Steel Specifications for Boilers

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Dan Rowe

Well-Known Member
Feb 12, 2010
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The AMBSC is a very good reference for boilers but some of the specifications are not easy to find in the US where the ASME boiler code is used by most of the States with some exceptions for hobby boilers. The price of the ASME code is well beyond the means of most hobby builders.

Here is a thread for US State boiler code information:

Marty Knox is a very experienced boiler maker and he has written several good articles on boilers for live steam magazines. Here is a link to one of his posts on this subject.

Here is most of his first post and one further into the thread that lists the ASME steel types both written by Marty Knox:

"My comments are based on 30 years of building, inspecting, operating, and maintaining boilers.
The first quality of a boiler material that comes to mind is ductility - you want a material that will withstand many,many heating and cooling cycles, with out fatiguing and cracking. Strength is almost secondary - the strength of a boiler is in its structure. Up to about 5 1/2 - 6" diameter and 100 PSI copper has many advantages,above that,low carbon steel is the material of choice. I worked as a boilermaker for DuPont. They have a whole department that works on material specifications. They never hesitate to buy the best material for the application. We worked with a wide variety of materials - Inconel, Hastelloy, and Carpenter 20 to name a few - yet all our boilers were low carbon steel!"

ASME code vessel
Shell - SA106 B
Plate - SA285 grade C/SA515 grade 70/SA516 grade 70
Steel Tubes - SA178 grade A (welded) SA192 (seamless)
Copper Tubes - no Code specification
Staybolts - SA36/SA675
Threaded couplings - SA105 3M (3000#)

Now back to the AMBSC Code which is well worth getting because it has many drawings and descriptions of welding procedure required for a steel boiler.

The steel specifications listed in the AMBSC Code Part 2 Issue 4 - 1995 are:
Steel pressure vessel plate AS 1548 all grades
Steel sections and bars AS 1442 grades CS 1020, K1020, S 1020
Seamless steel tubes ASTM A 106, ASTM A 53, BS 3601 grade 360
Welded steel pipe ASTM A53, BS 3601 grade 360 ERW
Pipe fittings BS 1740

Boilers are to important to simply use what ever steel is handy in the scrap pile so hopefully this thread can help.

Dan, Your quite correct on the materials. In Alberta Can. where I am if you want your boiler passed, it has to be built from ASME code materials with full documentation on each piece. While the AMBSC code book makes allowances that pertain to our smaller models, it only allows materials like the ASME codes far as I know. John
Dan I stand corrected. I see that the Australian materials such as AS 1548 don't unless it's been changed meet the ASME code requirements. Interesting. A person definately has to check the local codes where you live. John
Prospect said:
A person definately has to check the local codes where you live.

Yes that is the first thing to check when starting a boiler design. You should also check who does the inspections if any are required locally. I worked as a marine engineer which is ASME code and we were inspected by the USCG and ABS.

Hobby size boilers are not really covered in the ASME code but if it is required where you live then the rules apply and ALL material specifications and ALL construction and design rules apply.

This thread was started in response to Brian's post.

te_gui said:
1020 is a low carbon steel, can certainly take lots of pressure cycles, based on my hydraulic experience.My only question would be the heating/cooling. It has a similar carbon content to the A53 spec you referenced, so potentially about the same ductility. The pipe spec didn't give a % elongation which would help equate the two materials better.

I'm a mechanical engineer by education and experience, but not a boiler maker. I might mention as a side note, I helped restore a full size Willamette logging donkey and ran the calculations necessary to get the boiler certified here in Washington by the state boiler board, but that had more to do with the existing material thicknesses and riveted joints.

I'm curious about the Australian materials, I should get a copy of their code. My company has a plant in Brisbane, with a full engineering staff. I could probably get some of the Australian material specs crossed into US or ISO material equivalents with my colleagues assistance down under if there was interest.


I am very interested Australian material specs and would love to know the equivalent US or ISO material specs. This would not make the AMBSC a legal code where I live in central Texas but it would be a complete set of design rules with a proven track record.

The size of boilers I am planning are exempt from the Texas code. I want to have the proper metal with stamps and paper trail even if it is not required before I look for a welder.

I found a link for steel sections and bars AS 1442 grades CS 1020, K1020, S 1020. Technical Handbook Iss3.pdf

The CS. K and S designations are the degree of deoxidation they are in table 7.
Table 9 is the nearest equivalents for other country codes.

ASTM 1020
UNS G10200
BS970 070M20 old En3B

I could not find a similar table for AS 1548 which all grades are fine for the AMBSC. I did find an article stating that the AS 1548 pressure vessel plate has been accepted by the ASME and was listed in the 2003 standards. See page 3:

Edit: Here is an over view of the AS 1548 standard and photos of the grain structure as rolled and during an after annealing. This is very interesting data that shows that just any old chunk of steel is not suitable for boiler fabrication.


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