stainless steel to brass

KEVMAR · Sep 29, 2016

on my 36 albin trawler the railing is teak and where the opening is is attached with brass fittings. Can I use stainless steel screws to attach the fitting to the teak railing.... in other words can I use the stainlaess steel screws with the brass?? thanks

cappy208 · Sep 29, 2016

Yup. SS is fine. Just aesthetic. Were these hinges originally chromed bronze? Did the heads get buggered up?

boatpoker · Sep 29, 2016

You sure it's not bronze. Brass won't last long if exposed to salt while touching a metal higher on the galvanic scale which bronze and stainless steel are ... the brass will weaken due to a process known as dezincification.

FF · Sep 30, 2016

". the brass will weaken due to a process known as dezincification."

TRUE , but it usually requires the brass to be constantly submerged in an electrolite like sea water.

boatpoker · Sep 30, 2016

FF said:
". the brass will weaken due to a process known as dezincification."

TRUE , but it usually requires the brass to be constantly submerged in an electrolite like sea water.

Not at all. Moist salt molecules are enough.

foggysail · Sep 30, 2016

FF said:
". the brass will weaken due to a process known as dezincification."

TRUE , but it usually requires the brass to be constantly submerged in an electrolite like sea water.

Boatpoker has it correct. It may take longer than if submerged but the culprit here is oxygen and couple that with humidity there is an electrical path. This is the same reason a hunk of steel ... no not stainless.....will rust even in a so called dry desert.

sdowney717 · Sep 30, 2016

SS is stronger and will last longer above the waterline. Most of my SS screws are in perfect shape, while the brass or even bronze were not on my 45 year old Egg Harbor. The bronze or brass were corroded, stuck in the wood, or broken. You can't trust old brass screws, they may snap when reusing them.

boatpoker · Sep 30, 2016

Stainless steel screws will not last long screwed into moist wood, crevice corrosion will be the result. The best choice is bronze. The problem these days is that the market is flooded with alloys purporting to be bronze when they actually have too high a zinc content to fall into the bronze family and are really brass's. Compounding the confusion id the nomenclater i.e. Naval or Admiralty bronze are actually brass. For any critical application the fasteners should be purchased from a trusted and knowledgeable supplier. Home Depot is the Chinese metallurgist's best friend.

PS. ABYC Certified Corrosion Analyst.

sdowney717 · Sep 30, 2016

boatpoker said:
Stainless steel screws will not last long screwed into moist wood, crevice corrosion will be the result. The best choice is bronze. The problem these days is that the market is flooded with alloys purporting to be bronze when they actually have too high a zinc content to fall into the bronze family and are really brass's. Compounding the confusion id the nomenclater i.e. Naval or Admiralty bronze are actually brass. For any critical application the fasteners should be purchased from a trusted and knowledgeable supplier. Home Depot is the Chinese metallurgist's best friend.

PS. ABYC Certified Corrosion Analyst.

No problems with wood on my wood boat above the waterline and any SS screws.
Wood is not wet enough unless it is submerged to damage SS screws. I speak from empirical experience and replacing many thousands of screws in wood. I rescrewed my teak deck using SS deck screws 18-8 from Home Depot years ago and they are perfect. I have even pulled some out to see. That teak deck is screwed onto 2x4 beams. I also completely removed every bottom plank on the hull, re screwed with 4000 number 2 square drive bronze screws from McFeeley's. I have owned this boat since 1998 and done lot of work on it.
I have these 2 teak stair steps on both sides of the aft deck. They have bronze angles and SS screws were used to attach to the teak. I recently pulled them out to redo the teak finish and they were again perfect. Now those screws were put in before 1998 when I bought the boat.

My wood toerail, attached with big bronze screws or brass, many were corroded and broken. In 2000, I removed the toe rail, rebedded them and attached all using SS 18-8 3 inch long deck square drive deck screws. And the toerails have not budged. the wood is mahogany.

Thing is people who build decks, is just like boat decks, and SS screws work great in the rain and corrosive arsenic treated wood.

Go to the wooden boat forum and ask them if SS screws are fine above the waterline, and you will find they say yes.

I did some plank work on the hull above the water line. And most of the bronze screws were corroded and many stuck tight in the oak frames. They were still strong enough as is, except for the but blocks where most were wasted away.

boatpoker · Sep 30, 2016

sdowney717 said:
No problems with wood on my wood boat above the waterline and any SS screws.
Wood is not wet enough unless it is submerged to damage SS screws. I speak from empirical experience and replacing many thousands of screws in wood. I rescrewed my teak deck using SS deck screws 18-8 from Home Depot years ago and they are perfect. I have even pulled some out to see. That teak deck is screwed onto 2x4 beams. I also completely removed every bottom plank on the hull, re screwed with 4000 number 2 square drive bronze screws from McFeeley's. I have owned this boat since 1998 and done lot of work on it.
I have these 2 teak stair steps on both sides of the aft deck. They have bronze angles and SS screws were used to attach to the teak. I recently pulled them out to redo the teak finish and they were again perfect. Now those screws were put in before 1998 when I bought the boat.

My wood toerail, attached with big bronze screws or brass, many were corroded and broken. In 2000, I removed the toe rail, rebedded them and attached all using SS 18-8 3 inch long deck square drive deck screws. And the toerails have not budged. the wood is mahogany.

Thing is people who build decks, is just like boat decks, and SS screws work great in the rain and corrosive arsenic treated wood.

Go to the wooden boat forum and ask them if SS screws are fine above the waterline, and you will find they say yes.

I did some plank work on the hull above the water line. And most of the bronze screws were corroded and many stuck tight in the oak frames. They were still strong enough as is, except for the but blocks where most were wasted away.

The chemistry and process of crevice corrosion is well known. You can read up on it at NACE It's not the water that does the damage but the exclusion of oxygen.

"big bronze screws or brass, many were corroded and broken" Don't you know if they were bronze or brass and if so what alloy?

DHeckrotte · Sep 30, 2016

I was gonna' say that the bronze fittings should be fastened with bronze screws, and that stainless would be a poor choice in contact with the bronze. Not so true as I would have thought; see the table below. It makes a difference which metal is in the majority, too, that is, whether the bronze is in the screw holding the stainless or vice versa.

I've enjoyed plenty of failing bronze and brass screws in various situations. Most recently: the screws holding the stainless steel ceiling fixtures in this boat were chrome-plated brass. I've spent time poking the dezincified brass out of the fixture to make room for new stainless steel machine screws.

I restored/rebuilt a mid-50's Flying Dutchman sailboat. I removed all the brass and/or bronze screws, ring nails, etc. Some were original, some were the PO's repairs. Some were perfect, most were various degrees of dezincified or otherwise corroded. In some areas, the wood was corroded as well (architects and wood boat restorers call it 'nail sickness'). I replaced all the fasteners with mahogany dowels set in epoxy.

sdowney717 · Sep 30, 2016

boatpoker said:
The chemistry and process of crevice corrosion is well known. You can read up on it at NACE

"big bronze screws or brass, many were corroded and broken" Don't you know if they were bronze or brass and if so what alloy?

I figure the ones in the toe rail were brass.
It is not easy to tell, when the screws get old they all turn various shades of browns and green.
The hull screws were - are everdure bronze.
I went up a size to number 14's 1 3/4 inch for the hull. If you go with #2 square drive, they are much harder to strip the heads than the more common #1.

Typically bronze screws can last a few decades in salt water, then you need to rescrew. My boat made in 1970, I rescrewed in 2005. About half the screws were good, the other half degraded, some become like bronze nails. Hard to get out were some screws, if you pull the entire plank, not too bad then.
I was pumping evey 15 minutes, and had little crabs living in the bilge. I knew I had to fix it.
I also sealed the hull with an impervious rubber coating. So when I go in, no more need to soak up the wood.

Yes I know all about crevice corrosion and SS, I have a wood boat. 18-8 SS will erode if in the bottom planks. Seen it myself on the boat. Never seen that in any above the waterline usage.

boatpoker · Sep 30, 2016

sdowney717 said:
I figure the ones in the toe rail were brass.
It is not easy to tell, when the screws get old they all turn various shades of browns and green.
The hull screws were - are everdure bronze.
I went up a size to number 14's 1 3/4 inch for the hull. If you go with #2 square drive, they are much harder to strip the heads than the more common #1.

Typically bronze screws can last a few decades in salt water, then you need to rescrew. My boat made in 1970, I rescrewed in 2005. Also sealed the hull with an impervious rubber coating.

"Square drive", I believe the patent (Canadian invention) calls them "Robertson screws"

Sealife · Sep 30, 2016

After another thread going here I am hesitant to contribute for several reasons.....but.

If, there has to be dissimilar metals in contact, please always use the most noble fastner in the least noble material ie: stainless bolts in aluminum, never aluminum bolt in stainless.. It has to do with the mass of the object. Always get them as close as possible!

Granted this has nothing to due with crevice corrosion.

RT Firefly · Sep 30, 2016

Greetings,
Mr. bp. Unfortunately, "Robertson" screws do not exist in the US. They are all "square drive". Although, I was in BOW (Boat Owner's Warehouse) in Ft. Lauderdale a number of years back looking for said "Robertson" screws and one of the older employees actually knew the proper name but confessed he only knew them as Hatteras screws.

boatpoker · Sep 30, 2016

Mr. Robertson did not handle his patent well and got left by the wayside. The Robertson factory was still in Milton, Ontario when I lived there 30yrs. ago.

It took me 10 years on my first boat to replace every stinking phillips with a Robertson, 6 years on my second boat and I am still working on that on DIRT FREE.

RT Firefly · Sep 30, 2016

Greetings,
Mr. bp. Oh, I'm quite aware of Mr. Robertson's business decisions anecdotally explained by his Scottish ancestry. I did find that Fastenall will order "Robbies"...er...Square drives.

boatpoker · Sep 30, 2016

RT Firefly said:
Greetings,
Mr. bp. Oh, I'm quite aware of Mr. Robertson's business decisions anecdotally explained by his Scottish ancestry. I did find that Fastenall will order "Robbies"...er...Square drives.

Being born and bred in Scotland I find that ........ accurate

stainless steel to brass

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