LABORATORY RESULTS

 

Multi-metal Electrolysis Erosion Tests Using Variably-Inhibited Coolant Solutions

© 2010 Applied Chemical Specialties, Inc.

ABSTRACT:

The purpose of this test is to determine the differential weight loss of various metal corrosion coupons due to electrolysis effects in varied coolant mixtures using simulated engine conditions and simulated electrolytic low-voltage current. 

ASTM has NOT established a standardized test method to be used for electrolysis testing of metals exposed to coolant.  Therefore, the primary focus of this test is not to provide exact quantification of weight loss, but rather to provide comparative insight into the relative effectiveness of a new cooling system corrosion inhibitor product formula.  As such, there will be two controls in this analysis.  The first will be coolant consisting of straight water.  The second will be coolant consisting of a mixture of 50% water and 50% antifreeze.  Both of these controls will be tested both with and without the cooling system corrosion inhibitor product added.  Relative rates of weight loss of various different metal corrosion coupons will be compared as a means of establishing relative effectiveness of the product in reduction of damage due to electrolysis.  For testing purposes, a voltage of 150 mV will be used in order to simulate electrolysis caused by galvanic action between dissimilar metals.  It should be noted that this is higher than that which is encountered in most in-field cooling system applications, unless a component was not grounded properly, or unless there was stray current from an electrical component. 

The mechanism by which NO-ROSION provides electrolysis protection involves formation of resilient, passive surface films on metal surfaces inside the cooling system.  This is achieved via a proprietary blend of organics, tolytriazole, mercaptobenzothiazole, and nitrite ingredients contained the product formula. Surface films provide resistance to the stripping of electrons, and therefore reduction of weight-loss associated with erosion which is directly attributable to electrolysis.  This test will provide actual numeric data to support this theory with actual simulated cooling system weight loss data from different metals.

For the purposes of the test, the simulated cooling system as described in ASTM Test Method D2570 will be run for a period of 1 week in order to create temperature and flow sufficient to allow the proprietary blend of ingredients to properly passivate the corrosion coupon sample specimens.  Only after this passivation period has taken place will the electrolytic current be applied.

Weight loss data from a 7 week test period will be used to calculate an extrapolated annual Erosion Rate which is directly attributable to electrolysis.  The standard of measure for the Erosion Rate will be recorded in milligrams per year (mpy), thus allowing benchmarking of the various control and test variables.

MATERIALS:

(1)  All testing equipment and apparatus as described in detail in the ASTM D2570 procedure.

(2)  Corrosion coupon test specimens (aluminum, copper, brass, and iron) as supplied by Midland Scientific Company.

(3)  Prestone antifreeze as supplied by local auto parts store. (Note:  Traditional blend of antifreeze was used, which utilizes silicate inhibitors)

(4)  NO-ROSION Cooling System Corrosion Inhibitor as supplied by Applied Chemical Specialties.

(5)  High ionic strength corrosive tap water with the following properties:

 

pH =                                7.0

Calcium (as CaCO3) mg/l =           300

Magnesium (as CaCO3) mg/l =         100

Chloride (as Cl) mg/l =             500

Sulfate (as So4) mg/l =             500

Silica (as SiO2) mg/l =             20

Total Alkalinity (as CaCO3) mg/l =  20

Conductivity in micromohs/cm =      1710

Langelier Saturation Index =        -0.7

Ryzner Stability Index =             8.4

(6)  Sodium nitrite test kit as supplied by LaMotte.

(7)  Conductivity meter as supplied by LaMotte.

(8) Specially devised sample reservoir, similar to that described in ASTM Test Method D2570 except that the metal test coupons (aluminum, copper, brass, and iron) are mounted to an iron sample holder such that one entire side of each coupon is in contact with the metal sample holder, through which the low voltage current is being supplied.

PROCEDURE:

(1)  The test apparatus was assembled as described in ASTM Test Method D2570.  The sample reservoir used in this test varied from that described in ASTM Test Method D2570 as described above. 

(2)  Each of the corrosion coupon sample specimens to be used in all tests was pre-weighed in order to determine an initial weight in milligrams. 

(3)  For Test 1, the system was filled with a mix of 50.0% antifreeze and 50.0% tap water.  The pump was started, and checked to ensure that the coolant mixture was circulating.  The unit was run for 5 minutes in order to ensure that the system was operating properly and to remove trapped air.  Any leaks were detected and mechanical means of correction were taken.

(4)  With the system shut down, the corrosion coupon metal specimens were allowed to remain in the coolant mixture for 24 hours under static conditions, no flow and no heat.

(5)  Heat was applied in order to bring the system up to test temperature of 190 degrees F (88 degrees C).  The system was pressurized to 15 psi (103 kPa).

(6)  The system was operated continuously at constant temperature, pressure, and flow of 25 gal/min for a period of 168 hours.   Twice during this period the system was taken off line for 8 hours each time.

(7)  During this initial 168 hour run period, the corrosion coupon sample specimens were allowed to form passive surface films WITHOUT the presence of electrolytic current.

(8)  At the conclusion of the initial run period, the system was shut down for 3 days and allowed to sit at room temperature and barometric pressure, with zero flow.

(9)  At the conclusion of the 3 day period, the system was again brought up to the same  operating temperature, pressure, and flow, and this time the electrolytic current was brought up to 150 mV.  The system was run for a period of 1064 hours, except for two 8 hour shutdowns per week.  The interval between the shutdowns was 3 days, with shutdowns beginning at the same time on Thursdays and startups beginning at the same time on Mondays.  This schedule was followed at 152 net hours of operation per week, until the 1064 hours of operation had been completed.

(10)  The system was shut down, and the samples removed, dried, and cleaned in accordance with the procedures in ASTM Test Method D1384.  The system was then flushed and rinsed well with tap water in preparation of the next test.

(11) Procedures 1-9 were repeated for Test 2, with 48.5% antifreeze, 48.5% tap water, 3.0% inhibitor.  

(12) Procedures 1-9 were repeated for Test 3, with 100.0% tap water.

(13) Procedures 1-9 were repeated for Test 4, with 97.0% tap water, 3% inhibitor.

(14)  At the completion of all tests, the corrosion coupon sample specimens were again weighed in order to determine a final weight.

(15)  The weight losses were calculated for each of the corrosion coupon sample specimens from each test, and the eight week test period weight loss was extrapolated to 52 weeks in order to calculate a relative erosion rate in milligrams per year (mpy). 

RESULTS:

TEST 1:  50.0% Antifreeze, 50.0% Tap Water, 150 mV current

                                                                        RELATIVE

                  INITIAL           FINAL             WEIGHT            EROSION

METAL             WEIGHT (mg)       WEIGHT (mg)       LOSS (mg)         RATE (mpy)

Aluminum          3906.0            3892.9            13.1              85.2

Copper            4412.8            4406.4            6.4               41.6

Brass             4893.4            4888.1            5.3               34.5       

Iron              4598.7            4596.1            2.6               16.9

TEST 2:  48.5% Antifreeze, 48.5% Tap Water, 3.0% Inhibitor, 150 mV current

                                                                        RELATIVE

                  INITIAL           FINAL             WEIGHT            EROSION

METAL             WEIGHT (mg)       WEIGHT (mg)       LOSS (mg)         RATE (mpy)

Aluminum          3878.4            3873.9            4.5               29.3

Copper            4349.1            4347.2            1.9               12.3

Brass             4911.1            4909.5            1.6               10.4

Iron              4635.4            4634.4            1.0               6.5

TEST 3:  100.0% Tap Water, 150 mV current

                                                                        RELATIVE

                  INITIAL           FINAL             WEIGHT            EROSION

METAL             WEIGHT (mg)       WEIGHT (mg)       LOSS (mg)         RATE (mpy)

 

Aluminum          3889.0            3851.3            37.7              245.0

Copper            4456.4            4440.7            15.7              102.0

Brass             4887.3            4874.3            13.0              84.5 

Iron              4636.8            4627.9            8.9               57.9

TEST 4:  97.0% Tap Water, 3.0% Inhibitor, 150 mV current

                                                                        RELATIVE

                  INITIAL           FINAL             WEIGHT            EROSION

METAL             WEIGHT (mg)       WEIGHT (mg)       LOSS (mg)         RATE (mpy)

 

Aluminum          3940.2            3935.4            4.8               31.2

Copper            4387.5            4385.3            2.2               14.3

Brass             4943.9            4942.1            1.8               11.7

Iron              4537.8            4536.6            1.2               7.8

CONCLUSION:

In comparing the relative erosion rates of each of the corrosion coupon sample specimens from each of the tests, it is clear that the NO-ROSION proprietary blend contributed significantly to reduced amounts of electrolytic weight loss. 

The test results indicate that in a cooling system filled with a 50/50 mixture of tap water and antifreeze, the relative erosion rate of aluminum due to electrolysis is reduced by nearly 66%.  This suggests that the effective lifespan of aluminum cooling system components can be lengthened by nearly 300% by the addition of 3% NO-ROSION to the coolant solution.  In a typical 16 quart cooling system, this represents approximately 1 pint of product.  Similar results were observed for cooling system components consisting of copper, brass, and iron.  The tests results suggest that the relative effective lifespan of copper components should be lengthened by nearly 340%, brass by 330%, and iron by 260%. 

The test results also indicate that NO-ROSION contributes even more significantly to electrolysis reduction in cooling systems containing straight water as coolant.  In a system containing straight water as coolant, plus 3% NO-ROSION, the relative erosion rate of aluminum due to electrolysis is reduced by 87%.  This suggests that the effective lifespan of aluminum cooling system components can be lengthened by nearly 800% by the addition of 3% NO-ROSION to the coolant solution.  Again, in a typical 16 quart cooling system, this represents approximately 1 pint of product.  Similar results were observed for cooling system components consisting of copper, brass, and iron.  The tests results suggest that the relative effective lifespan of copper components should be lengthened by nearly 720%, brass by 720%, and iron by 740%.

It should be reiterated that the amount of current used in these tests is higher than that which is actually encountered in most auto and truck cooling systems.   The 150 mV test voltage was used as a means of reducing the length of test time necessary in order to simulate long-term eletrolytic weight loss of the metals tested.  As such, an artificially accelerated electrolysis process was created for the purpose of achieving relative rates of erosion which can be benchmarked against one another.  Accordingly, the absolute values of the test results achieved should not be interpreted, but rather their values relative to one another for comparative purposes only.  All research indicates the comparative methodology used in this study is accurate insofar as it allows differential erosion rates to be compared for different coolant solutions.  Research that has been referenced as a means of documenting the analytical efficacy and accuracy of the methodology utilized for this comparative analysis suggests that it is sound based upon previously documented studies.*

*REFERENCES:

“Standard Test Method for Simulated Service Corrosion Testing of Engine Coolants:  Designation D2570 under the jurisdiction of ASTM Committee D-15 on Engine Coolants,” American Society for Testing and Materials, Philadelphia, PA., 1995.

M. Pourbaix, “Atlas of Electrochemical Equilibria in Aqueous Solutions,” National Association of Corrosion Engineers, Houston, TX, 2nd edition, 1974.

M.S. Vukasovich and F.J. Sullivan, “Inhibitors and Coolant Corrosivity,” 2nd International Symposium on Engine Coolants and Their Testing, American Society for Testing and Materials, Philadelphia, PA, 1984.

J. Augustynski, “Passivity of Metals,” R.P. Frankenthal and J. Druger, Electrochemical Society, Princeton, NJ, 1978.

J. Kruger, G.G. Long, M. Kuriyama, A.I. Goldman, “Passivity of Metals and Semi-Conductors,” M. Frement, (ed.), Elsevier Science Publishers, B.V. Amersterdam, 1983.

Model PMO Test Kit, La Motte Chemical Products Company, Chestertown, MD.

A. Al-Borno, M. Islam, R. Khraishi, “Multicomponent Corrosion Inhibitor System for Recirculating Cooling Water Applications: Based on Nitrite, Molybdate, and Inorganic Phosphates,” Kuwait Institute for Scientific Research, Safat, Kuwait, 1989.

 
 

© Copyright 2010 Applied Chemical Specialties, Inc.