Flying Scotsman

You are right of course, but we are not discussing the finer points of metal fatigue. In #6098 it was simply stated that age did not matter to which I gave examples where it did. I should also have mentioned "creep" which can exist in hot stressed parts. Please note that all
the examples I mentioned can be prevented. Intercrystalline corrosion can exist in "polluted"steel, fatigue can be designed away by proper dimensioning and creep can be kept under control by materials choice/metal chemistry.
I am probably oversimplifying and forgetting others possibilities.
Kind regards
Jos Koopmans

 

I think that there is a need to keep it simple as it is not a true technical forum but there is then the danger that we end up not being totally correct in what we say. It's a fine line.
Our locos are getting older but, because they generally do a relatively small mileage, their 'operational age' is, in many cases, not great. Most BR standard locos would probably have an operational age equivalent to about 20-25 years of BR service, which isn't old for a steam loco. There are exceptions, of course!

 

Re "fatigue can be designed away", I think that is slightly misleading, as machines are generally designed for a finite life, both for economic reasons (e.g. not being unnecessarily massive) and on the basis that technology changes (it is likely to be replaced by improved technology before too long). Thus aircraft are designed for a number of cycles (which for aircraft like the 737 often gets extended based on practical experience (whereas a lot of 747s will run out of economic applications before they start cracking too badly)), not to last forever, and ship hulls I believe are designed to sail through 10 to the power of n waves, where l0 to the n is quite a large number. I am not sure that steam loco design was considered in those terms, but clearly it is a factor to be taken into account, normally by replacing components, or management of cracks.

 

As usual, @Steve covers it succinctly and I'm going to waffle on.

Steel is a lovely forgiving material, that if well protected and moderately loaded, will indeed go on effectively forever. The stress at which this desirable state of affairs occurs for a given alloy is often known as the 'endurance limit'; some newer publications question whether it truly does exist, but for most practical purposes it's good enough. Above that stress, we live in the realms of S-N curves, where S is the magnitude of stress fluctuation (corrected for average static stress) and N is the (statistical mean) number of cycles you'll get before failure. It may be preferable to design in this regime if lightness matters above all else, or the component has a functionally limited lifetime anyway.

Titanium alloys behave in a similar manner to steels, but most other metals don't; the S-N curve goes all the way to the end. They will fail eventually if cycled often enough, no matter how low the load, so any structurally significant component in (for instance) aluminium alloy has a maximum permitted number of stress cycles, based on the design load case.

High cycle fatigue failures behave a lot more like brittle fracture than ductile, which is why there used to be a lot of waffle about the material crystallising due to age, and parts where fatigue life is the limiting factor almost have to be designed as though from brittle materials; large inside corner radii and compressive stresses in the surface are helpful (like toughened glass). Various features require adjustment to the S-N curve or endurance limit during design.

Welds have a negative effect on fatigue life, which is why simply grinding out a fatigue crack and welding it up will lead to a recurrence of the crack in a much shorter timescale than it took to originally emerge. In the case of cracked main frames (see, almost relevant to Flying Scotsman), cutting out a large portion and inserting new material with the weld well away from the crack in a lower stress region is the only practical long term solution.

On a completely different note, a non-railway enthusiast friend of mine mentioned seeing Scotsman on one of her recent mainline outings. No comment was passed regarding its appearance (livery, smoke deflectors, number, whatever) at all, but he found the feeble whistle rather incongruous.

 

All this talk on metal has just reminded me of bolts that had heads made smaller to save metal during WW2.Just for example a whitworth thread three quarter of a inch bolt had a head brought down to a pre war eleven sixteenths bolt head (I think that was the size ,long time ago ).No big deal, but it was a bit of a nuisance when the wrong size was spanner came out .What size heads do they make now ?.All metric I expect.

 

Coming back to Scotsman for a moment, the increase in boiler pressure and keeping the A3 cylinders - thereby generating more cylinder horsepower - certainly gave some excellent performances but... from my limited understanding of stress, the stress cycles would have been higher whilst the engine was in this condition and therefore possibly leading to some of the damage, or worsening existing damage in the frames and motion. Sorry about that boring bit - back to Volvos and Lightnings.

Mike

 

It depends how much time was spent producing more thrust than would have been available with standard A3 parts. Maximum effort hill climbing and maximum acceleration from stops wouldn't be a major part of the total time run, though it might have been a significant fraction. I recall reading of a max effort over the Devon banks which must have been well over normal A3 performance.

 

At least with good ol' Whitworth you had consistency with spanner sizes. Not so with metric where there is quite a bit of variation. For example, for an M10 nut, the standard spanner is 17mm but the Germans use 16mm, the Japanese 14mm and the Americans 15mm, as you'll find if you own cars from these places. Spanner sizes required for M8, M12, M16 & M20 also vary depending on country of origin. To cater for the full range of possibilities between M6 & M20 you need 14 different spanner sizes whereas the equivalent 1/4" BSW up to 3/4" BSW only requires 8.

 

Blimey ,what the weight of a tool box these days with all those spanners in. Some fitters tools box needed a crane to lift them in the 1950/60s dread to think what's it like now.

 

Our toolboxes at work have wheels on them! Working on various EMUs - 313s, 317s, 319s, 321s and 365s - means a lot of tools. 0BA, 2BA, a few imperial spanners for pipes etc, plus metric spanners from 4mm to 41mm are all regularly used. Plus sockets. Now do you want them in 1/4" drive, 1/2", 3'8", 1".....! Plus adjustable spanners of various lengths as some of the nuts and bolts seem to have been individually handmade to random sizes!

 

That's why adjustable spanners came to the fore. In my young day these were very much frowned upon, especially the traditional English version. The advent of the Bacho adjustable did make them a lot more respectable although the cheap replicas that you can buy on market stalls really should be banned..

 

I'm very much an 'old school' Chief Engineer when it comes to the wretched things being permitted in my Engine Room, Steve - even Bahcos. They're not allowed. Blanket bans avoid confusion - or my having to explain the difference between a Bahco and cheapo Chinese rubbish to my staff... I hate the things, as used inappropriately they can cause so many more problems than their perceived benefits. Pardon the expression, but rounded nuts are a nightmare... as are rounded off valve stems on refrigeration system isolating valves...

 

Thanks for the remarks. Never heard of a Bahco .But if the adjustable are the type I'm thinking of there wasn't a great lot of space in a loco smokebox to manoeuvre one on the steam pipes bolts /nuts .The jaws on a adjustable were to big. Not a nice job in any case,nuts were on so tight they quite often needed" cracking " (nearly cut in half )with a hammer an chisel.

 

You've missed the most important............................a large lump hammer.

 

Bahco is a Swedish firm which invented the modern adjustable spanner (amongst other things.) Never bettered, often copied, IMHO. Go to any tool shop and look for the most expensive adjustable. However, as MarkinDurham says, even they are no substitute for a properly fitting good quality open-ended spanner.
Chiselling off nuts seems like hard work. A good dose of 'warmalene' usually does the trick much more easily. If only we could have used it down the mine......

 

It was said in my branch of the motor trade that the most important difference between an amateur and a professional mechanic is that the professional knows which hammer to use and how hard.

 

Molegrips.......aaaaaaaaaaaah.

 

I too am an adjustable spanner hater. I spend a lot of time working on Landrovers which frustratingly often come with pre-ruined nuts and bolts necessitating the need for the heat/clamp on mole grips/beat with hammer/more heat/more beating technique.
The above adjustable (it's next to a 19mm for scale) recently got given to me, and it's a beaut, actually fits stuff properly and doesn't rattle loose! Don't get me wrong it's not a ring spanner....but it has already saved a bit of a headache on a 'mystery bolt' on a mates trailer!

Chris

 

I'm not sure that I agree with this point. Whenever FS is on full regulator, more or less full boiler pressure will be applied to the pistons, and this force will be transmitted through the rods, bearings etc. and back though the frames. I would think this would apply to most of the LNER pacifics for a fair amount of the time.

I wouldn't like to get into an argument about the Thompson pacifics though .

 

I use to annoy my Mum by taking stiff tops of bottles with a Stillson wrench.