stainless / bronze corrosion

[Dan Irvine]

Hi, pesky gunstock bolt, panic door hardware, chicago screw, "barrel nut" guy here again. See Gunstock Bolt below for thread. Pacific Fasteners in Burnaby BC carrys stainless barrel nuts up to 3/8". My spreader tangs are silicon bronze. These fittings are well above the water, hopefully most of the time anyways. Am I asking for trouble using the stainless nuts on bronze rod? Should I just use stainless rod and nuts to throughbolt the spreader tangs? Is this even an issue with a freshwater boat? I promise to do 3 hours upside down paint scraping and memorize the ancient mariner backwards in Croation as pennance for all these questions.

[Donn]

Can't speak for freshwater on this, but I just replaced mixed bronze/SS nuts and bolts on a shaft log, and they were seriously corroded. To be fair, one end of each bolt was always in saltwater, and the nut and other end of the bolt was occasionally in saltwater.

[Ian G Wright]

I'd be inclined to put ss nuts on ss bolts and bronze nuts on bronze bolts etc etc..
however my rigging screws and chain plates are bronze but the clevis pins are 1/2 inch stainless as are all the split pins. Regularly soaked in sea water as you might expect. The only sign of 'rust' is on a couple of the clevis pins. No actual damage, just a rust coloured stain because, I suspect, the pins were turned using a cutting tool that had been used for working mild steel. A common problem, but cosmetic only.

IanW.

[ 10-03-2002, 04:47 AM: Message edited by: Ian G Wright ]

[Wilson Fitt]

I don't think that bronze and stainless would cause any problem. Certainly, it should be just fine up in the air on a freshwater boat.

Bronze turnbuckles are always in contact with stainless rigging wire terminals and no-one raises an eyebrow. Some turnbuckles have stainless bodies and bronze shanks to avoid the problem of galling or binding that occurs in high load stainless on stainless threads. I have occassionaly used a bronze nut on a stainless bolt for that reason as well.

[Ed Nye]

I think this a great thread. Opal has a bronze fitting connected to another with a stainless pin. The pin and cotter keys are always under water. I have never seen any corrosion. On the other hand, I have always been told never mix them.

There has to be an authority around someplace,
Ed

[Donn]

I'll paraphrase Nigel Calder with a highly simplified statement. If you place dissimilar metals in the same electrolyte, the less noble of the two metals will receive current flow from the other, and will suffer galvanic corrosion.

The key word is electrolyte. Saltwater is one, and fresh water isn't.

[Bryan Mehus]

I also believe you will be just fine. There is often a problem with galling of stainless bolt/nut fastenings, and sometimes bronze nuts are used with stainless bolts to alleviate the problem, notably outboard transom bolts.

[Ed Nye]

It's not so much that a metal is dissimilar, but how far apart they are. Two bolts of the same metal will not be absolutely the same unless they came out of the same pot. Here is one person/groups opinion

GALVANIC SERIES OF METALS AND ALLOYS

CORRODED END ( ANODIC OR LEAST NOBLE)

MAGNESIUM
MAGNESIUM ALLOYS
ZINC
ALUMINUM 5052, 3004, 3003, 1100, 6053
CADMIUM
ALUMINUM 2117, 2017, 2024
MILD STEEL (1018), WROUGHT IRON
CAST IRON, LOW ALLOY HIGH STRENGTH STEEL
CHROME IRON (ACTIVE)
STAINLESS STEEL, 430 SERIES (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) INCONEL 625 (ACTIVE) TITANIUM (ACTIVE)
LEAD - TIN SOLDERS
LEAD
TIN
INCONEL 600 (ACTIVE)
NICKEL (ACTIVE)
60 NI-15 CR (ACTIVE)
80 NI-20 CR (ACTIVE)
HASTELLOY B (ACTIVE)
BRASSES
COPPER (CA102)
MANGANESE BRONZE (CA 675), TIN BRONZE (CA903, 905)
SILICONE BRONZE
NICKEL SILVER
COPPER - NICKEL ALLOY 90-10
COPPER - NICKEL ALLOY 80-20
430 STAINLESS STEEL
NICKEL, ALUMINUM, BRONZE (CA 630, 632)
MONEL 400, K500
SILVER SOLDER
NICKEL (PASSIVE)
60 NI- 15 CR (PASSIVE)
INCONEL 600 (PASSIVE)
80 NI- 20 CR (PASSIVE)
CHROME IRON (PASSIVE)
302, 303, 304, 321, 347, STAINLESS STEEL (PASSIVE)
316, 317, STAINLESS STEEL (PASSIVE)
CARPENTER 20 CB-3 STAINLESS (PASSIVE), INCOLOY 825NICKEL - MOLYBDEUM - CHROMIUM - IRON ALLOY (PASSIVE)
SILVER
TITANIUM (PASS.) HASTELLOY C & C276 (PASSIVE), INCONEL 625(PASS.)
GRAPHITE
ZIRCONIUM
GOLD
PLATINUM

PROTECTED END (CATHODIC OR MOST NOBLE)

And here is anothers opinion: http://www.corrosionsource.com/handbook/galv_series.htm

Ed