steam4ian
Elder Statesman
One good turn deserves another
Posts: 2,069
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Post by steam4ian on Mar 14, 2009 0:11:54 GMT
G'day all
I need to get something off my chest. A new AMBSC Code for Stainless Steel boiler is being presented for ratification at the AALS Convention (Castledare WA).
I am concerned over a number of issues.
Firstly the haste in which the matter is being presented. I understand few people have had access to the code, SASMEE got one from "under the counter", apparently other clubs have not been so lucky. I am well familiar with engineering codes and know that changes and new codes come out as Drafts which are well publicised and available, comments are invited.
Secondly, the material is stainless steel for which I can list a string of catastrophic failures. Stainless steel is an alloy with galvanic couples just waiting to get their chance to corrode; even a difference in temperature will set up a couple so weld zones are particularly vulnerable.
Thirdly stainless steel relies on the chromium oxide coating for its corrosion resistance, chrome is one of the alloy elements. For the oxide coating to work it must be in an oxidising environment. traditionally boiler water conditions have been kept deliberately anoxic the very opposite to what is best for SS.
Fourthly, because of venerability to anoxic conditions it is subject to crevice corrosion as at screwed connections.
Fifthly, any metallic surface inclusions like marks from vice jaws and clamps can form galvanic couples, the end result is a hole.
Finally (Did I hear an Ahh! ?) is the attitude which I heard expressed by SASMEE member I would have though better of. "Stainless Steel Boilers will not need inspection, this material is so good."
This last attitude greatly worries me. I can only agree with one part of statement, it will be no good inspecting an SS boiler because if it is going to fail it will do so before the first inspection. This is consistent with what I have seen of SS in service, condenser pipework that didn't last to the first steaming, cooling water pipe that leaked before the project was handed over, a fire water tank that burst in the top of a major building when the internal braces gave way.
If these problems are addresseed and the RIGHT ATTITUDE is established we may be able to obtain boilers at much lower cost.
If I have one recommendation it is that the word "Stainless" be dropped and that the words "High Alloy" be used instead.
End of rant, I hope somebody takes notice before the model steam fraternity has its first fatality.
Regards,
Ian
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Post by alanstepney on Mar 14, 2009 7:29:15 GMT
That surprises me. The Australian code has long been known for its conservative approach.
Indeed, some of the well known and oft-used British designs wont pass "down under".
That they will introduce any new code without careful checking and consultations, seems, at best, unwise, and at worst risky.
My views on stainless steel for boilers are well known. I am against it.
(Yes, I know some countries in Europe allow it, but that doesnt mean it is the best material.)
I would hope that the AMBSC re-think their attitude and, at least, allow some discussion on the subject.
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Post by Tel on Mar 14, 2009 9:00:45 GMT
Now that is a bit of a surprise! Can't really comment as I've been out of the loop for a good few years now but it certainly would never have happened when I was boiler inspecting!
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Post by ettingtonliam on Mar 14, 2009 9:52:47 GMT
I don't know anything about stainless steel boilers in small sizes, but I did have some involvement many years ago with welded stainless steel vessels and pipework for the nuclear reprocessing industry. The problem with stainless is there are so many different grades, all with different charactaristics, you have to be exactly sure what you have got and that its appropriate for what you are doing with it. I regard stainless in fabrications subject to high temperature and pressure as treacherous stuff, and I wouldn't even think of having a boiler made out of it. We got a warning not to write or mark on pipework or vessels with felt tip pen, or use insulating tape as a marker, because at certain combinations of temperature and pressure, a chemical component of the ink, and the adhesive (and after all these years I can't remember what the chemical was) could cause corrosion and cracking in the metal. Do you think its a good idea to make boilers out of a material which is this sensitive? My advice is - stick with copper or welded carbon steel boilers.
Regards
Richard
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Myford Matt
Statesman
There are two ways to run a railway, the Great Western way, and the wrong way.
Posts: 621
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Post by Myford Matt on Mar 14, 2009 10:43:26 GMT
Given that copper is easily sourced, tried and tested over decades, if not a century, why is anyone bothering with SS?
I've nothing against progress, but where is the progression here?
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Post by havoc on Mar 14, 2009 11:12:19 GMT
SS boiler are used in Belgium for years now (more than 25 years in one of the clubs) without any of the problems you mention. And they are used more an more, the club in question even prefering them. And I do know that the new rules being written will include SS.
Again one of those "tradition" issues?
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Post by alanstepney on Mar 14, 2009 12:25:16 GMT
No, it isnt traditon.
There are two issues, safety and, less importantly, what are the advantages.
In fact, SS is LESS efficient as a material to transfer heat to the water, which is an important consideration.
Safety has been covered many times so I wont repeat that here.
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Post by baggo on Mar 14, 2009 12:28:45 GMT
Given that copper is easily sourced, tried and tested over decades, if not a century, why is anyone bothering with SS? I've nothing against progress, but where is the progression here? My sentiments exactly. What is the supposed advantage of using stainless over copper? Cost? Ease of building? I believe the Southern Fed has removed the 'Coded Welder' stipulation for building steel boilers and replaced it with 'Competent' meaning that basically anyone who considers themselves a welder can now build a steel boiler (God forbid  ). Would the rules on stainless be just as lapse? I can visualise stainless boilers being built out of old kitchen sinks etc.  John |
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Post by drjohn on Mar 14, 2009 12:45:28 GMT
AMBSC and boiler safety ---- don't make me laugh, I'll hurt my hernia!  DJ Unless, of course, it's a government enforced policy and they intend to export them to Muslim countries like here  |
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Post by havoc on Mar 14, 2009 12:54:00 GMT
The only disadvantage I see is the thermal conductivity of SS. As far as availablility goes, anything is easier than copper here. Once you want something else than the usual water pipe up to 54mm it becomes almost impossible to obtain in "small" quantity. Unless you call a 2m x 2m plate small and cheap.
As for safety, the record here says they are just as safe.
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Post by ilvaporista on Mar 15, 2009 7:53:15 GMT
In Italy I am laughed at when I raise the issue of stainless steel boiler safety. 95% of all new ME boilers here are in stainless.
Copper is very difficult to get hold of here in small quantities and in 'our' range of szies. All my boiler materials have been imported form the UK.
As for cost I had had a SS boiler made for me by a reliable boiler maker at 350 Euros compared with 1600 pounds requested for a copper one from the UK.
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jackrae
Elder Statesman
Posts: 1,335
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Post by jackrae on Mar 15, 2009 8:34:28 GMT
OK folks, accept as fact that ss boilers do exist and are within the acceptance criterea of the respective agencies so let us look at the topic in a constructive sense
What I'd like to know is :
1) what grades of ss are permitted by the design codes where its use is permitted
2) are there stipulations as to how joints are made (welding, silver solder or whatever for barrel joints, tubeplate to barrel, tubes to tube plate etc)
3) what is the pressure testing regime requirement for ss - does it vary from those of copper
4) are there an limitations placed on the quality of water used for steaming
5) is there regulation as to what chemicals are used to minimise corrosion
regards
Jack
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Post by alanstepney on Mar 15, 2009 9:29:38 GMT
Jack, right now, in the UK, we cant use stainless steel for boilers.
What people may do in other countries regarding the questions you raise, I have no idea.
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jackrae
Elder Statesman
Posts: 1,335
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Post by jackrae on Mar 15, 2009 9:56:58 GMT
I appreciate that Alan but it doesn't mean we can't ask questions
jack
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steam4ian
Elder Statesman
One good turn deserves another
Posts: 2,069
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Post by steam4ian on Mar 15, 2009 10:26:22 GMT
G'day Jack
My intention is not to permanently can "High Alloy" Steel Boilers (call it stainless steel if you must) but rather to trim the speed of progress so that there is sound control of the end result. There are icebergs so why go full steam ahead, even stainless steel will corrode, it is not unsinkable.
I make my comment about the name very strongly. The name "stainless steel" engenders a foolish ignorance of the hazards which do exist. Imagine if when going from wrought iron boilers to Bessemer steel boilers the latter had been considered foolproof obviating the need for inspection. It would not have happened.
I agree with Jack's list of conditions; tick each of these boxes and we have a goer.
If I can get a complete, certificated High Chromium Alloy Steel boiler for say AUD 1500* I will be very happy. (*Copper raw material kits for a Simplex, Blowfly or Sweat Pea boiler are currently listed at under AUD1000. I estimate that the purchase of solder, flux, a gas welding kit and gas/oxy bottle hire will set me back another AUD1000.)
BTW I have had more than the usual professional experience in Cathodic and Galvanic Protection which leads me to be cautious.
Regards,
Ian
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Post by havoc on Mar 15, 2009 10:51:14 GMT
I can only answer a few of those as I don't have the complete spec. Also bear in mind that in a few months there will be a "new" spec (for all types of boilers):
1: 316L
2: completely welded
3: same as any other boiler: 2x working pressure first time, 1.5x afterwards
4/5: no idea
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Post by Laurie_B on Mar 15, 2009 11:45:31 GMT
That simply wouldn't be suffient information.There are many types of welded joints and there are various design codes for boilers and pressure vessels that require the exact weld design to be specified. Most copper boilers rely on full penetration silver soldered joints for their strength.I can't see a tiny external fillet weld holding in a firebox backplate that well,and there wouldn't be access to weld on the inside. I suspect the whole design for a stainless steel boiler would need properly appraisal. |
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Post by havoc on Mar 15, 2009 12:22:16 GMT
As I said, I don't have the part for SS at hand and it is been updated. But regarding the question Jackrea asked: all parts have to be welded, no silver solder. And like any other boiler, the design has to be approved, drawings provided, welds preparing and type indicated etc. Just like any other boiler be it copper or steel (or chocolate).
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Doug
Active Member
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Post by Doug on Mar 15, 2009 14:58:28 GMT
Again one of those "tradition" issues? The avoidance of stainless for boilers is hardly a tradition issue. There is good engineering rational not to use it. Anyone touting stainless as a good material needs to do a search on "stress corrosion cracking" on the web. Here is something from the first site that came up for me: "Austenitic stainless steels may be susceptible to chloride stress corrosion cracking (CSCC). The standard 304/304L and 316/316L grades are most susceptible. Increasing nickel content above 18 to 20% or the use of duplex, or ferritic stainless steels improves resistance to CSCC. High residual or applied stresses, temperatures above 65-71C (150-160F) and chlorides increase the likelihood of CSCC. Crevices and wet/dry locations such as liquid vapor interfaces and wet insulation are particularly likely to initiate CSCC in susceptible alloys. Initiation may occur in several weeks, in 1-2 years or after 7-10 years in service." I was first alerted to the problem by a nuclear engineer. The nuke industry does use it as they have found no better material for their application, but SCC is a constant problem for them. I was given data years ago concerning stainless failing due to SCC in applications not involving pressure vessels, and at lower temps than listed in the quote. Two that stick out in my mind were non pressurized tanks that received sea mist, and implant joints in the human body. Regards, Doug |
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Post by mutley on Mar 15, 2009 16:55:22 GMT
Jack, right now, in the UK, we cant use stainless steel for boilers. What people may do in other countries regarding the questions you raise, I have no idea. Thats not my understanding Alan. The red, soon to be blue, book says that ME Societys can not test a SS boiler. You can use a SS boiler IF you can find a comercial tester willing to test it for you. Last I asked the question no one that I spoke to was willing to test one. Andy |
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