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Duplex Steel Boilers

Rob Walker

Joined: 25-10-10

Topics: 6

Replies: 12

Posted: Wed 24th Sep 2014, 5:38am
Duplex Steel Boilers

Has any further advancements been made in the use of duplex steel for locomotive boilers, as I am currently looking to order a Thomas 2 boiler in copper but thought I would look into this as another option.

Replies To This Post


Joined: 1-01-85

Topics: 1

Replies: 2

Posted: Sun 19th Oct 2014, 5:38pm

I have read many of the articles about Duplex Boilers and I have sent for the Australian Boiler Code. I am currently building a Milner c19 2-8-0 and a Lawley 4-4-0. I would love to consider putting a Duplex boiler on one or both of these models. Having read the code there does not seem to be any real issues with cutting out the plate and welds preps etc. The issue comes when you need somebody to approve the design, test it, insure it and weld it. I am not a person who intends to run these models very often, so more deterioration is going to take place in my garage than out on the track in steam. From what I can see Duplex solves many of the issues of the boiler being laid up.

As an individual I feel powerless to move the design process forward with Duplex Boilers.
I think that there are people within the society who are involved in the manufacture of models boilers who might like to take the lead. Is the Lawley Boiler the same or very similar to the Thomas2 boiler? it was designed by Roger Marsh. If we could batch build a number of similar boilers maybe the initial one off costs for insuring the new methods of construction could then be shared.

I would be interested to know what others feel about this.

I would be interested in producing a design following the Australian Code as an proposal, which the powers that be could start discussing as a real project rather, rather than this strange new fangled method which seems to be being kicked into the long grass.

I would have thought that Duplex Boilers should be given a try, if there are insurmountable problems, then we can revert to our current steel and copper, but having heard of steel boilers failing after only a few years, then I think the Seven and a Quarter Society should support some trial builds, and see where this takes us.


Joined: 1-01-87

Topics: 3

Replies: 44

Posted: Sun 19th Oct 2014, 9:26pm

I'm not quite sure what you are saying here Ian.

If the code of practice relating to the Australian Boiler Code is not acceptable to the EU Pressure Vessel Regulators or to model engineering pressure vessel insurers in the UK then what is the point of the Society supporting trial boiler builds as these will be un-insurable and so illegal to use on tracks to which the public have access.

As I see it there must be a change in the regulations first and this is where the Society needs to be active in getting Duplex boilers accepted by the regulators and insurers.



Joined: 1-01-85

Topics: 1

Replies: 2

Posted: Mon 27th Oct 2014, 1:30pm

The whole point of my comment was, the Australians seem to have arrived a satisfactory outcome for Duplex Boilers, why cant Europe or the UK.

I am not a professional engineer so I not fully up to speed with legislation on pressure vessels, but surely somebody within the society probably is or knows someone who is.

Can somebody out there suggest how we can move forward on this?


Joined: 1-01-97

Topics: 9

Replies: 13

Posted: Mon 27th Oct 2014, 8:58pm

Although I have no doubt the knowledge to make duplex steel boilers exists in Europe, does the will to make them, and how much cheaper than a copper boiler would they really be. Also will the authorities be willing to accept them.

Boilers can be a subject which arouses passions in our hobby; we all have our own prejudices.

I read the very interesting article about the boiler for John Heald’s Darjeeling B class.

Once he realised the size of the boiler, the question: What would be the most suitable material to use?

Their answer was Duplex 2205.

After assembling a team of experts they designed, manufactured and tested the boiler in compliance with the then 2205 code.

The conclusions reached by the boiler test group are that a SAF 2205 Duplex boiler constructed to the AMBSC part 4 code for miniature boilers will be more than satisfactory provided the overall design and welding procedure is strictly adhered to. The life expectancy of the Duplex material SAF 2205 alloy steel should be similar to a copper boiler, and is suitable for boilers ranging from 25 – 50 litres (6 to 13 gallons).

Seeing as the Australians have a code 2205 which has been very thorough in its conception, why re-invent the wheel.

The difficult job will be first, coming to agreement with the AMBSC, then convincing the model engineering federations, plus the boiler inspectorate, the insurance companies, and the clubs to accept the new code.

I would imagine the specialised skills required to manufacture and test these boilers would need to be developed, but will present no problems.

We already have very good steel, and copper boiler manufacturers, I can’t see a reason why there should be a problem with Duplex steel.

I am not sure of the cost to have a new design of steel boiler passed for manufacture.

At the present time I believe we have nothing in place to satisfy the requirements for Duplex 2205 boiler manufacture, but I know there are people with the necessary knowledge who are investigating the

I think a better line of approach would be to push the association & federation about the issue.


Joined: 1-01-97

Topics: 9

Replies: 13

Posted: Fri 7th Nov 2014, 12:11pm

After my posting I was concerned, as it did not answer the questions that were posed by both Ian & Rob.

To answer Rob’s question “Has any further advancement been made in the use of Duplex steel for model locomotive boilers”

The answer to this question is yes.

The ongoing use of already existing Duplex steel boilers will produce a track record which will become an empirical treatise on which all concerned can base future decisions. I know this does not help your current requirement for your Thomas II boiler, but can only be considered as an ongoing step to further the knowledge about these boilers in use.

I find it is difficult to answer the Question asked by Ian “Can somebody out there suggest how we can move forward on this?”

It is difficult to ascertain exactly why we have no code covering the manufacture of boilers other than regulations and recommendations of guidance. I do believe there is a general reluctance to produce over bearing information covering this subject. To produce or even borrow an existing code for the manufacture of Duplex steel boilers could promote a response from insurers to produce a code of manufacture for both copper and mild steel boilers; this may be an area of concern.

When you consider the greater majority of models in the UK are constructed using copper boilers then the demand for introducing a code for Duplex would be in the minority. When a boiler group or committee meet to discuss such issues what priority Duplex has maybe the reason as to why there have been no steps forward in the UK.

To try and answer Ian’s question constructively, I believe it would require something along the lines you have already suggested Ian, using a group of people with the same common interest.

Have you established how many people share your thoughts?

Clearly the main barrier to using Duplex steel is general acceptance, the lack of insurance, also testing procedures and the necessary people to perform that task.
It would be easier with a group of likeminded people to establish what will be necessary to meet these requirements.

The boilers for a C19, a Thomas II, and a NG6 could be made in copper but at what cost, have you tried to approximate the cost between copper and Duplex 2205 for engines of this size?

On larger locomotives than mentioned it becomes impractical to produce copper boilers that are constructed using the model engineering methodology (copper silver soldered).
Boilers constructed for 4” & 6” scale prototypes are generally steel, so the group of people wishing to use Duplex does not necessarily need to be restricted to either 7 ¼” or railway engines.

Why not find how many people are interested, get together and form a Duplex boiler group. The objective of the group would be to introduce in a formal manner the use of Duplex steel for model boiler construction in the EU.
I am sure you will find many people with your interest, and many people with the required knowledge to help. Also you may find some who don’t share your view.

I hope this has been more positive than my previous posting



Joined: 1-01-70

Topics: 1

Replies: 14

Posted: Tue 11th Nov 2014, 6:42pm

In October 2014 The President of MEANZ , Model Engineering Association of New Zealand Inc , Richard Lockett, has issued an update on Duplex Stainless Steel and has stated that
" With the failure of the AMBSC Code Part 4 to be formally included in the Approved Code of Practice for Boilers New Zealand using the process available to us, the question is where to now for the use of this material within the hobby in New Zealand?
It is unfortunate that the AMBSC in the development of their new Code Part 4 Duplex Steel did not seek to attain an independent Design Verification, (DV) as this would have made the acceptance of the Code Part 4 by Government / state regulatory authorities around the world easier.
For us to be able to use Duplex Steel for the construction of our Boilers , its use has to be included into the Approved Boiler Code of Practice NZ which Codes Part 1 (Copper) and Part 2 Steel currently reside.
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