Brazing stainless steel

[webcraft]

I have just removed our stemhead fitting to have it repaired and beefed up. I took it to a friend who has a fully equipped engineering workshop and is a whizz with metals of all kinds, but his normal area of work expertise is restoring vintage motorcycles, not boats.

He wanted to braze reinforcements on, as brazing is stronger than stainless welding. However, I am concrned that the brazing alloy used (aluminium based, I believe) will quickly corrode due to galvanic action, and the reinforcing plates will simply fall off. My friend disagrees, so it's over to the forum in the hope that there is a marine metallurgist (or two) lurking in the wings somewhere. Is brazing ever suitable for joining stainless in the marine environment?

One other question while I am on the subject . . . . will the use of non-A4 stainless (I believe the exact grade is 303) reinforcements lead to any problems? Looking at a galvanic table it would seem that galvanic action won't be a problem, but I assume that lesser grades of stainless will develop brown staining much quicker.

- Nick

 

[pjs100]

Nick, as you suggest you will have both galvanic and aesthetic problems if you braze. TIG welded 316 stainless is generally recommended for best results in seawater but you may be able to get away with 304 on the topside.
JJTOP

 

[Freebee]

304 gets surface corrosion in sea water that can admmitedly be cleaned off with scotch brite but is unsightly, 303 has less corrosion resistance than 304, so I would say 316 every time for marine use.

 

[Avocet]

I haven't a clue what Avocet's pulpit is made of (some grade of stainless) but it is definitely brazed and doesn't seem to have shown any signs of corrosion in the last 30 years. About 5 years ago, it got broken (extreme abuse, definitely not ordinary wear & tear) and it was brazed again (unfortunately, I know not what with) and it still seems fine.

 

[Norman_E]

A lot of so called brazing, is actually silver soldering. Originally brazing used brass wire and borax for flux, I have done it that way on mild steel. Nowadays silver solders are pretty sophisticated alloys, with special grades of rod for stainless steel. As the alloys used have a silver content they tend to be quite high up the galvanic scale. I see no reason why silver soldering should not be used in a marine environment (above the waterline) but correct choice of rod and flux will be essential for a successful joint. Having said that MIG welding is probably the preferred route, if only because a large stainless steel part will need a mighty gas blowtorch to get sufficient heat for a good silver soldered joint.

 

[charles_reed]

Is unusual.

There are advantages - less local distortion due to the lower temperatures used and, if thin-walled tube, less likelihood of blowing a hole in it when striking.

304 is OK for above waterline use but 316 is better all round.

No problems of corrosion from the brazing, but definite cost implications using it in preference to normal TIG with stainless rod.

 

[Heckler]

i may be a very rude person but i can tell you that brazing stainless is not a problem, dont get it too hot or the braze wont take, galvanic is not a prob either, i always speak from first hand knowledge, when i learned to scuba dive 30 odd years ago it was the time of make your own gear, i brazed 1/2" stainless tube together to make a back pack to hold the air bottle and never had a minutes problem with corrosion galvanic or other.