Boiler materials/fabrication

[Carl Wilson 4Participant @carlwilson4]

[Carl Wilson 4Participant @carlwilson4]

Hello all,

I have been rooting around some of the threads relating to boilers on this site. This has led to a number of questions. I don't want to hijack someone else's thread so I thought I'd start a fresh one.

First off, stainless steel. There seems to be an almost pathological fear of this, and I can understand to a certain extent as it seems that austenitic is prone to stress corrosion cracking in the presence of water and heat. Fair enough.

Ok, so what about duplex stainless? Apparently a boiler has been made in this in Australia. It seems to me also that ferritic stainless might be a contender.

Regarding fabrication, I have read somewhere that if a boiler is produced by welding, i.e. TIG, the welder does not have to be coded, but can submit test pieces to prove competency. So the welder has to be competent, but not neccesarily coded. Is this correct?

In terms of TIG welding a copper boiler, I'm thinking that OFHC copper could be used with a moderate preheat, (depending on thickness) then a filler containing silicon (SIF do one think it is called sifcopper). Also helium might be useful instead of argon. Alternatively instead of the preheat one could tack at much higher current to get some heat into the joint, then proceed as normal. I've done that with aluminium before.

Just throwing some musings out there. Interested to hear the thoughts they provoke.

[pauljamesParticipant @pauljanes79128]

Model boilers in Australia are built to a code published by the Australian Miniature Boiler Safety Committee and is for steel or copper boilers less than 50 litre capacity and less than 100 psi. This code is more strict in some ways than the code for building full size boilers and written to ensure that miniature boilers are designed, constructed and operated to a high standard.

It enables amateurs to build boilers but every stage of its construction must be checked and signed-off by a certified engineer who is familiar with boilers. Amateur welding should be under the supervision of a qualified welder.

It states that carbon steel or carbon-manganese steel should be used for its construction.

Steel plate to AS 1548, Seamless steel tube to ASTM A 106, A 53, Heat certificates are required for all materials.

Copies of the code for either a steel or copper boiler are available from the Australian Miniature Boiler Safety Committee.

Edited By Paul Janes on 01/12/2013 10:02:55

[Sub MandrelParticipant @submandrel]

Australian model engineers prepare to test a 'Tich' boiler:

Only jesting, antipodean friends

Neil

[Carl Wilson 4Participant @carlwilson4]

Afternoon gents and thank you for the comments.

Paul:- Thanks for going to the trouble to outline the Australian regulations. I'm intrigued as to why amateur welding has to be overseen by a professional. I would imagine that as part of the certification process the joints would have to undergo some form of NDT. If a joint is bad it will be so regardless of whether or not a professional welder watched someone do it. In the petrochemical industries, professional welders cut out and re-weld joints they have made all the time.

Stub:- "LOL", as I believe the young people say. As I recall this photo is of British and US Engineers dismantling a German experimental Nuclear Reactor at the end of World War 2.

Speaking of nuclear reactors, I believe they use duplex stainless in their "boilers". It seems that the 300 series (austenitic) stainless steels have too great an index of expansion. The cyclic heating and cooling is what leads to stress cracking in welded joints. It still looks to me like ferritic grades of stainless (400 series) could be useful for boiler construction.

With regard to duplex steels, look at this link:- **LINK**

This seems to me to be an innovative attempt to move things forward. That is what I am interested in hearing and learning about here. Not what should be done, but what could be done, taking into considerations the material properties and the end application. All thoughts welcome.

[Sub MandrelParticipant @submandrel]

On a serious note, I have still to read and ME/MEW article that explains the various routes to boiler making and certification simply and in a narrative way rather than just repeating parts of a code.

Neil

[JasonBModerator @jasonb]

Have a search for Fizzy's thread "a boiler for £200" he welded his own steel one and had the joints tested, think the testing cost about £60.

This is the thread

 

J

Edited By JasonB on 01/12/2013 16:15:38

[Carl Wilson 4Participant @carlwilson4]

Hi Neil,

Indeed. A good point and well made. It seems to me that the second one utters the word "boiler" it is a cue for someone to quote chapter and verse from one code or another.

What I'd like to see is a meaningful and measured discussion about the subject based around what materials are available and their properties. The link I included is to a report on the duplex stainless boiler built in Australia. Fabrication techniques have moved on so far what with pulse TIG and so on. When it comes to something like this appearing in ME or MEW I'm not holding my breath. There are a lot of knowledgeable and experienced people here it seems to me. So I'm looking forward to opening this one out a bit. It may well be that the old maxims prove to be the best. I'm interested in finding out.

[Chris PickardParticipant @chrispickard93756]

HI all,

Having been reading this and several other threads with ref to boiler manufacture using steel, stainless/duplex and copper….would just like to add my thoughts….

Seamless carbon steels of A106/60 a/b provide some of the best pressure pipe available to us as model engineers……under industrial conditions these could be working at massive pressures…with little troubles…

Again stainless is used in a variety of steam applications and although the expansion has to be calculated and allowed for it works very well..and has replaced the use of carbon steel in steel mains in many industries….the gas and oil industry uses a variety of duplex and super duplex steels in the most harsh environments …all are well proven for there applications…butt welds are generally always x rayed or at least 10% and visually inspected by a trained and certified welding inspector…Not a boiler inspector…two posts which are clearly different, but come together within the construction of pressure equipment.

whilst a competent welder would or should have little problem welding a carbon steel boiler or may b stainless steel…i would doubt that the average man in the street would be up to dealing with duplex steels,

Even as a professional tig welder working within this industry…duplex sorts out the men from the boys…not a difficult material too handle but you need to know how to handle it..both in heat input( ferrite count rises through excessive heat input, which in turn affects the corrosion qualities of the duplex family of steels)…also different backing and shield gases can be used with the addition of Nitrogen to aid the loss of nitrogen from the weld pool whilst welding…this helps with the stress cracking ….

one thing to remember is a good weld in any material is a good weld…if its passes a ndt inspection then its good……end of ….

just a few thoughts to throw in the pile…

chris

[Carl Wilson 4Participant @carlwilson4]

Hi Jason,

Thank you for the link. Fizzy's boiler is an excellent piece of work and gives the lie to the naysayers.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Carl ,

All this research has already been done very extensively both in model world and more rigourously in full size .

I you start seeking out information on full size boiler materials and construction methods you will rapidly build up all the information you need .

Be aware that the design of boilers is much more complex than design of simple pressure vessels .

In model size though here is a link to the Australian boiler that you mention :

Duplex boiler articles

Regards ,

MikeW
 

Edited By JasonB on 02/12/2013 13:15:11

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

See also this and follw some of the links as well :

New type of boiler

 

Edited By JasonB on 02/12/2013 13:14:26

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Apart from consideration of actual materials the detail SHAPE of boiler components is more important in steel boilers than it is in copper ones .

Many of the stress corrosion problems reported arise from sharp corners where there is an almost infinite stress concentration and a crack initiator built in .

For sound design and long life of a boiler flowing lines and radiused flanged joints are really needed .

Also all parts of boiler need to be able to expand and contract under varying temperatures without inducing what can potentially be high local stresses .

It all comes down to finesse in the end though – an agricultural boiler made of thick plate can be made to last the same length of time as a sophisticated design boiler made of much thiner plate .

MikeW

Edited By MICHAEL WILLIAMS on 02/12/2013 11:23:35

[Carl Wilson 4Participant @carlwilson4]

Hello Chaps,

Michael:- Thank you for taking the time to post and for the information you gave. I have read the articles on the duplex stainless boiler, the link you gave was the one I included earlier. As you suggest I have been reading around this topic generally. My background is in the Aircraft industry and I am more than familiar with the need for avoiding sharp corners and other potential stress raising features.

Chris:- Very interesting reading your comments. Although in my previous life I was an Aircraft man, for the past ten years I have been involved in subsea intervention engineering and I am familiar with the use of duplex steels in this industry. I remember a particular job last year…we recovered a subsea control umbilical, which for the benefit of other readers is a subsea pipeline that is made up of many hydraulic and electrical lines used to control subsea wells. We brought the umbilical up from about 1800 metres of the coast of West Africa. A specialist team of guys had come from Duco to TIG weld the duplex stainless hydraulic tubing on the gooseneck (end fitting with multiple quick connects). They set up a habitat on the back deck of the vessel and had, as you say, difficulty in welding the tubes. I think this stemmed from the problem of getting backing gas inside the tube, and the fact that it was very hard to ensure the tube interior was free of the working fluid. I managed to get several films watched whilst they did it though, so it wasn't all bad. Was that you by any chance?

I'm interested in what you say about the increase in the ferrites with excessive heat input, and the use of nitrogen to help with the stress corrosion cracking. I take it you use some sort of nitrogen/argon combo?

I find it odd sometimes that people can be very reluctant to discuss a subject, and will instead by way of a reply "throw the book at you"…in this instance the boiler codes. So thanks to all who replied.

Carl.

[Chris PickardParticipant @chrispickard93756]

HI All,

I quite agree with the comments above….with modern materials and design techniques…shell thicknesses and material weights have been slimmed to make up for more agricultural designs…having started life as a blacksmith….heavy and weighty was the way fwd….but as time progresses the fineness of more technical designs/materials have shown the way fwd….

Carl: …Dont think i was on that project to be fair….but ive done a fair bit on the north sea oil field and work for solome Voe, Shetland, the problem with repairs and working on pipes or vessels in situation, can always be getting a good and consistent purge…the backing gas is by far the important component of welding stainless or duplex steels…for good clean welds or xray standard welds theres no other way…coking of the root weld is not acceptable and basically ruins the properties of the stainless family….usually on thicker pipes after the 3rd or 4 th run the backing gas can be removed as the heat wont harm the root anymore…but to be safe generally its left on to protect just incase….

I've just been working on duplex/super duplex, heavy wall pipes from thicknesses of say 6mm-55mm plus, generally the heavy wt pipes are welded with a pure nitrogen backing gas….the shield gas can be either pure Argon or Argon/nitrogen mix approx 2% nitrogen…aids weld pool fluidness and helps with replacing nitrogen lost in the welding process…there's some very good articles on the twi site explaining how it all works….

The heat input to duple steels is another important aspect….the interpass temp( max welding temp) is around 100-150c…which as you can imagine is not very warm once you start welding…can take a long while to weld a butt or plate adhering to the welding procedure……generally once the temp is reached on a welding pass you would need to stop….allow to cool…either by forced air(blower) or natural cooling…

I have been involved in the welding of test pieces for new welding procedures and it can take many hours of careful stop start welding to achieve the desired results…these are the test pieces which are tested to prove how a material is welded and then test welders against this for there qualifications…can be very tedious…

I agree….that people seem quite frightened by using modern materials or discussing their applications even though they are proven in use in very extreme conditions…..

chris

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