Boiler approval and testing

Hello

I have recently seen references to the MELG model engineers boiler test code AKA the blue book.

Is this document freely available or is its issue restricted to Club Boiler Inspectors? If it is generally available can some kind soul point me in the direction of a source?

I am not a club member but would like sight of it to see what standards are expected before I commit myself to building a Tich boiler.

Thanks

Dave

Volume 1 (>3bar litres)

Volume 2 (<3bar litres)

Your 'Tich' boiler will conform as drawn provided that you use boiler bushes for all attachments and fittings rather than screwing directly into the copper structure as LBSC occasionally advocated originally.

Phil

Edited By Weary on 08/07/2022 19:28:00

Hi Phil

Many thanks for your prompt and thorough reply!

Cheers

Dave

Actually not technically true as the 'grandfather rights' that allow your boiler design to be accepted without calculations only apply if built to original drawings but any boiler inspector with an ounce of common sense will agree that it is better to bush fittings rather than tap the boiler itself.

Ah but, the OPs boiler isn't exactly as LBSC, as others point out the bottom fitting for the gauge glass is way too low. The boiler inspector might accept some kind of shroud as others have suggested, but I'd want a good look at it to make sure the staying etc hasn't been altered. I've got the Tich drawings which were given away as a freeby with ME some time ago, if the OP wants a copy just send me an email address via pm

Hi Duncan

I haven’t built the boiler yet! You have mixed my op with another.

I’m fully aware of the consequences of exposing the firebox crown and the need for the bottom nut of the gauge frame to be above same.

l didn’t manage to “drop a plug” in 10 years of firing 12” to the foot locos!

Thanks for your kind offer of a set of drawings but I have a set already.

Cheers

Dave

David:

" I have recently seen references to the MELG model engineers boiler test code AKA the blue book. "

A not KA the 'Blue Book' ! That is a previous edition and should no longer be used. The covers change colour with each edition, for easy identifying. The current one is white with orange lettering.

It is not restricted, and should be available from any of the several model-engineering federations represented by the MELG. Pandemics permitting, it is usually also for sale on the Federation stands at model-engineering shows, but of course...

Really, clubs ought also hold copies available on loan to their members.

.

You mention fusible plugs... Thinking now, it would seem, is that these are more trouble than they are worth on a miniature engine; and can create problems of their own.

Doh!!!!!!!!

That's interesting about the bottom nut of the gauge glass needing to be above the firebox top surface, On full sized industrial boilers, the rule usually is that the point where the gauge glass pipework/fittings attach to the boiler must be slightly above the top heated surface, be it tube or firebox crown depending on boiler type. Then the bottom gauge glass nut must be slightly above that level, so that when there is no water visible in the glass, you can still have an inch or two of water over any heated surface.

That way, if you look up and see no water in the glass, before adding cold feedwater and possible blowing a red-hot crown or tube, you shut the top gauge glass cock and look for water to rise up the glass. If water comes up, you have water at the bottom pipe connection and thus above any heated surface. In this case, it is safe to open the feed control bypass valve and add more feedwater. But if you shut the top cock and no water rises up, you shut the fire and feedwater off immediately and the next steps you take are boiler room steps two at a time, lunchbox and coat in hand.

But having the bottom of the glass below the firebox level sounds very dangerous to me. Is that done because of limited space at model sizes?

Edited By Hopper on 09/07/2022 06:34:11

You are probably right that the cramped nature of a model often places the bottom gauge-glass fitting lower than it should be, but the visible part of the glass must still start reasonably above the highest heating surface.

That on the loco the subject here, is totally wrong by both full-size and model-engineering practice, probably by the builder misunderstanding that point; and the only practical solution would be to replace the lower fitting with one that hides the lower portion of the glass.

It's also odd that he fitted a protector to the water-gauge on the tank, but not to that on the boiler.

On some boilers, both full-size and miniature, the gauge-frame is placed at an angle to allow a readable length of glass.

Ideally, the bottom nut of the water glass should be above the crown but it is acceptable if a permanent shroud is used to show the lowest water level.

The UK Boiler Test Code 2018 - Volume 1 – Boilers 3 bar litres to 1100 bar litres states:

6.7 Water level gauges shall be so constructed, mounted, or adapted such that the lowest water level visible in the gauge glass indicates that the level of water is above the firebox crown sheet.

The Australian AMBSC Code Part 2 for steel boilers states:

5.4.1 The bottom (visible) end of the glass shall be above the crown by not less than 10% of the distance from the crown to the outer wrapper

Apologies for diverting the thread, but my reading says it's a myth that boilers burst when water is sprayed on a red-hot crown.

During the steam-age thousands of boilers caused havoc by bursting. The reasons were studied carefully, resulting in dozens of safety measures: water treatments; duplicated pressure gauges, water feeds, and safety valves; tamper-proof safety valves to stop 'real-men' weighing them; automatic feed and shutdown; fuseable plugs; mandatory inspections and insurance; improved materials and design; plus ever harsher penalties for negligence and avoidable accidents.

At the time It was widely believed that spraying cold-water on to a red-hot surface would cause the resulting flash of steam to burst the boiler. Common sense, obvious innit. But experiments showed it's wrong. What actually happens is red-hot metal is so weak and plastic that it can't withstand normal pressure. The boiler shell sags and balloons while the stays stretch and tear out.

Best answer is to operate the boiler such that water never runs low! Next best is to kill the fire before anything gets red-hot. In the event the operator arrives to find a low-water emergency in progress, venting the boiler and spraying on lots of water is the operators best chance. Although adding water does indeed generate more steam, the main effect is cooling the metal, with luck restoring it's strength within the boiler's design safety factor before the shell gives way.

Whether to run away or not is an almost impossible decision. Staying to operate the controls risks the boiler blowing before it can be made safe. Running away risks injury if the boiler blows before you can get far enough away! As Boiler rooms aren't noted for ease of access, it might less dangerous to make safe than to run away. And the operator might be done for whatever he does.

My authorities are Victorian though. Maybe their experimental work was wrong or that a later development does cause modern red-hot boilers to explode when sprayed with cold-water?

Keeping a sense of perspective, its true that model locomotive boilers don't contain enough energy to be seriously dangerous. They're tiny compared with full-size boilers, usually operated carefully in the open, and are made of Copper which tends to give way gently by tearing rather than disintegrating violently. Not terrifying, but still energetic enough to cause expensive injuries and therefore must be operated responsibly. Blinding a child is traumatic for all concerned and the resulting financial liability for life changing injuries is enormous. Hence Clubs and Owners operating in public have to make sure boilers are properly certificated.

What's the biggest boiler in Model Engineering? I guess a big Traction Engine. I'm not in the least afraid of standing next to them, because they look well-built, their owners appear competent, and I know they require an up to date certificate. All reasonable precautions have been taken.

Dave

If you gave that answer on any of the industrial boiler operating engineer's license exams that I took on several continents, you would get a 100 per cent certain fail. You never introduce (relatively) cold feed water onto hot furnace or tubes in a boiler that shows no water in the glass when the steam cock on the glass is closed. Thermal shock can cause catastrophic failure.

The legally required procedure is to shut off the fire and feedwater, jag the safeties open to reduce boiler pressure to zero ASAP and call the boiler inspector to come and physically inspect the furnace crown or tubes for damage before the boiler can legally be fired again. He would probably want to do a hyrdrostatic test and then a proper steam pressure test too.

Boiler room steps two at a time with lunchbox and coat in hand comes after the foreman learns about all this.

PS, there is no need to take my outdated word for it. Here is the latest advice from industry: LOW WATER DANGER

Edited By Hopper on 09/07/2022 12:38:02

The accumulation test will only prove that the safety valves are adequate for normal hard working of the boiler ? If the crown sheet is already red hot then it is severly weakened and not even able to take the normal WP. Therefore introducing water into the boiler will generate more steam possibly by flash and well exceed the capacity of the safety valves and therefore there will be an increase in pressure.

For those who emjoy other peoples misfortune,AND the truly awsome power of steam, read " Historic Boiler Explosions" this should dispell any thoughts about cutting corners when making a boiler or using one ! Noel

Not so. Introducing cold feed-water would cool the boiler a bit, helping bring it back under control, especially if the feed is somewhere away from the inner firebox or flue.

The water will only flash into steam if it sprays straight onto the overheated plate, but if that is red-hot so already severely weakened, I suppose it might create local contraction strains enough to trigger collapse.

Static boilers were sometimes fitted with low-water alarm whistles, operated by a float.

According to one Edwardian engineering text-book I have, most boiler ruptures were traced to corrosion either internally or externally such as around poorly-designed brickwork settings, neglect or mis-use, and poor design of the shell itself. With the last, the most common factor was the structure being too stiff to accommodate the expansion and contraction, leading to grooving around the rivets and eventual failure.

Very happy to take Hopper's word for it! And his LOW WATER DANGER link says:

One of the most dangerous cases of low water occurs when water is added to the boiler, but the unit has already passed the “point of no return” where the boiler vessel is dangerously overheated. This causes the water to immediately turn into steam, leading to tremendous pressure being created, and the boiler potentially exploding. This is one of the most dangerous outcomes you can have with any boiler, and should be avoided at all costs.

C H Hewson's 'Locomotive Boiler Explosions' quotes part of a Railway Inspectorate report into an engine that exploded in Cardiff in 1909. With a worrying 200psi on the gauge, safety pressure 145psi, the engine had returned to depot because the injectors weren't working. The injectors didn't work because the pressure too high, actual value unknown because the gauge was pinned at 200psi.

After fixing a steam leak, the Ramsbottom Safety Valve had been incorrectly refitted with the washers on the wrong side of the slotted linkage, locking the valve closed.

It was suggested during the enquiry that the boiler burst due to cold water being injected, and the Inspector addressed the possibility:

I have another source which references the Boiler experiments referred to by Mr Carlton: if I can find it!

I lack the expertise to decide one way or another, but it's intriguing that none of the 1800 explosions investigated up until 1909 were caused by water entering a red-hot boiler.

Dave

It all depends on how fast you pump the water in and how well the safety valves cope. It takes a lot of heat to vaporise water, and if the water level is very low there is a fair bit of space to fill with steam. Thermal shock will be severe. 

Edited By duncan webster on 09/07/2022 20:30:07

Edited By duncan webster on 09/07/2022 20:30:34

A lot of boilers at that time were wrought iron, which may have reacted differently to more modern steel.

No. Every guide book to sitting the steam boiler operator's examination says specifically not to try adding water slowly in the case of no water in the glass. The thermal shock will indeed be severe and that is what causes cracks in plates and tubes, with possible catastrophic results. That's full size industrial practice of course. Models may be different. But I wouldn't like to experiment while sitting splay-legged astride the tender of a 7.5" loco!

Which raises an interesting question: There are steam boiler codes and legal requirements for the building and testing of model steam boilers and the issuing of certificates. But are the operators of such models required to have any training and/or pass any kind of test on their knowledge of safe boiler operation?

I didn't say it was a good idea, in fact I said it wasn't, as thermal shock would be severe. I'd think shutting down the fire and trying to release the steam pressure would be a better idea.

Edited By duncan webster on 09/07/2022 23:06:35