Bronze vs Stainless

[Dirk]

Ongolo and Cliff

Gentelmen, You are both a credit to this forum for your replies (none of which show even a hint of bovine excrement) but more importantly for your good manners and polite courtesy.

How refreshing!

Cheers

Dirk

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[cliff]

"Cliff, there is a little omission in your table. It does not show what metal has been used as a standard reference voltage."
Nope, no omission - standard hydrogen cell

"Further even if ss is not passivated it is always more positive than iron."
In general I would agree but... It is not always the case. Depends on the condition of the stainless heat treatment, hot drawn, cold drawn, surface condition.

"And here we use a mixture of HCL and peroxide to passivate when nothing else is on hand."
Interesting, never came across that one before, usually either Nitric acid or more recently Citric acid (more environmentally friendly) although certainly the peroxide is a strong oxidiser which is needed for the passivation and the Hydrochloric would clean the surface but I would not be happy with the Cl ions floating about in the soln. but if it works go for it.

Ever carried out a copper sulphate test or ferroxyl test on stainless passivated using HCl and peroxide? Here we go talking shop instead of boats! How dull get enough of this at work - oh dear there is that 4 letter word again time to go pump the bilges.


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[MainlySteam]

It is not only the place on the galvanic scale which determines what fails first, but also the relative size of the components. So, for example, ss fasteners are ok for bronze (talking generically) fittings, but it not a good idea to use bronze fasteners for ss fittings. So, one would expect in the stem band case mentioned for the bronze to fail first.

You will find that a search of the internet will turn up various fastener/fitting compatability in seawater tables and you will find that while fastenings of one metal for use in another metal will be ok, if you reverse the metals between the fastener and the fitting, then it is not ok - has to do with the relative size of the metals in the fastener/fitting system.

John

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