Galvanic corrosion

[darren bastin]

Wondered if anybody could offer some advice. I have to join onto some steel central heating pipes, i was planning to to do this with standard brass threaded fittings and then off I go on copper pipes. It has been pointed out to me that this will cause problems with corrosion in the future. I dont like using plastic if i can avoid it, i assume the corrosion occurs at the fitting and not on the pipe itself ? Are there any alternatives ? What measures could I employ

 

[AWheating]

if the steel does not touch the copper then you should be fine.

 

[darren bastin]

if the steel does not touch the copper then you should be fine.

I would use a male inch to 22mm soldered fitting to connect directly into a steel inch t. Would the brass fitting not corrode ? Should I use a plastic fitting to seperate the metals?

 

[Nostrum]

How do you normally connect steel radiators to copper?

 

[Mike Jackson]

Is this not what corrosion inhibitor was invented for?

 

[rawr]

is it not electrolytic action?

 

[lame plumber]

if the steel does not touch the copper then you should be fine.

the whole problem with corrosion by dissimilar metals is that the corrosion occurs through electrolytic action and the higher up the galvanic scale a metal is the easier it will corrode, hence why brass d bronze etc corrodes where steel is present, and there's no better place for this to be seen than ships propellers rotting in sea water where because of the additional salt the reaction works quicker. Hence ships and some water vessels have sacrificial anodes that corrode getter than the bronze props which are then protected. Same in a heating system where it would be best to have no dissimilar metals but all of one metal, impractical, so keeping impurities (flux) out of the heating water and use of inhibitors will prolong the life of the system, but physics will always win in the end and corrosion will win!

 

[AWheating]

the whole problem with corrosion by dissimilar metals is that the corrosion occurs through electrolytic action and the higher up the galvanic scale a metal is the easier it will corrode, hence why brass d bronze etc corrodes where steel is present, and there's no better place for this to be seen than ships propellers rotting in sea water where because of the additional salt the reaction works quicker. Hence ships and some water vessels have sacrificial anodes that corrode getter than the bronze props which are then protected. Same in a heating system where it would be best to have no dissimilar metals but all of one metal, impractical, so keeping impurities (flux) out of the heating water and use of inhibitors will prolong the life of the system, but physics will always win in the end and corrosion will win!

wiki is very helpful

 

[dancinplumba]

if all parts in a heating system were made of plastics, then there would be no problem

 

[AWheating]

quality brass is better to use than copper as the gap on the "thingy" scale is less, if the system water is clean/fresh then its normally a weak electrolite (spelling?) so you will not have a problem.

think about it, normal heating system is a mix of copper pipes, brass fittings and steel/iron rads and boiler parts.