4300
Catalog
General Technical
T18
Parker Hannifin Corporation
Tube Fittings Division
Columbus, Ohio
http://www.parker.com/tfd
Table T14 — Electromotive
or Galvanic Series for Metals
The susceptibility of different base metals to corrosion
while incontact, depends upon the difference between the
contact potentials, or the electromotive voltages of the
metals involved. The greater the potential difference is,
the greater is the tendency for corrosion. The metal with
the higher potential forms the anode and is corroded.
In other words, the larger the separation distance in
the electromotive chart between the two metals in
contact, the higher the contact potential and
chances for corrosion. For example, zinc and
aluminum are very short distance apart in the chart;
therefore potential for corrosion when these two metals are
in contact is very low. On the other hand, aluminum and
passivated 316 stainless steel are far apart; hence, when in
contact, the potential for corrosion is very high. Aluminum,
being more anodic metal, will corrode in this combination.
As a general guideline, if the metals are half the length of the
chart ormoreapart, thecombination shouldbeavoided. Also,
it is not a good idea to combine an anodic metal part with
thin cross section, such as thin wall tubing, with a cathodic
or less anodic metal part of a heavy cross section, such as
a fitting.
Corrosion of Base Metals in Contact
Electromotive or Galvanic Series for Metals
Electric current flows from plus to minus
Direction of attack
Magnesium
Magnesium Alloys
Zinc (Parker steel fittings are zinc plated)
Zinc-Nickel (Parker XTR Plating)
Beryllium
Aluminum 5052, 3004, 3003, 1100, 6053
Cadmium
Aluminum 2117, 2017, 2024 T4
Mild steel (1018), wrought iron, free machining steel (12L14)
Low alloy high strength steel, cast iron
Chrome iron (active)
430
Stainless (active)
302, 303, 321, 347, 410, 416,
stainless steel (active)
Ni-resist
316, 317
stainless steel (active)
Carpenter 20Cb-3 stainless (active)
Aluminum bronze (CA 687)
Hastelloy C (active) Inconnel 625 (active) Titanium (active)
Lead/Tin solder
Lead
Tin
Inconnel 600 (active)
Nickel (active)
60
Ni-15 Cr (active)
80
Ni-20 Cr (active)
Hastelloy B (active)
Naval brass (CA 464), Yellow brass (CA 268), Brass (CA360)
Red brass (CA 230), Admiralty brass (CA 443)
Copper (CA 102)
Maganese bronze (CA 675), Tin bronze (CA 903, 905)
410, 416
Stainless (passive) Phospher bronze (CA 521, 524)
Silicon bronze (CA 651, 655)
Nickel silver (CA 732, 735, 745, 752, 754, 757, 764, 770, 794)
Cupro Ni 90-10
Cupro Ni 80-20
430
Stainless steel (passive)
Cupro Ni 70-30
Nickel aluminum bronze (CA 630, 632)
Monel 400, K500
Silver solder
Nickel (passive)
60
Ni 15 Cr (passive)
Inconnel 600 (passive)
80
Ni 20 Cr (passive)
Chrome iron (passive)
302, 303, 304, 321, 347
stainless steel (passive)
316, 317
stainless steel (passive) (Parker stainless steel fittings are passivated)
Carpenter 20 Cb-3 stainless (passive), Incoloy 825
Silver
Titanium (passive), Hastelloy C & C276 (passive), Inconnel 625 (passive)
Graphic
Zirconium
Gold
Platinum
-
Cathodic
(
most noble)
protected
+ Anodic
(
least noble)
corroded
M
Example:
A thin wall brass tube with
steel fitting is a better, although not ideal,
combination than a thin wall steel tube
with brass fitting.
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