Stainless steel boilers

[stantheman]

Just to clear the wood from the trees, the wording from the Blue Book on Stainless Steel Boilers is to be found under Appendix A page 17. (By the way copies of this Blue Book are available now and can be obtained via the Southern Federation M.E.S web site.)
So it reads...'The examination and testing of stainless steel boilers is not permitted under this code. Due to the specific requirements and difficulties associated with the examination and testing of stainless steel boilers it is suggested that owners/users of such boilers should seek the services of professional/commercial organisations.'
Stan

[grahamo]

I've been watching this thread with some vested interest as I have installed st/st in idustrial steam and condensate lines (though not on Boilers), I've read some of the wikipedia links with interest and learnt a few things from it.

Our st/st steam lines tend to be on <4 bar supply lines and have been specified by clients as they last longer than the equivalent carbon steel lines. Our lines feed food processing heat exchangers also in st/st and I kow of units that have been in service 20 years without failure.

Acording to the articles I've read, the stress cracking is said to become an issue over 50C and under pressure, well almost every food processing line that I know of is washed with caustic or dilute acid solutions at 50 - 90 C under pressure and many are steam or hot water sterilised, and they remain as new (we cut through many of them to modify systems and there are often no signs of any corrosion).

Chlorides do wreck "normal" st/st however, bleaches are bad and I've dealt with a process vessel that contained a "neutralised" hydrochloric acid that coroded through within 10 months.

The scary thing with the vessel was that it appeared sound until it cracked, it was then realised that the area (in the heat affected zone of the weld) was foil thin, not 2mm thick as manufactured. There was no visible effect of corrosion. The vessel was 316L grade st/st.

We used a duplex st/st as our research showed it to be the most resistant to the HC acid. 304 & 316 st/st can be tough to work but the duplex stuff is a real b*tch. Brittle unless annealed, hard as (very hard) nails it ruined cutting blades and requires specialist welding techniques as over heating wrecks its resistance properties.

When there have been corrosion issues with st/st boilers I suspect welding quality, or chemical action especially chlorides would be involved (could chlorides be produced by the fire?). My st/st experience on steam lines would lead me to think it would otherwise be suitable, but the worry would stem from my experience with the acid tank in that without drilling holes or x ray equipment, you'd not know if it had coroded, and visual inspections would therfore be of little use.

Graham

[weldsol]

Hi Graham what you describe is weld decay where the carbon has snatched the chrome at the HAZ taking it below 11.5%. the normal cause for that is welding with a non stabilized filler. the filler should normally be niobium stabilized to stop this.
Yes Duplex & super Duplex is a bugger to work with and although the best for resistance to chloride attack It is not the easiest to weld ( I will rephrase that to not the easiest to weld and achieve the required properties)

Paul

[steam4ian]

G'day all

A colleague on a project knowing of my opinions handed me a Hilti fasteners booklet about corrosion resistance. What I read about SS supported my contentions.

One point of interest was that SS which included about 6% Molybdenum was more resistant to Chloride attack than even 316L. I don't know what this additive does to machinability and weld-ability.

Regards
Ian

[havoc]

Next question: is this chloride attack a problem in our application?

I mean that a vessel that needs to contain "a "neutralised" hydrochloric acid" is hardly comparable to a steam boiler that is used once a month for a couple of hours. Same for pipes being sterilised with bleach at 90°C. Or a nuclear application at 300bar and irradiation. Most of us aren't running with seawater either.

You can find a problematic application for each material you name. In our case the application is a fixed parameter.

[steam4ian]

G'day Havoc

I agree that we need to beware of quoting exotic situations but also need to make sure we are not creating one. On another site I read some bloke's treatise on water softening. He advocates using ion exchange softeners. BUT he is replacing a carbonate problem with a chloride problem. I would rather the carbonate problem, at least that can be periodically boiled out with Citric or Acetic acid (lemon juice or vinegar)
Chlorides kill steel boilers including SS.

I have said earlier I am not against 'High Alloy steels in boilers. I am against ignorance as to the potential problems and the ways of mitigating against them.

For those who use so called SS boilers let us know the service experience and what regimes are used to control any corrosive possibilities. It may be that tap water is used, if so how "hard" is it? and has it been chlorinated? Are the boilers blown down to empty at the end of a steaming? Are special alloys used or is it say 316? What post heat treatment is used? What welding techniques? Who is considered competent to weld the vessel? Who is considered competent to inspect it? How often is the boiler inspected? Is it simply pressure tested or is a boroscope used or ultrasonic gauge?

Regards,
Ian

[glent]

Just a little bit of clarification. In 2008 there was a sub committee apointed to investigate the use of UNS S31803 Duplex Steel for boilers covered by the existing boiler code. This committee is to make recomendations to the 2009 AGM in Perth Western Australia.These recomendations will then be considered for discusion for comment not for ratification as has been spruked by an earlier writer. Yes the draft states that it is an Stainless Steel Alloy 2205 which has been nitrogen strengthened. Maybe people should get all the facts before creating humbug on a forum. Instead why not offer knowledge to the AMBSC to move forward in a positive manner.
Enough of my ranting.
Glen

[Deleted]

We were warned off stainless boilers years ago on the grounds that sulphur from the coal would have a deleterious effect on the welded joints in the region of the firebox. Never had enough practical evidence to prove/disprove the theory, but no-one was prepared to take the chance while copper and silver solder were so readily available. Anyone with any real experience of this?

[havoc]

Why not brush up your french and take contact with PTVF in Brussels? On their site they list having 25+ years experience with SS boilers and prefer them for any new boiler. I have seen them there as series of 8 pieces at an open day (about Sweat Pea size). Site is ptvf.fte2.org/ Click "Le PTVF", then "Notre Association", then "Réglements" and finally "Chaudières". Go read it, contacts persons for questions about it are also mentioned and addresses given.

OTOH if you want to re-invent the wheel because "not invented here" go ahead.

[Myford Matt]

Three points:

First, I think we forget just how dangerous our boilers are. Relative amateurs are building/using quite large boilers, filled with very hot steam under considerable pressure – often near members of the public. Most of these pressure vessels (bombs on wheels) are not made in certified factories by experienced engineers under controlled conditions, but by enthusiasts with very limited experience or knowledge. It should be a disaster, but thanks to the accumulation of accepted construction practices, tried and tested designs and knowledgeable boiler testers there appear to be extraordinarily few problems. This has nothing to do with the technology, and everything to do with the safety regime that the model engineering fraternity has built up. For better or worse the knowledge base of that regime is founded on copper/silver soldering. It could just as well be stainless steel, mild steel or anything else, but it isn’t. We ignore the great value of that intellectual capital at our peril.

Second, I am still none the wiser as to what the advantages of stainless steel are. I do understand that there are places where copper is hard to source, but that doesn’t make the alternatives good (or bad) choices. If our continental friends are using them successfully then good luck to them, but are they better, worse, or the same?

From a personal perspective I like the idea of making a boiler in the tradition of Greenly, LBSC and the like. Model engineering is about traditions – why else make a steam locomotive in the first place? Much of what we do is anachronistic and has little to do with modern engineering practice. I have no problem with that – none at all. This is a hobby, it’s about the pleasure of design and making, not pushing the technology envelope. I’m no luddite, I enjoy using CAD, but a boiler is the heart of a locomotive and to me stainless just ‘feels wrong’.

[ripslider]

Apologies if this is a stupid question, but what materials ARE considered safe to use and what forms that decision?

Copper is obviously on the list, but has it's own SCC issues, this time with Ammonia + heat. Stainless would seem to be off.

So could I use other materials? I know a chap who can weld up a storm with boron steel and has certificates and very fancy welding machines to prove it. It might rust, but it'll be tough as boots, and I can always get him to knock me up a new one becuase he owes me a favour.

How about Aluminium? The same bloke who does the boron steel can weld Ali so well it looks like a robot has done it. 7000 series is very tough. 4000 series very corrosion resistant. Certainly a lot of car engines using it now, even diesels, which high pressures and high temps.

An ex-member of this forum assumes me that Titanium can be worked well, and so I have placed an order for some ( for my fish tank--- don't ask ). Could I use this on a bigger scale?

Right at the crazy end of the spectrum, the newer high M carbon-fibre/kevlar mixes and the 4G resins will handle both the heat and the pressure. Equally, Basalt-fibre will do the same for much reduced cost and can use cheaper resins, but looks very ugly and will lead to a fluffy boiler.


I don't mean this to be read in an aggressive manner, but as a new entrant to the hobby I'm finding the whole boilers issue confusing. It would cost me a lot, and be well beyond my current skill set, to construct a copper boiler. BUT, it would take a week of evenings plus a sataday pass from Mrs Steve for me to have the same, complete, carbon-fibre/kevlar boiler built and cured which would exceed any pressure test that a copper boiler could, and I already have everything I need in stock apart from some metal tubes for the inside. CF is MUCH quicker to work with to make hollow shapes like boilers.

But I'm assuming that even if I built it, and it exceeded all safety testing, it still wouldn't be "legit". But I'm not sure why?

Steve

[NickM]

Ripslider,

I think that cost effectiveness is the appeal of stainless boilers. Much cheaper than copper, the money no object choice and only a bit more expensive than steel but much longer lasting.

I can't comment on boron steel or aluminium and whilst I would think titanium would do a sterling job, at what cost?

Some carbon fibres are certainly up to the pressure requirements and have excellent fire resistance but I don't think that is the same as being exposed to a coal fire for hours on end as in a firebox. Whilst the carbon fibre will protect a steel structure in the event of a fire, I doubt if it would offer that protection more than once!

[grahamo]

My comments regarding Hydrochloric acid were intended to highlight that st/st is not perfect but that it can take a fair amount of punishment. Having worked with st/st since the early 80's it's the only real corrosion problem I've encountered that 316L would not survive.

The 2205 duplex referred to by Glent is the stuff we eventually used but (in the UK) this is not easily obtained worked or welded......

St/St has potential advantages, "normal" grades are common and available easily, can be nicely tig welded with little distortion but the main advantage might be lifespan if they prove to last longer than carbon steel.

We've heard of failures, but does anyone know the cause? were chemicals involved? do the fires cause issues with sulphur or chlorides? Was construction / inspection at fault?

If the doubts could be answered and the boilers built safely, it may not be to everyones taste but would provide another option for those who want to go that way, it will be interesting to see and understand the Australians conclusions, but in the UK we must remain conservative and ensure club inspected boilers do not fail otherwise all our amateur built boilers will become a thing of the past.

[havoc]

We better drop this. It is leading nowhere.
1: It is clear that no-one is interested in going to talk to people that have experience because it isn't in the UK and it isn't traditional.
2: There is a lot of anecdotical references to "failures" that have nothing in common with our application but not a single reference to a failure in model boilers.
3: there is no engineering spirit around wanting to lift this hobby out of the 18th century.

[alanstepney]

To cover some of the points raised,
Andy, Stan, as you say, clubs cant test SS boilers, and that would cause problems for 90=% of model engineers, and, should you try, you will find that almost all the commercial insurers in the UK, wont touch them either.
Hence my comment.

Matt, I do agree with your comments, especially the first one.

Steve, copper is still THE best material for the smaller boiler, and that includes the vast majority that "we" build.
It has been proven that by following fairly basic instructions, a person with little or no prior experience can build a boiler that is safe and long lasting.

The reason that many of the alternatives wouldnt be "legit, as you put it is because you couldnt get it insured.
Perhaps not a problem if it is only to be used on your own property, but that would certainly exclude you from operating in public.

[Tel]

Well put AJ.

Havoc, the point is not whether we want to lift ourselves out of the 18th century or not - it is that most countries do not allow for them to be used in our application - no inspection, no insurance, no go! As Glen rather bluntly put it, the AMBSC is taking the matter under consideration here, so the situation may change as far as Aus is concerned, but even if they become 'legal' it would be a slow process getting people to come on board with the new system. Does anyone know if any other countries, other than Belgium, allow 'em?

[havoc]

Tel, if no-one is prepared to do the study for our application it will never happen. Using an undocumented failure of an unknown alloy in an unknown application as an excuse for trowing your hands in the air and claiming it can't be done doesn't give much hope that any sensible discussion will follow. So bringing the issue up for consideration is fine but from the replies here I don't think it will go further than rethorics.

[Tel]

Yes mate, I understand what you are saying, but you have to expect resistance from the older members especially. For instance I have been modeling for about 35 years and have built quite a few boilers during that time in copper and steel, now, in my 60's am I going to get excited about learning a whole new set of procedures? - probably not. It will fall to the younger modelers to develop and prove the system.

[davebreeze]

Just from what I have seen in magazines and on the web I have the impression that SS boilers are common in mainland Europe in general. I've certainly seen articles/pictures of them in use in France, Germany, Belgium and Italy.

I read a long article on building and using ss boilers on a French website, I'll see if I can find it again.

I do think in this hobby in the UK we should pay more attention to what is going on in the rest of the world, especially the non-English speaking parts. While I understand the theoretical problems with using stainless steel, there is obviously a large amount of experience and knowledge on the subject out there that we are not tapping in to.

[steam4ian]

G'day Havoc, Glen

Please don't take this discussion so personally.
Unfortunately my French would need a bit more than brushing up, the curse of being monolingual..

I for one would welcome your translation of the "foreign" standards and procedures applying to stainless boilers used on models in places other than the UK.

Unfortunately not everything translates. A somewhat obtuse example is the lead pipes used by the Romans. Because of experience with lead contamination of drinking water in one country it has been postulated that the Romans all suffered from lead poisoning. This fails to take account of the differences in potable water between differing places. Due to the limestone in Italy much of the water would be hard whereas in other places the water will be soft. The hard water will be buffered by the calcium dissolved in it and not leach out the lead, in fact lead carbonate would coat the pipes. You can see this in sections of pipes at Pompeii. On the other hand softer water would leach out the lead and there would be minimal carbonate coating. The same considerations of water quality would also apply to stainless steel.

Regarding the "anecdotal", I was a member of the engineering teams involved in some aspect of the incidents I have recounted.

Glen thanks for your comments; we we led to believe at SASMEE that ratification of the code was immanent.

Regards,
Ian