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Dissimilar metal corrosion on highway signs.

Dissimilar metal corrosion on highway signs.

Dissimilar metal corrosion on highway signs.

(OP)
We are refurbishing (in UK ) old highway signs - - 40 years old Cast iron arms with collars supported them from Mild steel columns. Generally  at the interface the MS pole is  seriously
corroded due to rain getting between the dissimilar metals. There is a very small differential between these two metals.

What staggers me is  that in the UK the present motorway construction is for galvanised  MS columns with the message board affixed by numerous Stainless steel bands.
 Stainless and Galvanised metals are hugely different .
 With the increase  of acid rain I would imagine serious         problems in near future.

Please has anyone any comments.?

We also find that generally, the 40 years old MS  poles are still 100% original thickness where they have been buried, but then  at ground level they instantly are corroded , sometimes zero metal left.

I have been told it is a well know phenomena. Please have you any comments ?

Thanks in advance.
ground level.       

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