Pending paint warranty claim against Hitachi…?

[Peter Mugridge]

The length of the vehicles doesn't make any difference, - they are cleared for the routes that they use.

With regard to fixed structures, but vegetation will often invade the kinematic envelope.

Yes. Just for the science Al is -1.67 volts with respect to Hydrogen potential (assigned 0 by convention). Fe is -0.44 volts. So a driving voltage of 1.23 volts which is quite high. A bimetallic couple (galvanic corrosion) with corrosion almost designed into the system. Sure, you can get paint to adhere to metals - but not to corrosion products. Zinc and Aluminium are notoriously difficult. In the aircraft industry, they have to use Strontium Chromate pigment.

This thread on the QE2 forum may be of interest:

Steel/Aluminium Transition Joint & repairs/patches to the superstructure

Steel/Aluminium Transition Joint & repairs/patches to the superstructure

www.theqe2story.com

There's several posts on that thread which would relate to the question of galvanic corrosion as being discussed here as well.

One I have partly quoted below demonstrates how careful you have to be to ensure that noting at all can bypass the measures put into place to prevent such corrosion from taking place, and it's easier to invalidate the protection than you might think:

In 2003 I spent a year as QA manager in a shipyard that manufactured superyachts (or tried to - they never ever got it right!), often with high-strength steel hulls and alloy superstructures. The 'Bang Stick' strips we used to insulate the steel from the alloy were manufactured in Belgium by using explosives to bond a strip of alloy to a strip of steel. By totally bonding the grain structure of the two materials, electrical galvanic action was greatly reduced between the two materials. Until some silly twerp would ignore the instructions on the build drawings and install a pipe incorrectly (or use a pipe of the wrong material), thus giving an electrical path which would totally defeat the insulating properties of the 'Bang Stick'. Or incorrectly weld in a new access ladder and totally negate the "Bang Stick by giving a new path to the electrolosis.

 

[AM9]

With regard to fixed structures, but vegetation will often invade the kinematic envelope.

To enable the 8xxs to pass what is essentially the same route, they have their bogies inset by over 2m and the end doors are nearly over the outside axle. Indeed, the bogie centres are probably very similar. To compensate and prevent the carriage ends extending beyond the kinetic gauge, the ends of the cars are tapered beyond the doors.
But the HSTs had cars that were only 3m shorter. On the MKIIIs the door is right at the end of the main body so in effect slightly more exposed.

So I think that both types are likely to get similar thrashings from the undergrowth.

 

[O L Leigh]

… not to mention nightly flagellation courtesy of the wash plant which administers quite a beating.

 

[GRALISTAIR]

… not to mention nightly flagellation courtesy of the wash plant which administers quite a beating.

True but cars endure brutal winters and deicing salts and car washes - and my wife's car here in the US paint job is fantastic and it is 10 years old and nearly 100,000 on the clock.

 

[O L Leigh]

True but cars endure brutal winters and deicing salts and car washes - and my wife's car here in the US paint job is fantastic and it is 10 years old and nearly 100,000 on the clock.

That’s good, but is it a steel body or an aluminium one? I’m assuming that Her Ladyship isn’t driving it daily through the car wash. If the racket that a train washer generates is anything to go by, they are a degree or two more rigorous than any car wash I’ve ever used.

I would imagine that car manufacturers are better at getting the paint stage right, especially given the potential costs of putting it all right afterwards. They are also shifting units in the hundreds of thousands, so a few with defective paint won’t attract much attention.

 

[northernbelle]

Yes. Just for the science Al is -1.67 volts with respect to Hydrogen potential (assigned 0 by convention). Fe is -0.44 volts. So a driving voltage of 1.23 volts which is quite high. A bimetallic couple (galvanic corrosion) with corrosion almost designed into the system. Sure, you can get paint to adhere to metals - but not to corrosion products. Zinc and Aluminium are notoriously difficult. In the aircraft industry, they have to use Strontium Chromate pigment.


I will reserve judgement, but I tend to agree with you.

What makes me suspicious is that the bubbling of paint appears to be occuring in similar locations across all vehicles, and on vehicles manufactured at different plants.

All the common locations for bubbling paint appear to be areas where the aluminium bodywork might interact with other fittings or framework - door pockets, weld lines, where window glazing is fixed in and where there are steel fixings such as the headlight surrounds or external door egress handles.