A nail in the coffin for mainline steam?

[jamie92208]

I've just read through the report and it does seem very fair and balanced.  The consequences of the connecting rod digging into the ballast could have been horendous.  I was living at Settle at the time of that accident.  That also happenned on an embankment and it was lucky that neither train went down.  All in all everyone seems to have been very lucky but some important learning points have emerged.  The question of changing standards during the lengthy restoration process is one that i came across with the horse tram that I helped to restore and it is a difficult one to deal with.  

 

Jamie

[PenrithBeacon]

I've just read through the report and it does seem very fair and balanced.  ... Teh question of changing standards during the lengthy restoration process is one that i came across with teh horse tram that I helped to restore and it is a difficult one to deal with.  

 

Jamie

Yes! Another issue is that there are people out there who feel they know better than their forbears. This is not just restricted to putting engines in 'funny' liveries but can and does involve redesigning parts of the engine as touched on in the report. Not a great idea, best to be conservative (note the small 'c').

 

Regards

[jamie92208]

Yes! Another issue is that there are people out there who feel they know better than their forbears. This is not just restricted to putting engines in 'funny' liveries but can and does involve redesigning parts of the engine as touched on in the report. Not a great idea, best to be conservative (note the small 'c').

 

Regards

Sometimes there is no information about the design of detail parts and new ones have to be designed and manufactured from scratch.  The lesson I learned was to keep a design log of each such part detailing the source material, decision making process and the method of manufacture.  This should then proove that reasonable care had been taken in the process.  I was very grateful to have that file of documents relating to all the safety critical parts when we had an incident and the RAIB and HMRI came to call.   Fortunately for railway locos a large number of original drawings still exist.

 

Jamie

[PhilH]

 

 

Fortunately for railway locos a large number of original drawings still exist.

 

yep they do...drawing for gudgeon pin and crosshead for Bulleids.

 

[PaulRhB]

A castellated nut would seem like a good idea and proved to be on many other engines, the only thing they seem to have missed is the potential for more movement because the threads were different. I doubt many would think of that if they looked at it without actually knowing it was an issue and actually checking what thread it was. Another issue with drawings is have you found the last one they did? It's an issue we come across regularly in models where modifications were made later and the only surviving drawing is older. In this case it appears this drawing is the latest one but it's another trap you can easily fall into on any engineering or electrical job. I know we struggle to find the latest drawings for current installations

[MarkC]

I'm inclined towards the castellated nut fracturing, due to the slots not being rounded at the bottom. This meant that there were stress concentrations there. (Original Comet aircraft windows...). Sadly the nut was never found, but it does seem most likely

[roythebus]

We, like the RAIB, can speculate for ever on what the actual cause was. The fact that the case in itself is an extreme rarity is testimony to the railway safety record. Once every 60 years.

[PhilH]

Exactly...one thing that did strike me on re-reading the report is that there is an awful lot of supposition and speculation in it, enough to make it near worthless really.

[PaulRhB]

Well we know the nut was there with cotter at Waterloo so that nut came off somehow. The circumstantial evidence that only the nut and cotter went missing says its one of those two that failed. From that a simple metal fatigue failure of the nut would be down to a poor piece of steel or some flaw introduced during manufacture or service, without the nut it's impossible to tell but it's less likely than the smaller cotter failing. So they look at the cotter and the report identifies a couple of reasons the nut might cause the pin to fail or the pin design itself. The sharp edges on the castellation are a good point and combined with the thread make a good case for a stress fracture on the smallest and weakest component. If all three possible design flaws are modified you put the likelyhood of the pin failing into the same accidental chance area as the nut. The position of the pin being vertical is just belt and braces.

I'd say their recommendations are sound engineering experience of fatigue failure and certainly reduce the risk. What other option is there than ban that type of loco because it has no secondary system to catch a unsecured rod, unless they start adding some form of safety strap which would be more of a liability in normal use.

As Phil said the main pin itself should be pretty secure and may have been for miles before the clanking started, we just don't know what caused it to come out, so their conclusions cover the tapers and found no flaw there.

Luck meant it happened at lower speed and the third rail caught the rod, if it had happened like the earlier incident at Settle then we'd be possibly looking at what would happen to mk1's in a crash which already run under dispensation plus any other trains involved. Clapham showed what is possible there and that's a bit close to home too in this. Also consider what the effect of a heavy diesel on the back does, the loco doesn't brake as well as the coaches and you frequently see the buffers slightly compressed at a stop so if the loco on the front stops suddenly you get a similar effect to what happened in Spain causing coaches to concertina sideways and then all he'll breaks loose.

A few sensible engineering conclusions plus as Phil said don't change the design that works is better than the consequence of a fatal accident with consequences probably banning mk1's really makes mainline steam hard to do.

[Titan]

Another issue with drawings is have you found the last one they did? It's an issue we come across regularly in models where modifications were made later and the only surviving drawing is older. In this case it appears this drawing is the latest one but it's another trap you can easily fall into on any engineering or electrical job. I know we struggle to find the latest drawings for current installations

 Interesting you should make that point, the drawing above is not correct for a West Country Class, as it has a one piece piston rod/cross head forging. the correct drawing is reproduced on page 15 of the RAIB report.

[The Stationmaster]

Exactly...one thing that did strike me on re-reading the report is that there is an awful lot of supposition and speculation in it, enough to make it near worthless really.

Agree Phil - regrettably the lack of evidence from the lost parts does tend to lead to that.  While I do not argue with the conclusions and recommendations (by RAIB standards it seems a very good report from a quick read) I'm surprised they did not look more searchingly into not only the modification but also the specification & quality of materials used (in view of previous comment from them on the latter point in relation to an incident on the SVR).

 

However the point was well made that you shouldn't embark lightly on any course of modification to established engineering standards on steam engines - especially so to those operating on mainlines - where Paul has made a very pertinent point about diesels locos attached trailing.

[Gwiwer]

I'm not an engineer but the RAIB has access to, or maybe has within it ranks, among the best railway engineers there are.  They are also well versed in researching right down. literally, to nuts and bolts, every tiny piece of evidence in an investigation.

 

There are also engineers and seasoned men of steam among our number and I defer to their vastly superior subject knowledge.  But I feel the report is as precise as it reasonably can be given that some critical pieces of the jigsaw are missing and are unlikely to ever be found.

 

Yes we are extremely lucky that the incident happened at a moderately slow speed and that the rod didn't dig in.  We are lucky that a historic locomotive wasn't forced down the embankment leading its train to catastrophe.  The relative risk of conveying a dead-weight diesel on the back must have been assessed long ago before such formations were accepted on the main line.  The loco is 100-plus tonnes of metal but was not powering - had it been under any sort of power the event might have ended differently.

 

But the facts remain that no-one was hurt, the train remained on the tracks, there was relatively little damage to loco or infrastructure and perhaps the biggest losers were SWT's heavily delayed fare-paying passengers.  Once in 60 years is once to often but given that for some of that time steam was the major form of motive power and that apart from a few years has been active on the main line ever since suggests that - statistically - the chances of a repeat are extremely small.

 

To compare the incident with Clapham Junction is perhaps emotive.  Yes it was on the same route and very similar rolling stock (Mk1) was involved but Clapham was caused not by a train fault but by signalling failure and it was pure mischance that the third train happened to be so close to the first two that it became involved.  If we must draw parallels then perhaps a more suitable one might be the impact of two trains at Stoats Nest on the Brighton main line in which part of a Littlehampton - Victoria train was pushed over the edge of the embankment ending up in private gardens below and with five (six in some reports - I believe a sixth person, who survived the impact, did not survive their injuries) fatalities.

[PhilH]

Interesting you should make that point, the drawing above is not correct for a West Country Class, as it has a one piece piston rod/cross head forging. the correct drawing is reproduced on page 15 of the RAIB report.

..but the gudgeon pin drawing is from W11335 (as posted above) thus adding(?) to the mix....

 

Time and tide move on and steam engines out on the mainline today are in places virtually unrecognisable from the locos in BR or constituent company days. Huge mods to braking systems, enough electronics to send a man to the moon (well, almost) mean that original design concepts through necessity often have to be modified. Plus, of course, some modern day techniques and even materials are often seen as an improvement over those of 50+ years ago.

 

Mods are not just carried out willy nilly, they are thought through and have to be approved by regulatory bodies - as has been pointed out the fact that this has been the first event of its kind for 60 years would seem to suggest that the present approach is about right.

[Steven B]

Yes! Another issue is that there are people out there who feel they know better than their forbears.

 

If people only knew what their forbears knew then Tangmere would look like this and Duke of Gloucester would be razor blades.

 

Happy modelling.

 

Steven B

[ozzyo]

yep they do...drawing for gudgeon pin and crosshead for Bulleids.

 

W11335 Crosshead (Outside).jpg

 

A very interesting drawing,

 

The first part is it's for a loco with out side vale gear, and of the new two piece type cross-head.

 

The small end pin is only held in place by two things, the fit of the taper (normal 1:20) and the out side nut. With a parallel key, to lock the nut in place. the part that helps it all to work is the shim washer that is behind the nut (made a few of them in my time). Get the nut up tight, measure the gap and then add a few thou. Bingo. 

 

The hardest part of machining one of these small end pins is allowing for the cut off on one end of the taper. between the cross-head.

 

I did have a long talk about how a piston rod should fit into a cross-head one day,  but what the hell the loco runs!

 

OzzyO. 

[jjb1970]

The RAIB report seems pretty well found to me. Most reports are based on a degree of conjecture as the events have generally to be reconstructed from fragments of evidence and by its very nature the process leaves a degree of uncertainty. Ultimately it requires a degree of trust in the judgement, experience and capability of the investigators and the fact so many incidents result in long running disputes and generate alternative theories and conspiracy theories is itself an indication that accident investigation is an imperfect science. This may sound odd but in many cases establishing the exact circumstances of what went wrong is not always that important as most accidents are the result of a series of failures (google the swiss cheese model of failures) and the learning points resulting from investigating the various identified failures are of huge value even if there is a degree of uncertainty over the sequence of events. 

On this, it is certainly true that management of change is a critical aspect of engineering safety. In my experience it is the small things that cause disasters. If you were to change a big ticket item from original design (like an engine control unit on a modern prime mover) you'd do a full analysis of the change and it'd be properly risk assessed. The problems generally are when you get small low value items that are no longer available so people do a like-for-not-quite-like change without doing this full analysis and it ends up in a disaster. 

[PaulRhB]

To compare the incident with Clapham Junction is perhaps emotive. Yes it was on the same route and very similar rolling stock (Mk1) was involved but Clapham was caused not by a train fault but by signalling failure and it was pure mischance that the third train happened to be so close to the first two that it became involved.

I chose that parallel because of the stock parentage and the consequence of a rear impact, in this case the momentum of the diesel, adding to the problem. The fact it was on the same line would just have been a nasty coincidence. Retro fitted cones would help if all the force is in line but IF the loco had detailed then it may pull coaches sideways and even modern coaches suffer as Ufton and the Spanish Talgo accidents show.

The root cause is indeed different but the situation the train is then in could have been very similar. Considering the amount of supposition they had to use it actually looks at a broad range of factors that will hopefully mean they avert the chance of human factors causing a similar occurrence. There's little we can do about hidden flaws without stripping down and testing all parts even more regularly which would kill any TOC let alone steam's chances of being viable.

[jjb1970]

One problem with high profile accidents which generate media interest is that it complicates investigation hugely as it often ends up with the media, pressure groups etc peddling theories that are considered unlikely at best (and in some cases absurd) by those doing the investigation but politically a lot of effort ends up being spent addressing these ideas. Often to no avail as when the investigators present their case to explain why it is unlikely it often ends up just being held up as some sort of vindication and evidence of conspiracies at work to hide the truth. I know some chaps who were involved with the various investigations into the loss of the bulk carrier Derbyshire over many years who are still pretty beat up over the way that they were attacked in some really quite vicious and personal ways by those peddling ideas which were questionable at best. One structural engineer I know was being tailed by people who were turning up at meetings to heckle him on account of not liking some work he did on the hull structure.

[roythebus]

A bit like the "fit seat belts to all trains" after the Ufton incident!

 

At the moment my son is involved in an inquiry as to why a 171 gudgeon pin failed recently. Luckily it only blew the engine to pieces and probably caused some delays. I've seen the pictures but can't publish them, but there's quite a big internal inquiry as to why the pin failed.

 

So it's not only steam that breaks!

[jamie92208]

A bit like the "fit seat belts to all trains" after the Ufton incident!

 

At the moment my son is involved in an inquiry as to why a 171 gudgeon pin failed recently. Luckily it only blew the engine to pieces and probably caused some delays. I've seen the pictures but can't publish them, but there's quite a big internal inquiry as to why the pin failed.

 

So it's not only steam that breaks!

Don't Deltics have a reputation for 'Putting a leg out of bed' as well.

 

Jamie

[Gwiwer]

Don't Deltics have a reputation for 'Putting a leg out of bed' as well.

 

Jamie

 

"Putting a leg out of bed" in diesel terminology usually refers to a failure within the piston and cylinder which causes the piston to emerge where it should not do at one end or other of the cylinder or indeed though its casing.  It's possible that could be caused by a gudgeon pin failure; it could also be caused by catastrophic failure of the cylinder block casting.

[Richard E]

And in motorsport 'putting a leg out of bed' is a term associated with a con rod appearing outside the block, usually the side, due a rod breakage or a failure of big or little end and/or their fastenings. It may involve the piston, or bits of it, also appearing. The best I have seen wrote off block, crank and front cover; there were some of the ancilliaries that were salvageable but the alternator was never found. The reason for retirement was given, euphemistically, as alternator failure.

[New Haven Neil]

I once saw a large (25cm ish bore 8 cylinder in-line) Ruston ships generator engine put a leg out of the bed due to a governor failure and subsequent overspeed....a more frightening thing is hard to imagine.  The crankcase was 'metalok stitched' back together by specialists, the piston was shattered, and the rod bent like plasticene.

 

Oh, and yes, it made a very, very loud bang!

[MarkC]

That one could have been worse, Neil - like the flywheel going walkabout...

[New Haven Neil]

Yep, the 3rd was at that end when she went, the opposite end to the governor.....eek.