I thought it might be a good idea to start a discussion of designing a locomotive boiler that is compliant with the current rules of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section I, “Power Boilers”. This is meant to be an educational discussion based around a hypothetical locomotive owner/user that needs to have a boiler designed and built to replace the one that has come to the end of its useful service life.

What is an ASME “S” Certificate? The ASME certifies businesses that wish to be compliant with the relevant sections of the Code for the work the business plans to perform. The ASME Code is an approximately 20,000 page document broken up into 12 Sections. The 12 Sections cover four major topics: power boilers, unfired pressure vessels, nuclear vessels and transportation tanks. Sections contain design and construction rules or supporting information about materials, welding, care and maintenance (though it should be said the National Board Inspection Code is usually the primary document for those activities) and nondestructive examination. The rules for the construction of locomotive boilers are found in Section I, “Power Boilers”. Businesses using this Section may hold one or more of the following ASME Certificates: “S” for the design and construction of power boilers; “A” for the assembly of power boilers (usually held by large engineering construction companies that erect power plants); “M” for the construction of miniature boilers; “PP” for companies that only want to assemble power piping (in general terms, the piping coming off the boiler up to and including the first valve); “V” for the design, manufacture and servicing of pressure relief devices for power boilers. To design and build a new locomotive boiler and certify that the boiler meets the minimum requirements of the ASME Code, a manufacturer must have been issued an “S” Certificate.

Before any design work can begin the customer needs to have a discussion with the manufacturer about the type of service the boiler will be in, what type of fuel will be used and how the fuel will be delivered to the firebox, problems with the design or functionality of the original boiler, any changes the customer may have in mind and anything else that may be relevant to the design, construction and use of the boiler. Perhaps one of the most important discussions between the customer and manufacturer is the regulatory agency that will be responsible for enforcing the regulations the boiler will be permitted to operate under. If the locomotive is owned by an amusement park and is not part of the national railway system, then the regulatory agency might be the local Jurisdiction or the government of the State the boiler will operate in. If the locomotive is to run on part of the national railway system, then chances are the regulatory agency will be the Federal Railway Administration (FRA). This is important to know as the different Jurisdictions may have additional requirements not covered in the ASME Code. It is important to remember that the ASME Code provides minimum requirements for design and construction, customer specifications and Jurisdictional requirements may be more strict and comprehensive.

The design package usually contains a drawing showing the layout of the boiler, weld details, materials and thicknesses, Code information, examination instructions and any other information the manufacturer’s quality control system requires. Along with the drawings are general notes, supporting calculations, bill of materials and a traveler. Different manufacturers document their work in different ways so they may not all be described here. All this information once complete and approved by the customer is then reviewed by an Authorized Inspector (AI). The AI is an individual that has earned a National Board of Boiler and Pressure Vessel Inspector’s Commission or has a Commission from a Jurisdiction or both. Since the customer requires the boiler’s Master Data Report be registered with the National Board, the AI must have a National Board Commission and an “A” endorsement allowing him to conduct shop inspections of new construction. The general policy of Authorized Inspection Agencies (the companies or Jurisdictions AI’s work for) is to “accept”, not “approve” design packages. This is an important distinction because it is not the responsibility of the AI to design a boiler, only to certify the manufacturer designed and built the boiler to the requirements of the Code and the manufacturer’s quality control system. In reality, manufacturers usually have a good working relationship with their shop AI so the collaboration usually is far more technical than simply checking boxes. Perhaps some of the AI’s that post on this site would care to elaborate on their shop experiences.

I wanted to give an introduction to the process so readers have an idea of the people involved in the design and construction process. Part of my intent here is to demystify the locomotive boiler industry a little bit. In my next post, I’ll have a hand sketch of the example boiler and start describing the relevant parts of Section I and how to apply the design formulas. I hope other Code users will post their opinions and correct me if I post questionable or downright wrong information.

Paul;
Excellent post. You are right on in paragraphs three and four. Section I is not going to tell you how to design a good locomotive boiler, and whatever you want to do in the code shop, the A.I. is going to have to sign off on it.
Following the Code, you can build a safe boiler, but it may not have a long service life. Longevity of the boiler goes back to good engineering and an understanding of the pressure vessels service requirements.
This brings to mind the problems of the Tornado boiler. While it is probably not going to blow up, it has a short service life. My suspicion is the "mud ring" term is a misnomer. The correct term should be "foundation ring". I suspect the firebox is not properly anchored, and is moving is ways that are not conducive to long staybolt and sheet life.

Great post. There have been a few locomotive boilers built here in the post steam era. An in-depth discussion of the engineers and regulatory process would be something well worth sharing here.

Greetings:
Indeed a great topic, thanks Paul!
Nathan brings up an excellent point: LONGEVITY.
It is possible to design a boiler which will meet all Code and Regulatory requirements yet provide for no wastage on parts of the vessel. That is, the moment it corrodes a fraction of an inch, it no longer meets the design criteria, therefore should not be operated at the design pressure, it should be derated.
Major locomotive builders in the steam era were guilty of this.
When we did the calculations for our first 1472 Service Day inspection on our No.40, we were rather shocked to find that the door sheet, originally designed with a 5/16" sheet, had no margin for wastage (and, trust me there was). We had to lower the operating pressure from 175 to 160 PSI until we renewed the door sheet.
We increased the thickness of the new door sheet to 3/8" (as per the rest of the firebox).
J.David

Which brings to mind another subject that might be included: major repairs to existing boilers requiring alterations. Bonding new and old materials and techniques to effect robust and legal repairs is a situation more of us are likely to face.

TVRM did a partial course replacement on 630 that qualifies - maybe Mark will share that story.

dave

Granted, it is not about an ASME boiler, but there is an interesting article in Heritage Railway #147 about 'Developing a modern locomotive boiler' by Alan Haigh. The author has also written a book titled 'The Design, Construction, and Working of Locomotive Boilers', which is available from Xpress Publishing.

Paul,

I think we've had this conversation before, but I thought there was some conflict in the ASME versus FRA boiler requirements so that it was very difficult to make a boiler complient with both sets of rules? Or am I confusing this with un-fired pressure vessels (Air tanks)?

Greg

Some time ago there was also a terrific post by one of the less frequent posting members who was a metalurgist I believe, and this member explained how the metallurgy used long ago in boiler sheets is very different from the metallurgy used now.

The steel we use now is much cleaner. That sounds good right, nope its really bad for our boilers. The newer boiler sheets rusts much quicker than the older steel and that changes everything.

Find that post and reattach it here, and that would add a great deal of info to this post.

.

The main difference between the ASME and the FRA regs pertains to the maximum allowable stresses for staybolts and braces. The ASME basically goes with a factor of safety of 3.5 for everything. The FRA states that the maximum allowable stress for staybolts is 7,500 psi and the maximum allowable for braces is 9,000 psi, regardless of the tensile strength of the material.

Rick

The ASME Code provides the minimum requirements for building a safe boiler. The word minimum is not meant to give the idea of inferiority, rather the foundation on which boilers and pressure vessels get built. Nothing can replace a good designer and fabricator with years of experience in creating vessels for the markets those individuals and businesses serve. Air tanks look simple, a shell, a couple of heads and some nozzles. What if that air tank is going into a new production line at an assembly plant and will have many pipes bolted to it? What if the tank is 6 feet in diameter and 20 feet high and installed in a zone four seismic area? All of those additional loads are not directly addressed in the Code. It is up to the manufacturer to know how to design for these additional loads and just as important, it is the responsibility of the customer to know what to ask for.

The FRA rules have additional requirements for locomotive boilers that will operate under the FRA's jurisdiction. There is nothing in the ASME Code that prevents a builder from applying the stricter requirements for boilers found in Part 230. However, it is possible to build a boiler that is not compliant with FRA requirements and this is where experience comes in. I don't mean to say that someone couldn't sit down and read the Code and Part 230 and design a compliant boiler, but if I'm a customer I wouldn't want to have to pay for the learning curve.

Most of my experiences with locomotive style boilers were with vessels not under FRA jurisdiction. I have read Part 230, I have a copy in my desk, but am not the authority some of the other posters on this site are. I hope as we go along in this discussion those individuals will comment on how to square Part 230 requirements with the current Edition of the Code.

Paul;
In designing a locomotive boiler, you have the A.S.M.E. requirements, the FRA requirements, and the final customer may have some special requirements. It is indeed up to the engineer of record to ensure all three sets of requirements are met, and to insure that they do not conflict with each other.
One thing the A.S.M.E. Code is not going to do, and that is become a book titled...
"Locomotive Boiler Design for Dummies!" It is up to the design engineers to know what they are doing.

Dear Loco112

You Stated “The steel we use now is much cleaner. That sounds good right, nope its really bad for our boilers. The newer boiler sheets rusts much quicker than the older steel and that changes everything."

Could you be so kind to explain how “cleaning the steel created the behavior difference you describe?

Robby Peartree

Often, certain parts of locomotive boilers were built with a factor of safety of 6....a few cases even 8 while the balance were all in excess of 4. It is important to understand that the ASME code does not account for boilers being a structural/load bearing component of the machine upon which they are mounted. Also, they do not account for rapid thermal cycles.
We have not become smarter than the people that historically designed locomotive boilers. I would say that rather than attempting to design a code boiler that meets FRA we should look at it from the vantage point of replicating (using the practice of welding of course) the original boiler in keeping with FRA/traditional locomotive standards. As a rule, a boiler constructed in keeping with original locomotive design practices will exceed all of the design requirements associated with ASME....unless it is a pennsy boiler ;).
IMHO it would be a bad practice to modify off of the original design simply because the locomotive is not to be under federal jurisdiction. Why weaken the boiler just because we can?
Lastly, as has been proven by the new boiler constructed now on the #3 in cali, a boiler for locomotive service under the FRA need not be constructed by an "S" stamp shop. It need only meet locomotive boiler design requirements and should be assembled with welding practices outlined in ASME code.

Cheers, Jason

If I could find that old post, and unfortunately Kelly's link is not it, you'll read that the old boiler plate had more junk in it, impurities and higher levels of unwanted elements, those actually prevented deep rusting. Thats the reason we have 120 year old boilers still running around at their rated or close to it, pressures, while the newer built boilers don't last anywhere close to that.

When I find that old post, I'll post it in this thread.