Pendolinos ordered for Poland

[Peter Mugridge]

I think it's the aluminium ( see the QE2 forum for details; QE2 has a steel hull with an aluminium superstructure on top and there are threads over there about it ).

 

[Nym]

Ahhh, but that will be something to do with it being submerged in salt water as well one would assume (the reason why ships normally have sacrifical zinc bars)

 

[Peter Mugridge]

Yes, the high salt environment is not exactly the frendliest one in which to operate!


Seriously, though, the grit used on roads and on platforms does have enough salt in it to cause problems so logic suggests taking full precautions is well worth it. They announced on the BBC local news tonight that it is the salt from road grit which has caused the problem with the Hammersmith flyover and the pictures shown of the steel rods in it were not very pretty ).

Don't remember mention of a zinc bar in the QE2's transition joint though; I'll have to locate the thread and read it through again, then ask if there is no mention of it ( thread grave digging is encouraged on that forum so that won't be a problem ).

 

[Nym]

It was used on iron ships, because something to do with electron flow or something, they shove a bar of zinc on and that corrodes instead of the iron, and takes all the corrosion. (Not touched this topic since A level chemistry, and that was a looonnnggg time ago)

 

[ChrisCooper]

It's the Aluminium that suffers. Aluminium is more electronegative (attracts electrons), than Iron, so will form an anode in the electrochemical rusting reaction and turn to Aluminium Oxide (oxidation is a gain of electrons), a white powder. It actually helps protect the steel and will reduce any rust (iron oxide). To protect the aluminium it either needs to be insulated from the steel (as there is a tranfer of electrons, an electric current), or another more electronegative element (magnesium) needs to be provided which will give up electrons to the aluminium to stop it oxidising. Aluminium is often used as a sacrificial anode to protect iron and steel.

I'm in the process of restoring a 1978 Northern Counties bodied Leyland Fleetline. Northern Counties used Aluminium Panels on a Steel Frame and Steel Chassis. Naturally the panels suffer badly from corrosion around where they contact the frame. Had to replace almost the whole lot. Doesn't tend to help the frame though as they corrode badly in places too.

 

[dubscottie]

Mk4s are made from aluminium extrusions.

To be honest I don't get all this "i'd rarther be on x train than y in an accident. I'd rarther not be in a train crash at all, and if I'm going to be in a serious one then my chances of walking away or not seem to be more down to luck than anything else (afterall if doesn't matter if 1 or 100 people are killed in an accident if you or someone you care about is one of them).

Mk4's are STEEL based around the bodyshell of the Class 156's. The first UK trains to use aluminium extrusions were the class 158's

 

[HSTEd]

It is possible to prevent the electrolytic corrosion though, some more modern vessels, especially military ones (the idiotically badly designed Littoral Combat Ships most famously) by forcing a reverse potential across the "electrolytic cell" which prevents current flowing which prevents the corrosion from occuring.

Many of these only do this while attached to the dockside power supply though.

 

[ainsworth74]

especially military ones (the idiotically badly designed Littoral Combat Ships most famously) by forcing a reverse potential across the "electrolytic cell" which prevents current flowing which prevents the corrosion from occuring

God help those ships when they encounter real weather for the first time, a 50kn top speed isn't going to be good for much in the middle of this: