WATE R C OOL ED D EV I CES

Galvanic Corrosion Prevention

Guide for Water Cooling Systems
November 2017 | White Paper

Water
Created by Cooled
Helen E. Kane, Advanced Energy Industries, Inc. Devices

Abstract
Table of Contents
This report details best practices for reducing the risk of
galvanic corrosion in water cooling system designs. Galvanic Summary and Background 2
corrosion will manifest if the following conditions exist: Research Findings 2
Best Practices Recommendations 5
1 E
 lectrically dissimilar metals in contact (or both in
References7
contact with the same water)

2 Electrolyte present (could be as simple as condensation)

Time is another critical factor. The mean time to failure

can be short or long, depending on the combination of
conditions 1 and 2. This report provides the galvanic series
for general metals and compatibility. In addition, it lists
preventative measures to avoid issues in open loop cooling
water systems.
2 G A LVA NI C CORROSI ON PRE V E NTION GU ID E FOR WAT ER COOLIN G SYST EMS

Summary and Background

This report details best practices for reducing the risk of galvanic corrosion in mechani-
cal and electro-mechanical cooling system designs. Galvanic corrosion, sometimes called
bimetallic or dissimilar metal corrosion, is when one metal in a system experiences corrosion
due to an electro-chemical reaction with a different metal and an electrolyte in the same
system. Galvanic corrosion has been experienced in designs with dissimilar metals used in
Advanced Energy products that use water cooling. Because conditions that promote gal-
vanic reactions can exist inside Advanced Energy units due to the environment and running
conditions, some simple best practices will help reduce the risk of galvanic corrosion failure.

Research Findings

Galvanic corrosion will occur when cathodic and anodic metals are in contact in humid, salty,
or outside environments, or in and around water systems. The potential for different metals
to be an anode verses a cathode is listed in Table 1. The larger the difference between two
materials in this list, the larger the potential for galvanic corrosion. Testing for a material’s
anode potential is generally done in saltwater; however, reactions will occur in simple humid
environments as well.

Table 1A: Galvanic Series in Flowing Seawater 1

Voltage Voltage
Range of Alloy Range of Alloy
vs. Reference vs. Reference
Alloy Electrode* Alloy Electrode*

Magnesium -1.60 to -1.63 400 Series Stainless Steels ** -0.20 to -0.35

Anodic or Active End

Zinc -0.98 to -1.03 90-10 Copper-Nickel -0.21 to -0.28

Aluminum Alloys -0.70 to -0.90 Lead -0.19 to -0.25

Cadmium -0.70 to -0.76 70-30 Copper-Nickel -0.13 to -0.22

Cast Irons -0.60 to -0.72 17-4 PH Stainless Steel † -0.00 to -0.15

Steel -0.60 to -0.70 Silver -0.10 to -0.20

Aluminum Bronze -0.30 to -0.40 Monel -0.04 to -0.14

Red Brass, Yellow Brass, Naval Brass -0.30 to -0.40 300 Series Stainless Steels ** † -0.00 to -0.15

Copper -0.28 to -0.36 Titanium and Titanium Alloys † +0.06 to -0.05

Cathodic or Noble End

Lead-Tin Soldier -0.26 to -0.35 Inconel 625 † +0.10 to -0.04

Admiralty Brass -0.25 to -0.34 Hastelloy C-276 † +0.10 to -0.04

Manganese Bronze -0.25 to -0.33 Platinum † +0.25 to +0.18

Silicon Bronze -0.24 to -0.27 Graphite +0.30 to +0.20

* These numbers refer to a Saturated Calomel Electrode.

** In low-velocity or poorly aerated water, or inside crevices, these alloys may start to corrode and exhibit potentials near -0.5 V.
† When covered with slime films of marine bacteria, these alloys may exhibit potentials from +0.3 to +0.4 V.
3 G A LVA NI C CORROSI ON PRE V E NTION GU ID E FOR WAT ER COOLIN G SYST EMS

Table 1B 2

MOST NOBLE — CATHODIC LEAST NOBLE — ANODIC

0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 -1.4 -1.6

Magnesium

Zinc

Beryllium

Aluminum alloys

Cadmium

Mild steel & cast iron

Low alloy steel

Austenitic cast iron

Aluminum bronze

Naval brass, yellow brass & red brass

Tin

Copper

50/50 lead tin solder

Admiralty brass, aluminum brass

Manganese bronze

Silicon bronze

Stainless steel — grades 410, 416

Nickel silver

90/10 copper nickel

80/20 copper nickel

Stainless steel — grade 430

Lead

70/30 copper nickel

Nickel aluminum bronze

Nickel chromium alloy 600

Nickel 200

Silver

Stainless steel — grades 302, 304, 321 & 347

Nickel copper alloys — 400, K500

Stainless steel — grades 316 & 317

Alloy 20 stainless steel

Nickel iron chromium alloy 825

Titanium

Gold, platinum

Graphite
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Table 2 3

Anodic
Metallurgical Category Index (V)

Gold, solid and plated, gold-platinum alloy 0.00

Rhodium plated on silver-plated copper 0.05

Silver, solid or plated; monel metal. High nickel-copper alloys 0.15

Nickel, solid or plated, titanium alloys, Monel 0.30

Copper, solid or plated; low brasses or bronzes; silver solder; German silvery high copper-nickel alloys; 0.35
nickel-chromium alloys

Brass and bronzes 0.40

High brass and bronzes 0.45

18% chromium type corrosion-resistant steels 0.50

Chromium plated; tin plated; 12% chromium type corrosion-resistant steels 0.60

Tin-plate; tin-lead solder 0.65

Lead, solid or plated; high lead alloys 0.70

Aluminum, wrought alloys of the 2000 Series 0.75

Iron, wrought, gray or malleable, plain carbon and low alloy steels 0.85

Aluminum, wrought alloys other than 2000 Series aluminum, cast alloys of the silicon type 0.90

Aluminum, cast alloys other than silicon type, cadmium, plated and chromate 0.95

Hot-dip-zinc plate; galvanized steel 1.20

Zinc, wrought; zinc-base die-casting alloys; zinc plated 1.25

Magnesium & magnesium-base alloys; cast or wrought 1.75

Beryllium 1.85

Extensive research and experimentation show galvanic corrosion occurring in metals with
an anodic index difference of as little as 0.15V depending on the environment, and some
metals have been known to corrode with potentials of -0.5V. It should also be noted that if
the dissimilar metals are simultaneously in contact with the same water, and that water is
electrically charged, corrosion will occur. In addition, in very highly energetic interactions
between copper and aluminum in water, the small amounts of nitrate and sulphate in the
water can be reduced to ammonia and sulphides that will attack the copper, thereby causing
the copper to corrode despite it being the cathode in the system.

It is important to note that some non-metallic materials have been found to promote galvanic
reactions as well: cellulosic reinforced plastics, carbon or metal loaded resin materials and
asbestos-cement composites. These non-metallic materials should be avoided.
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The galvanic series chart created by the organization Preservation Science (shown in Table 3),
rates the interaction between specific base metals and different fastener materials. This chart
can be referenced to determine the best fasteners to use to reduce the risk of galvanic corrosion.

Table 3: Fastener Effects4

The following chart can be used to guide the selection of fasteners based on galvanic action:

Fastener Metal

Brasses, Austenitic
Zinc & Aluminum & Martensitic
Steel & Copper, Stainless Steel
Galvanized Aluminum Stainless (Type
Cast Iron Bronzes, (Type 302/304,
Steel Alloys 410)
Base Metal Monel 303, 305)

Zinc & Galvanized Steel A B B C C C

Not
Aluminum & Aluminum Alloys A A B C B
Recommended

Steel & Cast Iron AD A A C C B

Teme (Lead Tin) Plated

ADE AE AE C C B
Steel Sheets

Brasses, Copper, Bronzes, Monel ADE AE AE A A B

Ferritic Stainless Steel

ADE AE AE A A A
(Type 430)

Austenitic Stainless Steel

ADE AE AE AE A A
(Type 302/304)

Key:
A. Corrosion of the base metal is not increased by the fastener.
B. Corrosion of the base metal is marginally increased by the fastener.
C. Corrosion of the base metal is markedly increased by the fastener material.
D. Plating on the fasteners is rapidly consumed, leaving the bare fastener metal.
E. Corrosion of the fastener is increased by the base metal.

Best Practice Recommendations

Due to extensive research on galvanic corrosion over the years, galvanic series lists and best
practices for prevention are well documented. The best practices for reducing the risk of
galvanic corrosion are listed below.

1. Select metals/alloys as close together as possible in the galvanic series.

a. G
 alvanic corrosion can occur in metals that are 0.15V different on the galvanic series.
Remember that in a water system any two metals that share contact with the same water
will be susceptible to corrosion, if notably dissimilar or in a charged environment.
b. For fasteners, use the same metal or a more cathodic metal than the part being fastened.
6 G A LVA NI C CORROSI ON PRE V E NTION GU ID E FOR WAT ER COOLIN G SYST EMS

2. Design interface metals such that the area of the cathode is much smaller than the area of the
more anodic metal. For example, use a stainless steel screw in aluminum but not the reverse. The
amount of galvanic corrosion is proportional to the cathode/anode area ratio. A small anode and large
cathode will result in large galvanic corrosion.

3. Insulate dissimilar metals wherever practical.

a. Use compatible gaskets or washers between dissimilar metals prior to fastening.
b. Do not use non-metallic materials that have salts, acid or alkaline materials, carbon or metallic
particles, are subject to bio-deterioration, support fungal growth, or absorb or wick water.

4. Apply coatings with caution. If coatings must be used, coat the cathode with a metal
compatible with the anode.
a. Coatings must be inspected and maintained.
b. Apply corrosion-inhibiting pastes or compounds under small screw heads of dissimilar
metal surfaces, even if plated.
c. Seal all faying edges to prevent the entrance of moisture.
d. Coat external joints of dissimilar metals when possible, to prevent exposure to moisture.

5. Avoid threaded joints for materials far apart in the galvanic series.
a. T
 hreading creates small contact areas that corrode quickly.
b. Coatings are damaged by the act of threading the joint together.

6. Do not use deionized/distilled water

a. While deionized/distilled water carries very little charge, it is known to be highly corrosive
to copper as well as several other metals.
b. Deionized water will rip Cu ions from any copper in the system, contaminating the water
and corroding any copper in the system. The Cu ion tear-off process is accelerated by
the higher temperatures and water speeds that exist locally inside the power generator
cooling systems.

7. G
 round power supplies per manufacturer recommendations to avoid charging the cooling
water.
a. Improper grounding of a unit can result in corrosion from stray current.
b. Ways to prevent stray current corrosion:
i. Find the source of the stray current and stop leakage by proper grounding and
insulation.
ii. Offset the corrosion effects of the current by installing an impressed cathodic
protection system.

8. Avoid condensation inside system generators.

a. Condensation is enough electrolyte to promote corrosion.
b. Cooling water flowing through a power supply while the unit is not providing output can
cause condensation to form inside the unit. Condensation can cause internal device shorts
as well as corrosion.
c. Shutting down the water flow while units are not running via a solenoid, or some equivalent
method, will protect against condensation-caused corrosion.
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References
Works cited:

1 Corrosion. Accessed August 4, 2017. http://I-36.com/corrosion.php

2 “CORROSION: GALVANIC CORROSION.” SSINA: Stainless Steel: Corrosion. Accessed August 4, 2017. http://www.ssina.com/corrosion/
galvanic.html.

3 Edge, LLC. Engineers. “Galvanic and Corrosion Compatibility Dissimilar Metal Corrosion.” Engineers Edge. Accessed August 5, 2017. http://
www.engineersedge.com/galvanic_capatability.htm.

4 Preventing Galvanic Corrosion. Accessed August 4, 2017. http://www.preservationscience.com/materials/metals/PGC.html.

Other sources:

Myers and Cohen. “Pitting Corrosion of Copper in Cold Potable Water Systems”, Reprinted from Materials Performance Vol. 34, No 10, pp 60-
62 (1995) by NACE International.

Dillon, Desch, Lai. The Nalco Guide to Cooling Water Systems Failure Analysis, London, McGraw-Hill Education, 2014.

Foundation for Water Research, Review of Current Knowledge: Causes of Copper Corrosion in Plumbing Systems, 1998

http://www.corrosionclinic.com/types_of_corrosion/stray%20current%20corrosion.htm

http://www.ssina.com/corrosion/galvanic.html

http://l-36.com/corrosion.php

http://www.npl.co.uk/upload/pdf/bimetallic_20071105114556.pdf

ASM Handbook, Vol. 13, Corrosion of Titanium and Titanium Alloys, p. 675.

http://corrosionjournal.org/doi/abs/10.5006/1.3585192?code=nace-prem-site

http://www.corrosionclinic.com/types_of_corrosion/galvanic_corrosion.htm

http://www.clufix.com/de/images2/plaquette_revetements_en.pdf#page=7

http://www.preservationscience.com/materials/metals/PGC.html

https://www.thebalance.com/galvanic-corrosion-2339698

http://www.engineersedge.com/galvanic_capatability.htm

Specifications are subject to change without notice.

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