Fresh Water Corrosion

[ssm23671100]

I have a narrow boat on the canal system in the UK it is only four years old and some of the 10mm bottom plates are badly corroded,and one of the plates welded to the others is fine,as it is flat bottomed they are all at the same depth.I have had metallergy tests done, the only differance is in the manganese content, on the bad plate it is 0.51%,and on the good plate 1.08% would this account for the corrosion.

 

[MikeHalloran]

Which one is nearer the zincs?



Mike Halloran
Pembroke Pines, FL, USA

 

[ssm23671100]

The anodes are level with the weid between the good and bad plates.Thanks for the return cheers.del

 

[TCAir]

Really rough guess here but are you loosing electrical current into the boat? Maybe a bad bilge pump wire.

I know that can do it quick, just something to check.

Engineering has always been my love, but it ended up being my second career...

 

[waross]

I would be immersing a sample of each plate in some electrolyte (salty water would do) and checking them with a voltmeter. If there is any voltage at all between them they may be considered dissimilar metals and they will develop a potential difference or voltage in service. This potential difference will cause a current to flow from one plate to the other through the water and complete the circuit through the welded joint between the plates. My guess is that the manganese rich plate is acting as a sacrificial anode and protecting the rest of the boat.

Bill
--------------------
"Why not the best?"
Jimmy Carter