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Post by ettingtonliam on Apr 17, 2019 23:19:36 GMT
I need to make a couple of largish gunmetal flanged fittings which will be installed in the steam space of my copper boiler. Each has an end cap within the boiler which is secured by a number of 4BA csk screws. I was considering substituting 4mm csk stainless Allen screws, but when I told this to an acquaintence, he suggested that, in line with the prohibition on stainless steel for boilers in the UK, this might not be permitted.
I hadn't thought of it this way, but had thought of the stainless screws in the same manner as stainless components in boiler fittings, which are acceptable.
What do you think?
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Post by Cro on Apr 17, 2019 23:55:32 GMT
All my locos have stainless studs/bolts and where necessary I put stainless in my fittings. I think for fixings its ok and the rule of no stainless comes into play for physically manufacturing your boiler.
Adam
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Post by steamer5 on Apr 18, 2019 0:48:39 GMT
Hi,
Having to remove the remnants of the steel studs from my regulator Bush a few years ago.......8BA if memory serves......no mean feet, lots of pre planing I wouldn’t hesitate to use anything but stainless steel. If you are worried then find the correct grade of duplex & use that. BUT in either case check with your boiler inspector first!
Down this part of the world there is a boiler code for duplex boilers with a number in service, & quite a few more being built I understand. Not something that the average home boiler builder can build. One I’ve seen on a narrow gauge 7 1/4 loco is a large boiler & with an all up cost of somewhere in the region of $6500 NZ dollars materials & construction with a life expectancy of at least a copper boiler looks very appealing, the guys also reckon that it is faster to come up to pressure than copper.
I’ve had quite long discussion with our material guys at work, oil & gas industry, and they can see no great issues with a fired duplex boiler, providing a few simple things are done, ie use drinking quality water, regular blowdowns etc. should be fine. Time will tell. The only thing they figure that would be better is titanium!
Cheers Kerrin
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Post by ettingtonliam on Apr 18, 2019 5:31:04 GMT
Sorry to be ignorant, but what is Duplex?
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uuu
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Post by uuu on Apr 18, 2019 6:20:44 GMT
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Post by dhamblin on Apr 18, 2019 6:52:24 GMT
I'm currently making eight 10BA studs out of bronze to secure Britannia's top feeds in place, with another six 6BA ones to follow for securing the footplate structure onto the backhead.
Countersunk 4BA with a slot should be possible if you fancied the challenge of making them.
Regards,
Dan
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Post by steamer5 on Apr 18, 2019 7:12:51 GMT
Hi Wilf,
Thanks for posting that info.
Cheers Kerrin
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Post by ettingtonliam on Apr 18, 2019 8:09:19 GMT
I'm currently making eight 10BA studs out of bronze to secure Britannia's top feeds in place, with another six 6BA ones to follow for securing the footplate structure onto the backhead. Countersunk 4BA with a slot should be possible if you fancied the challenge of making them. Regards, Dan Not really, Locomotion presents enough challenges as it is! Unless anyone comes up with a strong objection to stainless steel screws in a fitting within a boiler, my preference is still the 4mm stainless csk allen screws, with stainless steel studding for the external fittings, such as footboard brackets (there are 14 of these!) and axlebox cradles, threaded into blind bronze bushes silver soldered into the shell. |
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Post by Roger on Apr 18, 2019 12:08:56 GMT
You could always make the few screws you need from Phosphor Bronze. I made a big batch of them for holding the boiler parts together.
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Post by atgordon on Apr 19, 2019 3:13:43 GMT
Most of my current contract CNC work is in stainless for use in ocean going sport fishing boats (impressive boats; 50ft long at 45 knots). I'm learning a lot about stainless from the folks I work with ... mostly, you have to be very careful where you use stainless steel when it is load bearing, or subject to stress (tension or torsion), and more importantly, the environment it is going to be used in (e.g. underwater with little free oxygen, or in wet and hot salt water situations). With careful selection of grade of SS, you can usually get the corrosion resistance you want, but it takes time and care to do so. Almost any grade of stainless used in wet and warm situations, where there is little or no oxygen (inside a boiler?) can be very problematic (oxygen is needed to form the chromium oxide coating that protects stainless). And where stainless is used in open air, but wet situations, particularly with salt or chlorine environments, problems can occur unless the grade has been selected for such usage. And then we get to electo-chemical effect when SS is in contact with other metals ... anything lower down the EC order (say Bronze) will become anodic (sacrificial) when in contact and in a conducting environment (like a steam loco?). Some stuff on SS corrosion here. I'd go with Dan and Roger and use PB. |
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Post by David on Apr 22, 2019 9:44:00 GMT
I read the drafts of our SS boiler codes and the way I read it was the main problem we have with its use is the perceived possible risk of cracking in the firebox with repeated heating and cooling cycles at firebox temperatures. I didn't read anything about corrosion worries, given non-stainless steel boilers are perfectly acceptable as long as the material used is thick enough to survive the corrosion for a reasonable lifetime for the boiler.
The duplex SS does not suffer from the risk of cracking at the temperatures our fireboxes can reach which is why we can use it.
Threaded fasteners do not go through these temperature cycles, being in much cooler areas of the boiler. "Everyone" (ie everyone I know) down here uses SS fasteners for things like domes, wet headers where the screws sometimes go right into the steam space, etc. Plus valve spindles, piston rods, and so on.
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Post by ettingtonliam on Apr 22, 2019 10:24:09 GMT
That was my original thought. The fasteners will be in saturated steam at around 160C (60 psi) and holding a flange in place. If the worst happens, then I simply remove the fitting and replace the screws.
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Post by Roger on Apr 22, 2019 15:09:23 GMT
I read the drafts of our SS boiler codes and the way I read it was the main problem we have with its use is the perceived possible risk of cracking in the firebox with repeated heating and cooling cycles at firebox temperatures. I didn't read anything about corrosion worries, given non-stainless steel boilers are perfectly acceptable as long as the material used is thick enough to survive the corrosion for a reasonable lifetime for the boiler. The duplex SS does not suffer from the risk of cracking at the temperatures our fireboxes can reach which is why we can use it. Threaded fasteners do not go through these temperature cycles, being in much cooler areas of the boiler. "Everyone" (ie everyone I know) down here uses SS fasteners for things like domes, wet headers where the screws sometimes go right into the steam space, etc. Plus valve spindles, piston rods, and so on. All true, but you can't quantify the rate of corrosion of stainless bolts in the boiler. Since the area of the bolts will be tiny compared to the huge area of the rest of the boiler, there's going to be a considerable current flowing. Presumably the bolts are there for a purpose during steaming, so having them fail is highly undesirable. It seems an unnecessary risk to take when you can make screws from a material which definitely won't have any issues. Why risk a failure for the sake of a little effort? |
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Post by chris vine on Apr 22, 2019 21:05:18 GMT
Phosphor Bronze, PB102 is very strong stuff. It might even be stronger than lots of grades of stainless. It certainly won't corrode.
Chris.
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jma1009
Elder Statesman
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Post by jma1009 on Apr 22, 2019 22:36:12 GMT
I make all my boiler bolts for fittings, inner dome bolts, regulator flanges etc out of non-magnetic austenitic stainless on boiler work.
I once removed a magnetic stainless regulator rod on a club loco that was rotten and badly corroded.
Alec Farmer was quite keen on blind tapped holes in boiler bush flanges for the dome and regulator and smokebox wet header which I have attempted to follow. Whether David Piddington followed Alec's advice I don't know in respect of 'Locomotion'.
Just to comment on Chris Vine's post, I've had PB102 phos bronze bolts shear off when removal has been required on boilers, but never my non-magnetic stainless (when replacing the superheater elements trying to remove the wet header bolts, and other bits). I always turn these up as sort of fitted bolts with a plain shank beneath the bolt head to suit the outer flange thickness. They are a real pain to make in tough stainless, but well worth the effort IMHO. I keep a separate set of dies for this job on stainless in HSS.
Cheers,
Julian
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Post by Roger on Apr 23, 2019 11:32:13 GMT
I make all my boiler bolts for fittings, inner dome bolts, regulator flanges etc out of non-magnetic austenitic stainless on boiler work. I once removed a magnetic stainless regulator rod on a club loco that was rotten and badly corroded. Alec Farmer was quite keen on blind tapped holes in boiler bush flanges for the dome and regulator and smokebox wet header which I have attempted to follow. Whether David Piddington followed Alec's advice I don't know in respect of 'Locomotion'. Just to comment on Chris Vine's post, I've had PB102 phos bronze bolts shear off when removal has been required on boilers, but never my non-magnetic stainless (when replacing the superheater elements trying to remove the wet header bolts, and other bits). I always turn these up as sort of fitted bolts with a plain shank beneath the bolt head to suit the outer flange thickness. They are a real pain to make in tough stainless, but well worth the effort IMHO. I keep a separate set of dies for this job on stainless in HSS. Cheers, Julian Hi Julian, I'm surprised you can get Silver Solder to wet any kind of Stainless Steel if you're going to rely on a seal being made. We used to Silver Solder Brass fittings to a Stainless Steel tank for a heat exchanger until we discovered that a sharp knock would shear the pipe right off the Stainless Steel. When you looked at the part, the Stainless Steel was as clean as a whistle and the whole Silver Solder fillet had just pulled away, there was no adhesion to the Stainless Steel at all. |
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jasonb
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Post by jasonb on Apr 23, 2019 14:28:05 GMT
Roger if you use tenacity No 5 or HT 5 flux it has something in it which will remove the chrome oxide that forms on the stainless and wet it nicely. Normal Easyflow won't remove the oxide.
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Post by Roger on Apr 23, 2019 14:40:24 GMT
Roger if you use tenacity No 5 or HT 5 flux it has something in it which will remove the chrome oxide that forms on the stainless and wet it nicely. Normal Easyflow won't remove the oxide. Hi Jason, That's interesting. What's odd is that the surface appeared to wet, there was a lovely fillet that tapered down to nothing. I think I'd be worried that it looked fine but the joint wasn't sound and in an inaccessible place. Personally, I'd use Phosphor Bronze and take the question mark away altogether. |
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jma1009
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Post by jma1009 on Apr 23, 2019 19:37:42 GMT
Hi Roger,
Apologies for my poor syntax - it is only the bolts that are stainless, not boiler bushes or regulator flanges or smokebox flanges/bushes.
Cheers,
Julian
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Post by ettingtonliam on Apr 23, 2019 23:25:15 GMT
Hi Roger, Apologies for my poor syntax - it is only the bolts that are stainless, not boiler bushes or regulator flanges or smokebox flanges/bushes. Cheers, Julian Thats how I read it in the first place Julian. I've been wracking my brains (whatever is left of them) trying to think why Roger suddenly started talking about silver soldering stainless steel! Yes, David has followed Alec's practice and used thick wall gunmetal bushes fo various things including the cylinder mountings on top of the barrel, with the stud holes all safely in the thickness of the bush wall. I've gone one further and used blind PB bushes where David specified blind tapped holes in the shell for various other fittings. The fixings that started off this discussion are for the cylinder bottom end covers, which, because the cylinders are mounted on top of the boiler and partially submerged in it, are in the steam space of the boiler. The load they take is minimal, really only to provide a seal. The boiler pressure is acting to push the cover on to the cylinder, and even when the regulator is open and steam in the cylinder, the net pressure will still be of the order of 10 psi or so pushing the cover on. David didn't specify a material for the screws, but as he did suggest sealing them over with Comsol on final assembly, I suppose he intended ordinary steel to be used. I settled the matter (or so I thought) this sfternoon, by buying some 3mm stainless csk Allen screws when I was at my local fixings suppliers, but then after I had got home, realised that to replace 4BA screws, I should have got 4mm----. Grr. Still, the 3mm must come in for something around the loco. |
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