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Long Term Testing of Aluminium Sacrificial Anode
For Cathodic Protection Application in Seawater

LONG TERM ANODE PERFORMANCE TEST
REFERENCE: DNV RP B401 APPENDIX B
Introduction
MPE commenced the long-term testing of sacrificial anode materials in according to DNV RP B401 Appendix B on 9th January 2004 and completed on 7th January 2005 (12 months testing duration). The test was conducted in MPE laboratory, verified and certified by ThirdParty Inspection Company, ABS Consulting Sdn Bhd, hereinafter referred to as “ABS”. Five different batches/melts of MPE III anode specification were taken from normal production during anode manufacturing. Result of MPE III anode test specimens is shown in this report.
Test Condition

TEST SPECIMENS

2 samples representing each batch of MPE III specification were machined to diameter of 30mm and length of 80mm. Samples were die-stamped with laboratory identification as per “Table 1”. All test specimens were stamped by ABS.

TEST SPECIMENS IDENTIFICATION

Table 1: Laboratory Identification No.

No. Batch No./Melt No. Lab. Identification by die-stamping
1 A030559A 1A
2 A030559B 1B
3 A030560A 2A
4A030560B2B
5A030561A3A
6A030561B3B
7A030562A4A
8A030562B4B
9A030563A5A
10 A030563B5B
Test Environments

The test set-up and test-cell are shown in figure 1. The testing environment was clean natural seawater with salinity of approximately 34 ppK and at a temperature of 20º C + 2º C. Temperature and salinity were recorded weekly, shows in Table 2 . The seawater in the cell was continuously exchanged at a rate of approximately 2 liter/minute and continuously purged with air.

Table 2 : Temperature and Salinity Data

Week 1 2 3 4 5 6 7 8 9 10 11 12 13

Temp.
(º C)

 20 21 20 20 20 23 18 19 18 18 20 20 18
Salinity
(ppK)
 32 32 32 32 32 32 32 32 32 35 35 33 35

Week 14 15 16 17 18 19 20 21 22 23 24 25 26

Temp.
(º C)

 20 18 18 18 20 18 21 20 21 20 21 21 21
Salinity
(ppK)
 36 32 34 34 33 33 35 34 37 32 34 37 36

Week 27 28 29 30 31 32 33 34 35 36 37 38 39

Temp.
(º C)

 21 21 21 21 21 18 20 19 18 19 18 19 20
Salinity
(ppK)
 36 36 36 35 33 35 35 35 38 37 35 36 35

Week 40 41 42 43 44 45 46 47 48 49 50 51 52

Temp.
(º C)

 18 22 20 21 20 21 19 20 20 20 19 20 19
Salinity
(ppK)
 35 34 32 33 33 33 33 33 30 31 32 35 36

Test Procedure
APPARATUS: The following apparatus was used:

i. The container with steel pipe as cathode is filled with natural seawater.
ii. Titanium rod.
iii. Constant power supply : DC constant power supply with variable resistance and DC milliammeter and attached with electronic totalizer.
iv. Silver/Silver Chloride (Ag/AgCl) to measure potential reading.
v. Voltmeter

CIRCUIT: The circuit was arranged as shown in Figure 1.



TEST SPECIMENS SET-UP

Preparation - A hole was drilled and threaded on one of the ends for connection to a support titanium rod. The support rods (titanium rod) of the test specimen that were exposed to the test solution were coated with an epoxy resin. The test specimens were rinse thoroughly first in tap water and then dried with acetone. Test specimens were weighed and recorded to the nearest 0.1mg on an analytical balance.

The test was performed as a “free running test” where the test specimens and cathode were connected to a 10-ohm precision resistance. During the initial one-week (7days) continuous run, the applied current flow was established based on anodic current density of 1 mA/cm2. Thereafter the current density was reduced to 0.5 mA/cm2 for the remaining duration of the test.


Calculation of Applied Current Flow:

Surface area of sample exposed = Pi(DL) + 2(Pi)2
= Pi(3) (8)cm2 + 2(Pi)(1.5)2
= 75.40 cm2 + 14.14 cm2
= 89.5 cm2

For the first one week, Current flow = Current Density x Surface area.
= 1 mA/cm2 x 89.5 cm2
= 89.5 mA

After one week test until completion = 0.5 mA/cm2 x 89.5 cm2
= 44.75 mA

A totalizer measured the total applied current that passed through the system. Anode weight loss was determined at the end of the 12 months test when the samples were removed, cleaned and weighed. Anode current capacities are then determined from knowledge of the total charge passed through the system and the weight loss of the anode sample. Anode potential reading was measured using Ag/AgCl reference electrode.

The anodic current density was calculated from measurement of the voltage drop across the 10- ohm circuit resistance. Measurement of both current and anode potential were collected once per week.

After completion of the full test period, the test specimens were cleaned for 10 minutes at 80ºC in a solution containing chromium trioxide (CrO3) and 30mL concentrated phosphoric acid (H3 PO4) mixed with 1liter tap water. The specimens were then rinsed thoroughly with tap water and dried with acetone.

(Note : Cr (VI) waste may be reduced to Cr (III) with sodium bisulfate ( NaHSO3). Dissolve 3.75g sodium disulfate per gram of Cr (VI) in the solution and mix for 1h.)

Final weight of test specimens were obtained and recorded.

CHEMICAL COMPOSITION ANALYSIS

Table 3 : Chemical Analysis of Test Specimens
Chemical Composition Percentage by weight (%)
Batch No Fe Si Cu Zn In Ti Others Al
A030559
 0.077 0.047 0.001 4.284 0.016 0.005 0.004 95.566
A030560
0.084 0.051 0.001 4.286 0.016 0.006 0.004 95.552
A030561
0.078 0.050 0.001 4.251 0.016 0.005 0.004 95.595
A030562
 0.083 0.047 0.001 4.295 0.016 0.005 0.004 95.549
A030563
0.085 0.045 0.001 4.127 0.016 0.005 0.004 95.717


Table 4 : Chemical Composition Specification

Chemical Composition Percentage by weight (%)
  Fe Si Cu Zn In Ti Others Al
MPE III .10 max .10 max .006 max 2.0-6.0 .01-.05 .025 max .02 max remainder

DENSITY TEST

Calculation of Density ? Density (g/cm3) = x (g)/ y (cm3)
Where, x = weight of sample & y = the volume of water displaced

Conversation ? 1 ml = 1 cm3 (Water density = 1.00 g/ml, therefore 1g = 1 ml)

Test specimen batch no. A030559 A030560 A030561 A030562 A030563
Sample weight (g)
10.704
7.941
9.798
10.084
9.283
Water displacement (g)
3.953
2.891
3.543
3.709
3.333
Density (g/ cm3 )
2.708
2.747
2.765
2.719
2.785

The mean anode density of MPE III anode specification manufactured by MPE was 2.745 g/cm3.

VISUAL EXAMINATION

Photos after test to show the consumption pattern are shown below (Consumption pattern on the surface of anode samples fairly even corrosion throughout):











Microstructure Test of Anode Test Specimens after exposure

Five samples were selected for microstructure test conducted by certified laboratory (contact us for details). The visual microscopy of cross-section on all 5 samples shows NO indication of INTERGRANULAR CORROSION. The results and photomicrographs of the microstructure are available online .. .. view this report.


ELECTROCHEMICAL RESULT

CALCULATION OF CURRENT CAPACITY
Current capacity (ampere. Hours/kg ) = (c x 1,000) / w
where,
c = Total charge passed in a year (amp. h)
w = Weight loss of anode samples (grams)
The results are given in Table 5.

Table 5 : Result of Anode Current Capacity and Consumption Rate

Test
Specimen
 Initial
Weight
(G)		 Final
Weight
(g)		 Weight
Loss
(g)		 Total hours
of
Experiment
 Total
Current Flow
(Amp.Hrs)		 Consumption
Rate
(Kg/Amp.Yr)		 Current
Capacity
(Amp.Hr / Kg)
1A 154.060 5.743 148.317 8760 399.53 3.252 2693.76
1B 153.850 4.570 149.28 8760 399.53 3.273 2676.38
2A 153.206 8.915 144.291 8760 399.53 3.164 2768.92
2B 152.915 5.079 147.836 8760 399.53 3.241 2702.52
3A 154.512 5.679 148.833 8760 399.53 3.263 2684.42
3B 153.624 5.701 147.923 8760 399.53 3.243 2700.93
4A 153.641 2.570 151.071 8760 399.53 3.312 2644.65
4B 153.182 3.886 149.296 8760 399.53 3.273 2676.09
5A 153.961 7.724 146.237 8760 399.53 3.206 2732.07
5B 153.146 5.503 147.643 8760 399.53 3.237 2706.05


The mean anode current capacity was 2698.58 +/- 50 Amp.Hr/kg and consumption rate was 3.246 Kg/Amp.yr.

Result of Potential Test Measurement
Anode potential were measured against reference electrode Silver/Silver Chloride (Ag/AgCl) on a weekly basis.

Determination of Anodic Current Density
The voltage drops across 10 ohms resistor were measured to calculate the anodic current density. The shunt of capacity 10mV = 1mA was used for the measurement.

Current Density (mA/cm2) = Actual Current Flow (mA) / Exposed Anode Surface Area (cm2)

The graph of anode potential versus duration of exposure (week) and current densities versus duration of exposure (week) are presented in figures 7 to 16.

The results shown in figure 7 to 16 indicate that no passivation of the anodes occurred.

Figure 7: Anode Potential versus Duration of Exposure (weeks) – Test Specimen No. 1A and 1B

Figure 8: Current Densities versus Duration of Exposure(weeks)– Test Specimen No. 1A and 1B

Figure 9: Anode Potential versus Duration of Exposure (weeks) – Test Specimen No. 2A and 2B

Figure 10: Current Densities versus Duration of Exposure(weeks)– Test Specimen No. 2A and 2B

Figure 11: Anode Potential versus Duration of Exposure (weeks) – Test Specimen No. 3A and 3B

Figure 12: Current Densities versus Duration of Exposure(weeks)– Test Specimen No. 3A and 3B

Figure 13: Anode Potential versus Duration of Exposure (weeks) – Test Specimen No. 4A and 4B

Figure 14: Current Densities versus Duration of Exposure (weeks)– Test Specimen No. 4A and 4B

Figure 15: Anode Potential versus Duration of Exposure (weeks) – Test Specimen No. 5A and 5B

Figure 16: Current Densities versus Duration of Exposure(weeks)– Test Specimen No. 5A and 5B
Conclusion
The mean current capacity of MPE III anode specification manufactured by MPE Lindung Sdn Bhd was 2698.58 +/- 50 Amp.Hr/kg and consumption rate was 3.246 Kg/Amp.yr complies to DNV RPB40 table 6.6.1.

The anodic current density Is 0.49 mA/cm2 and potential is -1055.71mV VS AglAgCI (seawater) reference electrode.

No indication of passivation were found.

No intergranular corrosion was found.

End of report. (for a pdf version of this report, click here)
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