot tube and the colder piece of metal produces a thermogalvanic action that results in current densities up to 0.16 m A c m -s. The electrode potential of the heated tube is more negative than when the tube is cold. Under these conditions, dezincification of inhibited admiralty tube occurred within 72 h in fresh water and much sooner in a 0.5% solution of sodium chloride. Under these test conditions, two types of dezincification were noted, depending on thekind of boiling and the intensity of the associated thermogalvanic current produced on the surface of the tube; localized film boiling caused a plug-type dezincification with strong evidence for the redeposition of copper, whereas localized nucleate boiling causes a layer-type dezincification with strong evidence for dissolution of the zinc. Very low water velocities, high process side temperatures, low pH or presence of a water conditioning treatment resulting in non-scaling water, high solution conductivity, and the absence of waterside corrosion inhibitors are factors which lead to dezincification in field service. INTRODUCTION DEALLOYING o f metal process e q u i p m e n t is a ~erious p r o b l e m in industry. Especially t r o u b l e s o m e is the dezincification o f heat exchanger tubes m a d e o f inhibited a d m i r a l t y brass. Loss o f zinc causes such tubes to become brittle and eventually develop holes, 1,~ thereby causing p r o d u c t or water c o n t a m i n a t i o n a n d a drastic decrease o f heat exchange capacity, d e p e n d i n g on the n u m b e r o f tubes affected. Often, a forced shutd o w n o f the h e a t exchanger to correct these associated p r o b l e m s can be costly. F u r t h e r m o r e , concern a b o u t dezincification has forced some o p e r a t o r s to lower heat exchanger temperatures, thereby greatly reducing heat exchanger capacity. Alternatively, m o r e expensive alloys are being used even t h o u g h a d m i r a l t y w o u l d suffice if only the external conditions t h a t cause dezincification were better understood. Therefore, there is a great e c o n o m i c incentive to u n d e r s t a n d specifically these conditions a n d their interaction in p r o d u c i n g dezincification. This knowledge w o u l d p r o b ably also a p p l y to the de-alloying o f cupro-nickel exchanger tubes in sea water service a n d o f M o n e l ( n i c k e l - c o p p e r alloy) reboiler tubes in m o n o - e t h a n o l a m i n e - c a r b o n dioxide acid scrubbing units. *Manuscript received 17 November 1975; revised manuscript received 1 March 1978 and 25 September 1978. 507

508

V . G . ERENE'I'A

Although inhibited admiralty brass resists dezincificationa,-5 and has totally replaced non-inhibited admiralty brass in exchanger tube application, there are many instances where inhibited admiralty exchanger tubes have dezincified in the field, in both seaand fresh-water service. Notable work has been done in the past concerning dezincification and de-alloying of binary alloys.S, 13 Much of this work dealt with the changes in the microstructure of the metal during dezincification or de-alloying. In comparison, the present investigation deals with service conditions which cause dezincification. The aim of most previous workers was to clarify the mechanism of dezincification. The present investigation is intended to provide art effective and practical method of controlling dezineifieation of inhibited admiralty brass in heat transfer service. Therefore, the test conditions in this investigation were chosen to duplicate service environment. These test conditions differed from most of the workers cited above, in that: (a) no impressed current (or impressed voltage) was used in this work. The currents measured in the tests were generated by the thermogalvanic action between an overheated area of a tube specimen and a cooler metal area concentrically surrounding the tube (and electrically coupled to the tube); (b) only fresh water or 0.5 ~ sodium chloride solution was used in the tests; (c) heat transfer was an important requirement in the tests, i.e., heat transfer occurred from an internally heated tube specimen into the test solution; (d) inhibited admiralty brass was used in the tests. No other type of copper alloy was included in this work. Lucey 6 studied the electrolytic environment theoretically required for dezincification of inhibited admiralty and concluded that the process could occur only under highly abnormal conditions. For example, with a brass corroding in a cuprous chloride/zinc chloride electrolyte, he showed that the deposition of copper from cuprous ions (Cu +) requires a potential below -- 0.41 V (SCE) whereas a brass with a single-phase alpha structure, such as admiralty brass, had a potential of -- 0.38 V in such a solution. Although cupric ions (Cu e+) can deposit as copper even at an even higher potential of -- 0.16 V, these ions could be formed only by disproportionation of the cuprous ions, a reaction prevented by the arsenic inhibitor in the brass. 7 This indicated that under normal conditions, dezincification of inhibited admiralty is highly improbable. Water conditions identified as possibly promoting dezincification include: a high temperature, strong electrolytes, such as chlorides, a low pH value, soft water (non-scaling water), and low flow velocity.1,a--6 However, nothing has been published on the specific roles of these conditions in promoting dezincification. A new thermogalvanic test method (TTM) was developed during the present work. This method realistically simulates service conditions. The TTM is based on previous work on hot spot corrosion, ~-~6 and used localized overheating to induce thermogalvanic currents on the waterside (outside) surface of an internally heated tube. The TTM, combined with other laboratory tests done during this work, correlated the external factors that causes dezincification and identified the combination of water conditions under which dezincification is most likely to occur in field service. EXPERIMENTAL METHOD Tho principal equipment comprised that of tho new TrM and a Dynamic Flow Test Assembly (DFTA).

Dezincification of admiralty brass in field service

509

Thermogalvanic test method As shown in Fig. 1, the T r M is composed of an internally heated tube which is externally coupled to a concentric cooler metal cylinder of the same material. Both the tube and the cylinder are immersed in the test solution. The thermogalvanic current generated between the overheated tube and the cylinder is measured by a technique developed by Wilhelm and Hummer. x~,18A recoi'ding potentiometer is connected across a 0.5 f~ resistor in the external circuit, and the current is obtained 15y Ohm's law. The current is generated by the thermogalvanic cell alone. No impressed voltage is used on the cell. Wrappings of fabric gauze, approximately 8 cm wide and 62 cm long wrapped around the tube, thermally insulate the tube from the bulk of the solution while allowing good electrolytic conductivity between the coupled tube and cylinder, due to the porous nature of the gauze. Localized boiling and hot spots are thus produced on the tube while the cylinder remains relatively cool. A cooling coil (Fig. 1) directly controls the temperature of the solution and the cylinder. The internally heated tube is 10 cm long and has a 2 cm outside diameter. Only the lower 8 cm of the tube is immersed in the solution. The internal cartridge heater fits snugly inside the tube. The heater has 200 W output or an equivalent output of 4 W cm -~ of immersed tube surface. In tests in which the gauze wrapping was omitted (to produce nucleate boiling instead of film boiling) a higher watt output of 357 W or a n equivalent of 7 W cm -2 was used. The temperature of the test solution is monitored by a thermocouple connected to a temperature recorder. However, the temperature of the hot tube surface was not monitored during the tests because any metal which contacts the immersed tube surface, such as a thermocouple, causes an erratic reading on the recorder potentiometer (which records the current generated by the thermogalvanic cell). This interference is due to the effect of a galvanic action between the tube and the contacting metal. However, tests with a thermocouple on the hot tube surface showed that the tube temperature remains relatively constant so long as boiling is occurring on the tube surface, for a certain cartridge heater wattage and a certain bulk solution temperature. Electrode potentials of the tube are measured with a manual potentiometer using a saturated calomel electrode. The weight loss of the tube due to thermogalvanic attack is approximated by using the data from the recording potentiometer and Faraday's law of electrolysis. The test solution was either fresh water or 0.5 % sodium chloride in distilled water. The tubes and cylinders were of admiralty brass (approximately 70% copper, 1% tin, inhibitor and balance zinc) inhibited with 0.03 % of arsenic, antimony, or phosphorus. Before each test, both the tube and the cylinder were washed with a cleanser, thoroughly rinsed with de-ionized water, and dip-rinsed in acetone.

Dynamic flow test assembly The DFTA, shown in Fig. 2, is designed to duplicate conditions of water composition, flow rate, temperature, and heat transfer to which heat exchanger tubes are exposed in field equipment. Preheated water is circulated around eight exchanger t~bes, each 123 cm long, which are enclosed in Pyrex tubes and heated internally with electrical tubular heaters. Incoming water goes through a flow controller recorder and is preheated to the desired temperature (temp. A) in the tank. It is then circulated through the Pyrex tubes at a rate controlled by a preset manual valve. Depending on that rate and the initial water temperature, the average temperature of the water increases in increments of 1-5°C (2-9°F) from one tube to the next. For example, if the initial water temperature is 49°C (120°F), designated temp. 1, the water will be heated to 56°C (133°F) or even up to 84°C (183°F), designated as temp. 8, by the time it flows through the eighth tube. Effects of various temperatures can thus be evaluated with a single test. Also, corrosion or scaling of the exchanger tubes can be observed through the Pyrex tubes while a test is in progress. At the end of each test, each specimen was inspected visually and macroscopically. If needed, the specimen was sectioned, polished, and metallographically examined. The presence of elemental copper or deposits on the affected area of the specimen was reconfirmed by qualitative chemical analysis and X-ray diffraction analysis. However, in tests with the TTM, dezincification was easily produced so that a distinct bright reddish copper colour was visually obvious on the affected metal surface. Therefore, metaliographic analysis and chemical and X-ray diffraction analyses were done as confirmatory tests only. EXPERIMENTAL

RESULTS

AND DISCUSSION

B e f o r e t h e T T M w a s d e v e l o p e d , t h e t e s t s w i t h t h e D F T A , as well as s e v e r a l b e a k e r tests, i n d i c a t e d t h a t w a t e r c o n d i t i o n s a l o n e ( r e l a t e d t o service e n v i r o n m e n t )

V. G. ERENETA

510

TABLE 1. CORROSIONTESTSON INHIBITEDADMIRALTYBRASSTUBES IN THE DFTA WXT~IONCETHROUGHCOOLINGWATER

Series

Velocity, cm s -~

. Temp. °C

Time, days

1

61

60-83

123

2

15

60-95

124

3

61

49-56

39

4

61

Cycling*

34

Results No dezincification No deposits No dezincification Light deposits No dezincifieation No deposits No dezmcification No deposits

*25 min on at 60-86°C; 10 min off at 38°C. c a n n o t p r o d u c e dezincification o f inhibited a d m i r a l t y . These tests, shown in Tables 1 a n d 3, were initially d o n e to check certain c o n d i t i o n s which were suspected o f causing dezincification in field service, as m e n t i o n e d in the reference,t, a-6 such as high temperature, low flow velocity, strong electrolytes such as chloride, low p H , a n d soft or non-scaring water (based on Langelier's S a t u r a t i o n I n d e x to o r R y z n a r ' s Index 2°. Yet, no dezincification was p r o d u c e d in the D F T A with relatively high t e m p e r a t u r e s o f 83°C (181°F) a n d 95°C (203°F), o r relatively low flow velocity o f 15 cm s -1 (0.5 fps) in c o m b i n a t i o n with relatively high t e m p e r a t u r e (95°C), even up to 124 d a y s ' test d u r a t i o n , as is shown in Table 1. T a b l e 2 shows the analysis o f the water used in the D F T A . F u r t h e r m o r e , no dezincification was evident in b e a k e r test with a 2000 p p m N a C I in distilled water at boiling t e m p e r a t u r e , o r relatively low p H TABLE 2.

WATER ANALYSIS

Total hardness, as ppm CaCOs Calcium hardness, as ppm CaCO, Magnesium hardness, as ppm CaCOs Total alkalinity, as ppm CaCOs Total dissolved solids, ppm Chlorides, as ppm CI Sulphates, as ppm SO4 pH

130 70 60 112 180 7 30 8.1

TABLE 3. CONDITIONS OF BEAKER TESTS WITH 1 0 c m LONG ROTATING TUBES OF INHIBITED ADMIRALTY BRASS

(Heated internally with cartridge heaters) Solution 2000 ppm NaCI at 43°C (I 10°F) Boiling tap water (pH 4) Boiling distilled water (pH 6) Boiling 2000 ppm NaCI

Time, days 14 30 30 30

Dezincification of admiralty brass in field service

511

(4) boiling tap water, or non-scaling (distilled) boiling water, as shown in Table 3. Therefore, it was finally concluded that a highly abnormal condition is needed to produce dezincification of inhibited admiralty in service environment. As such, the main objective of the succeeding tests was to determine what comprised this abnormal condition and to find ways of controlling the dezincification. Previous hot spot corrosion work has shown that metals covered by an insulating porous layer of scale or deposit are susceptible to corrosion. 14-16 Therefore, in additional beaker tests, a layer of deposit was simulated by wrapping the middle section of the internally heated 10 cm long tube with fabric gauze. This produced an effect similar to a porous layer of deposit. With a wrapping 1.3 cm wide, no effect was noticed after an immersion test in boiling 0.5 70 solution of sodium chloride. However, when the width of the wrapping was increased to 6.4 cm, appreciable pitting and traces of dezincification developed underneath the wrapping. Evidently, the gauze created sufficient overheating to induce thermogalvanic currents between the overheated (covered) area and the relatively cooler (uncovered) sections of the tube. Except for this effect, as shown later, the gauze provided no other significant effects such as concentration or occluded cell effects. The result of the initial thermogalvanic test led to the development of the TTM, which permitted the study of dezincification phenomena under conditions which closely simulated service environment. In the TTM, the hot spot area is physically separated from the colder metal area that normally adjoins or surrounds a hot spot. The hot spot area is represented, by the hot (internally heated) tube while the colder adjoining area is represented by the concentric metal cylinder, which is externally connected to the tube (Fig. 1). This method of physical separation, while maintaining external contact or coupling, was necessary in order to facilitate the measurement of the current generated between the 'hot spot' area and the surrounding cooler area. When uncoupled, the arrangement also allows the measurement of the static potential of the hot or cold tube.

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The results of the tests done in this work, especially those with the TTM, indicate that a combination of three conditions is needed to produce dezincification of inhibited admiralty brass under test conditions which simulate a heat transfer surface in aqueous environment (such as in heat exchangers). These three conditions, which should be present concurrently, are :" 1. Localized waterside boiling or overheating, usually due to stagnant water or low water flow rates of approximately 9 cm s -1 (0.3 fps) or less, and very hot process side inlet temperatures, such as 204°C (400°F) or higher. The localized overheating generates hot spots and corresponding thermogalvanic currents, whereby the hot spots are severely attacked. 2. Soft or non-scaling water, one that has a low pH or low hardness, or has been stabilized with polyphosphates, phosphonates, organic phosphates, lignin, tannin, or other water conditioning compounds which inhibit scale formation, even under overheated or boiling conditions. This type of water allows the thermogalvanic action to proceed unabated. 3. Absence of an effective aqueous corrosion inhibitor. Otherwise, the thermogalvanic attack will be stifled. Typical T T M results obtained under varied test conditions are summarized in Table 4. Whereas dezincification occurred in both the soft water anci 0.5~o NaCI solution, no dezincification was evident in either the slightly hard water or the soft water treated with a Cr-Zn inhibitor. Previously, it was shown that in the absence of thermogalvanic action, no dezincification occurs in soft, low pH water or chloride solution even at boiling temperature. An explanation of this phenomenon is as follows: in a soft or non-scaling water (even up to localized boiling temperatures) the deposition of calcium carbonate or any impermeable water deposit will not occur on the locally overheated metal areas; hence, the overheated area is vulnerable to any prevailing electrochemical reaction. For example, when localized boiling or overheating is present in the waterside of an admiralty heat exchanger tube, an electrochemical reaction in the form of a thermogalvanic cell (with associated thermogalvanic currents) occurs between the overheated areas (hot spots) and the nonoverheated area in this tube. The hot spots in this case are the anodes of the thermogalvanic cell and are corroded, while the cooler area is the cathode and is unattacked. If the static potential of hot spots can be measured, it is evidently more negative compared with that of a cooler area as shown in Table 4, Tests 1-4, in which the potential of an uncoupled internally heated tube was more negative (anodic) compared with the potential when the same tube was cold. This potential difference is responsible for the consequent thermogalvanic current that is generated. For example, as shown in Test 1, the uncoupled potential of the uncoupled tube shifted from - 5 2 mV to-- 170 mV when the tube was heated. With this more negative hot tube potential, a corresponding thermogalvanic current of 0.08 mA cm -~ (74.3 mA ft -2) resulted when the hot tube was coupled with the non-internally-heated concentric admiralty cylinder. At this stage, if deposits form (as in Test 3) or if a corrosion inhibitor is present (as in Test 4), the thermogalvanic cell and associated thermogalvanic current will be stifled (or minimized), thereby controlling thermogalvanic corrosion and preventing dezincification. As shown in Tests 3 and 4 of Table 4, at current densities below 0.017 mA cm -2 (15 mA ft-2), dezincification did not occur with the TTM.

Dezincification of admiralty brass in field service

515

To confirm the inhibiting effect of water scaling .19-2x on dezincification, the pH of the soft or non-scaling water used in Test 1 was increased to 8.6 to enhance its scaling tendency. 21 As expected, no dezincification was produced with t3ae TTM and careful examination of the tube specimen showed no elemental copper. Based on the test results, the area where dezincification is likely to occur in a heat exchanger is shown by the heavy lines in Fig. 3 (at the end of the uppermost tube or tubes of the exchanger) which is the first tube area to contact the hot incoming process fluid (shell side). This is an area where localized overheating can readily form if conditions are right. The corresponding waterside tube area can develop localized overheating if the process temperature is hot enough and if the waterside flow velocity is quite low. A thermogalvanic cell (and associated thermogalvanic currents) will then result on the waterside of the tube between the overheated tube area and the adjacent 'cooler' area. If mitigating conditions previously mentioned are absent and

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FIG. 2. Dynamic flow test assembly (DFTA). *Defined as the precipitation and associated deposition of dissolved water solids such as carbonares. Water scaling can form an adherent, and protective scale, as in the case of calcium carbonate. This scaling is a function of water pH, alkalinity, concentration of calcium, magnesium, total dissolved solids and temperature.

516

V.G. ERENETA

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FIG. 3. Typical location of localized overheating on the waterside of a heat exchanger. if sufficient temperature difference exists, i.e., sufficient driving potential difference (manifested as current flow) between hot spots and the adjacent 'cooler' area, and if the ratio between the 'cooler' tube area and the hot spots area is great enough to produce high current densities, accelerated thermogalvanic corrosion and subsequent dezincification will occur, as shown by the TTM. The T T M also showed that either redeposition or selective dissolution type of dezincification can occur, depending on conditions, such as the type of boiling and the corresponding degree of overheating or superheat on the metal surface. In turn, the degree of overheating determines the intensity of the thermogalvanic action and associated thermogalvanic current. Localized film boiling, *z2 which cause considerable overheating and results in higher thermogalvanic current densities, causes plugtype dezincification with strong evidence of redeposition of copper, as shown in Fig. 4, where dendritic growth of copper is evident even up to four gauze layers from the dezincified tube surface. Test 1 of Table 4 is an example of the thermogalvanic data which resulted in this type of dezincification. However, localized nucleate boiling,1"22 which minimizes the presence of overheating and results in lower thermogalvanic current densities, causes a layer-type dezincification with strong evidence for dissolution of zinc, as shown by the results in Test 2 of Table 4. After 29 h during Test 2, a selective dissolution type of dezincification was evident, as indicatedby auniformwhite coating of zinc oxide around the tube specimen. When the test was stopped after 307 h, a porous layer of elemental copper was found underneath the zinc oxide layer. The zinc oxide was carefully removed in order not to disturb the underlying copper layer. Thickness measurements showed the zinc oxide layer was 0.03 to 0.05 mm thick and the copper layer was 0.04 to 0.07 mm thick. Both visual and microscopic examination dearly showed the presence of two distinct layers. Chemical and X-ray diffraction analyses and electron microprobe examination identified the two layers as zinc oxide and elemental copper. Based on this configuration, it was obvious that the zinc (later converted to zinc oxide) has selectively dissolved leaving behind a layer of porous copper. Evidently, as shown in Table 4, under these test conditions, a *Description of film boiling--a vapour blanket is present over the heated surface, at high heat flux, resulting in considerable superheating, decreased heat transfer coefficient,and increased temperature differencebetween the metal surface and the liquid. 1"Descriptionof nucleate boiling--numerous small bubbles rise from the heated surface, agitating the liquid and creating a condition favourable for heat transfer. This minimizesthe temperature difference b e t w e e n the metal surface and the liquid.

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FIG. 5. The non-effect of gauze wrapping on the tube specimen in the absence of thermogalvanic action. Item 1: after 3 weeks exposure with gauze wrapping in the absence of thermogalvanic action. Item 2: new tube. Item 3: excessive tube attack underneath the gauze wrapping, in the presence of thermogalvanic action. Item 4: gauze wrapping after a thermogaivanic test, showing specks of elemental copper on the gauze.

Dezincification of admiralty brass in field service

519

higher thermogalvanic current density ranging from 0.08 to 0.16 mA cm -2 (74149 mA ft -2) is needed to produce redeposition of copper, while a lower thermogalvanic current density ranging from 0.017 to 0.022 m A c m -2 (15.7-20J mA ft -2) produces selective dissolution of zinc. As previously mentioned, below 0.017 mA cm -2 . (15.7 mA ft-~), no dezincification was produced under these test conditions. A confirmatory test was done to be sure that the dezincification and pitting produced in TTM tests were caused by thermogalvanic currents resulting from the overheating of the affected metal area (resulting from the gauze wrap), rather than due to a concentration cell, differential oxygen concentration effects, or differential potential effects produced underneath the gauze. An autoclave test at 121°F (250°F) with the 0.5 70 NaCI solution was done with a gauze-wrapped admiralty tube specimen, galvanically connected to a concentric metal cylinder of admiralty. This is similar to the TTM set-up. However, the tube specimen was not internally heated; i.e. there was no temperature difference between the gauze-covered tube area versus the concentric cylinder coupled to the tube. After three weeks' test (504 h), no attack was evident underneath the gauze wrapping. The wrapped tube area looked as good as new, as shown in Fig. 5, Items 1 and 2. The tube area not covered by the gauze became oxidized. In comparison, Item 3 shows excessive tube attack underneath the gauze wrapping in the presence of thermogalvanic action after only 24 h exposure. Elemental copper is shown adhering to the gauze, right next to the tube surface. Item 4 shows a part of a gauze wrapping after a thermogalvanic test, showing specks of elemental copper on the gauze, up to three gauze layers away from the tube surface. All these conclusively showed that concentration cell or any occluded cell effect or oxygen concentration effects did not cause the dezincification produced in this work. CONCLUSIONS The three conditions which have to be present concurrently to produce dezincification of inhibited admiralty in the waterside of heat exchangers are: (1) localized boiling or overheating which results in strong thermogalvanic action (producing sufficient thermogalvanic currents) between overheated spots and adjoining colder areas; (2) non-scaling water even at boiling temperatures; and (3) the absence of an effective waterside inhibitor. Water p H plays a role in that it affects the scaling tendency of the water. Low pH tends to make the water non-scaling while higher pH enhances scaling, thereby providing corrosion protection, if the scale is adherent and impermeable. The role of low water flow velocities and high water and process side temperatures is in enhancing localized boiling and overheating, thereby enhancing the thermogalvanic action. Dezincification of inhibited admiralty exchanger tubes can be prevented by eliminating any one of these three conditions. Knowing the spedfic role of each of the conditions as explained above, it was possible to correct dezincification problems at two petroleum refineries. In both cases, partially softened water was being used in the cooling water system to control waterside fouling. This resulted in a relatively non-scaling water. To control the dezincification problem, better pH control was recommended in order to maintain a pH slightly above 7, instead of p H swings that ranged between 5.8 and 6.8. This was designed to produce slight scaling in locally overheated tube areas and form a protective scale on these hot spots, thereby stifling any thermogalvanic action and associated dezincifica-

520

V . G . ERENETA

tion. Although the cooling water was treated with a chromate-zincinhibitor, frequen, loss of inhibition occurred due to the presence of process leaks and associated hydrogen sulphide contamination. These made the inhibitor ineffective. Otherwise, the presence of the waterside inhibitor would have controlled the thermogalvanic action (and dezincification) as illustrated in Table 4, Test 4. The elimination of localized overheating and hot spots would have also solved the dezincification problem in both refineries. However, this remedy was considered impractical at the time because it involved the reduction of process inlet temperatures (and a corresponding upset in the process side), or an increased water flow and increased water pumping capacity, which involved considerable cost. The TTM and the explanation which it provides on the specific roles of certain conditions in producing dezincification will probably help also in controlling dealloying problems in other types of metal, for example, that of cupro-nickel heat exchanger tubes in sea water service or Monel (nickel-copper alloy) reboiler tubes in mono-ethanolamine-carbon dioxide (MEA-CO2) acid gas scrubbers. Acknowledgement--Appreciation is extended to Standard Oil Company (Indiana) for allowing this work to be published. Appreciation is also expressed to A. S. Couper and Profess.or E. J. Wilhelm (University of Notre Dame, Indiana) for their advice and to J. A. Homyak and J. Van Hess for their aSSistance. REFERENCES 1. H. H. UHLIG,Corrosion and Corrosion Control, pp. 289-290, Wiley, New York (1963). 2. F. L. LAQUE and H. R. CoPsoN, Corrosion Resistance of Metals and Alloys, p. 17, Reinhold, New York (1963). 3. BRIDGEPORTBRASSCOMPANY, Condenser and Heat Exchanger Tube Handbook, pp. 99-100 (1964). 4. CHASEBRASSand COPPER COMPA~,r:, Condenser and Heat Exchanger Tube Manual, Chase BraSS Publication D-10, p. 27. 5. SCOVILLMANUFACTURINGCOMPANY,Heat Exchanger Tube Manual (3rd Edn), pp. 17-18 (1957). 6. C. W. STILLWELLand E. A. Tt.atNIPSEED, Ind. Engng Chem. 26, 740 (1934). 7. V. F. LUCEY,Br. Corros. J. 1, 53 (1965). 8. H. W. PICKERIN6 and C. WAGNER,2". electrochem. Soe. 114, 698 (1967). 9. H. W. PICK~gL~O,J. electrochem. Soc. 115, 143 (1968). 10. H. W. PICKERINOand P. J. BYmCE,2". electrochem. Soc. 118, 209 (1971). 11. R. H. I-IEtDERS~ACH,Corrosion 26, 445 (1970). 12. R. H. I-IBXDERSaACHand E. D. VERII'aC,JR., Corrosion 28, 397 (1972). 13. E. E. LmqOEh~OGERand B. G. CALLAOHAN,Corrosion 28, 245 (1972). 14. C. BgECKON and P. T. GILBERT, First International Congress on Metallic Corrosion, London, p. 624 (1961). 15. R. S. BeM and H. S. CAMPBELL,First International Congress on Metallic Corrosion, London, p. 630 (1961). 16. R. J. BODEN, Second International Congress of Metallic Corrosion, London, p. 771 (1963). 17. C. W. HUMMERJR. and E. J. WILHELM(adviser), M.S. Thesis, University of Notre Dame, South Bend, Indiana, U.S.A. (1960). 18. E. J. W~rmLM and V. G. EgZNL~r^, Corros. Sci..3, 1005 (1973). 19. W. F. LANGELIER,J. Am. Wat. Wks Ass. 28, 1500 (1936). 20. J. S. RYZNAR,J. Am. Wat. Wks Ass. 36, 472 (1944). 21. BeTZ LAeORATO~eS, Betz Handbook of Industrial Water Conditioning, p. 240 and 259 (1962). 22. C. G. BgowN and ASSOCIATES,UnR Operations, p. 453--454, Wiley, New York (1950).