60007 (4498) Sir Nigel Gresley Overhaul

What a luxurious workshop...

 

Looking at 4498's move to Crewe. It's a case of "full circle" as when the A4 Society [or what ever they were called back then] bought the loco, they had her overhauled under contract there.

 

First update from Crewe, where dis-assembly to move towards full completion seems to be the order of the day.

The 'Sir Nigel Gresley' Locomotive Trust Ltd

 

Many thanks as usual...

 

Another update has appeared, as the 1001 jobs to finish are ticked off.

The 'Sir Nigel Gresley' Locomotive Trust Ltd

 

Picture here shows the successful pressure test on the last of the three main steam pipes, now signed off, they will be fitted in the smokebox later this week after which the front can be reassembled for the last time before the return to traffic.

 

Thanks for the update much appreciated...

 

What you would expect to be the last update of 2021 has appeared, great progress continues to be made.

The 'Sir Nigel Gresley' Locomotive Trust Ltd

 

Thanks for sharing. 2022 should be good!

 

Wouldn't want to be the person wear the orange hi-vis if the pipe blew!

Sent from my SM-J330FN using Tapatalk

 

I was thinking exactly the same thing...

Richard.

 

It's not a steam test.

 

An hydraulic test ..it seems to me? A hydraulic pipe burst can still cause death..

 

There should be no air trapped in the pipes so very little energy and very little water ejected, if any. That’s the whole purpose of a hydraulic test; it should be safe.

 

I am quite sure these guys know what they are doing, and if any danger or problems could ensue, the pipes would be taken to a "expert", for testing and certification. With LSL's help, they have excellent workshop and backup facilities, part of the reason for the move.

 

You seem to be confusing the issue. An air lock which I think are referring too, you seem to state that it affects the energy?

 

Yes. AIUI, in the limiting cases at either end: If the system was perfectly full of water with no air at all, then if there was a sudden rupture, the water inside would go from high pressure to ambient with a negligible change on volume, so no real impact or release of energy (released as e.g. a jet of fast-moving water).

At the other end, if the system was full of air at high pressure with no water, a rupture would be catastrophic as there would be a huge increase in volume as the air pressure went from high to ambient.

In the middle, with a hydraulic test but with an air lock that has trapped some air, a rupture would still be damaging as the volume of trapped air would expand and either directly vent, or (depending where the rupture was), force out a jet of high pressure water until the pressure had dissipated.

Tom

 

Liquids are usually thought of as being incompressible. They can be compressed but it takes a great deal of energy and you achieve very little compression so for all intents and purposes they are considered incompressible.

So with a hydrostatic test the smallest defect has a noticeable effect on the pressure reading, first pit to pass the failure post on a tube for example; this is assuming that the vessel that you are testing can be viewed as being essentially rigid for the purpose of the test. The problem arises when this is not the case.

Having a 4" or larger SAE300 flanged hose tail launch itself out of an industrial rubber hose while an assembly is under a 30 bar test is not the same as testing a steel main steam pipe. The hose can stretch, the length can extend under test for metres, the bore expands too, the products of some manufacturers are very poor in this regard. Other manufactures can produce a product which is close to indestructible, if you are producing hoses to convey hydrogen cyanide for example, these have a very high safety factor and samples of a batch are destructively tested under independent observation. But sometimes the test pressures reached are so high that the destruction point is not reached and the test is concluded. Just too much pressure trying to escape confinement from a vessel which is not rigid.

So if your vessel under test can be viewed as rigid you should be safe with an elastic vessel you need to be more careful.

 

I don't think I'm confused. I've carried out plenty of hydraulic tests in my time. The whole principle is to eliminate the air and reduce the potential energy to a negligible amount. You can tell if there is air in the vessel when you pump it up.

 

Like

Car brakes for instance I get that. I too have carried out hydraulic tests on occasions. Having a gas/air in a system will give you a false impression. No criticism by the way, just observation...I don't consider myself infallible by all means..