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The ''S'' stamp
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Brian Harris and a completed boiler for a 60 HP Case
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The firebox being carefully set down into place in the boiler shell for a 50 HP Sawyer-Massey.

Over the past nine years that my son, Steve, and I have taken
our steam traction engines to shows, we have spoken with many
people about the new boilers we’ve built and installed in our

The September/October 2003 issue of Steam Traction
carried my article ‘Steaming Through Life,’ in which I
discussed my history in steam and my current steam projects,
including building new boilers. We have received some really great
feedback from that article, including many questions about making
new boilers.

Looking back at the most commonly asked questions, there appear
to be some myths and misconceptions about boiler facts. Possibly
this is a result of information being passed down through
generations of collectors, and of course there’s the fact that
standards have changed since most of our boilers were originally
built. Manufacturing methods and materials have evolved a great
deal since the days when everyone drove Model Ts.

I am retired, and I no longer build boilers or have any
affiliation with any boiler shop. Even so, I’m often asked to
recommend a good boiler shop, a question whose answer I can
certainly appreciate. I would instead, however, like to give some
sound information and facts to help people make their own decisions
about who they hire to build a boiler.

The following information is documented in the American
Society of Mechanical Engineers
(ASME) Power Boilers
a publication every certified boiler shop has to
follow. Additionally, much of this follows the normal manufacturing
standards, practices and requirements imposed by New York State
Board of Labor Boiler Inspectors. For many readers this will be a
very dry article, but if you are thinking of having a new boiler
made, the information could be very beneficial.

A 60 HP Reeves engine and gearing assembly mounted on a
partially completed boiler shell. This initial fitting was done to
ensure that necessary studs were properly located and capped on the
inside and to ensure that all the major parts and gearing were
properly located and meshing correctly.


1. Contact your state boiler inspector. It is in your best
interest to keep your inspector informed of your intentions before
you do anything. Keep your inspector on your good side by keeping
him up to date. Let him look everything over before you start
calling him when the work is complete is the wrong approach. An
inspector will not want to pass something without knowing what went
into it.

2. The boiler has to be built to the latest ASME codes and have
an ‘S’ stamp. For manufacture in New York State, it must
also be stamped and registered with a national board number, check
with your state inspector.

3. Thoroughly research the manufacturer or fabricator. Talk to
someone who has had a boiler built by this company and see if they
are happy with the results. See the work shop if possible and study
their craftsmanship. Most manufacturers will allow this, as they
want you to be happy with the finished product and send more work
their way.

4. Make sure you have a signed, written contract stating all
work to be done and the manner in which it should be completed.
Your contract should mandate that you receive a copy of the boiler
prints, proof of x-ray of the longitudinal seam of the barrel, heat
treatment charts and the manufacturer data report. Having a boiler
built is not like buying a car where everything is cut and dry.
Cars are mass-produced: one is the same as the next, you know what
you’re buying. With a custom-manufactured boiler, the only
proof you’ll have is documentation.

5. The ballpark price for a mid-size boiler (60 HP steam
tractor) should be around $25,000 to $30,000. If you get a quote
much lower than this, there is most likely some corner-cutting
involved and it could come back to haunt you later.

6. If a manufacturer claims they could save you money with a
boiler they already made that will fit your tractor be suspicious,
as this is highly unlikely. No two boilers were made the same: each
one was individually handcrafted.

Contracted crews that worked side by side in the assembly bay in
the factory built most traction engines. Each crew would start with
a boiler from the boiler department and obtain all the partially
finished parts from the machine shop, custom fitting, grinding and
drilling the parts to fit the particular boiler they were working
on. Mounting studs and pad locations were all unique. Each crew
would come up with their own practices, resulting in minor
differences between finished boilers.

You are now faced with the opposite task. You have all the
finished parts already drilled and shaped. Now you need to make a
boiler to fit those parts. For some designs this is not as bad as
others. If you have a boiler that is frame mounted, like a Frick,
you will only have to mate up a few key points. On the other hand,
when we fitted our Minneapolis there were 150 taped studs that held
the saddles and mounts onto the boiler. Every one of the mounting
studs has to be capped or have a backing plate. If using straight
thread studs, the holes cannot go all the way through into the

7. Do not buy a boiler that is stamped too much over the working
pressure of the original engine. The boiler may be new, but the
engine castings are still 80-year-old cast iron. A boiler made with
modern materials to the design of the original boiler could
possibly be manufactured and stamped for over 250 psi, and someone
could then put a 250-psi safety valve on the boiler. The
‘D’ valve and piston were not designed for this much
pressure and could blow apart. Another problem is the water-feed
injectors will not function properly at this high a pressure.

8. Some manufacturers use pipe couplings and plugs for
inspection openings and others use hand-hole covers. Both methods
are acceptable, and both have their advantages and

Couplings and plugs are less expensive to install initially, and
they don’t require gasket replacement every year. The downside
is that the threads will not last and eventually the couplings will
have to be replaced. Further, the hole is smaller than a standard
hand hole, making cleaning and inspection much more difficult.

Hand-hole covers are more difficult to install, they require
gaskets that need periodic replacement, and there is always the
chance of a gasket blowout. Code section PFT-43.4 calls for there
to be seven inspection openings in locomotive fire-tube boilers:
One in the rear head (smoke box) below the tubes; four in the lower
corners of the water leg; one near the throat sheet (when
possible); one in the front head (firebox end) at the line of the
top of the crown sheet; and one in the shell (barrel).

9. One of the issues we questioned consultants and inspectors on
was water feed inlets. Code section PG-61 states that if the feed
supply is interrupted one such means of feeding water shall not be
susceptible to the same interruption as the other, and each shall
provide sufficient water to prevent damage to the boiler. I was
assured that this meant two completely separate feed lines all the
way into the boiler. Many original boilers have two feed lines that
go into one inlet. This is no longer acceptable.

10. A vital issue with the boiler is the water level in the
boiler in relationship to the gauge glass. Code section PG-60.1
states that the lowest visible part of the water gauge glass shall
be at least two inches above the lowest permissible boiler water
level, as determined by the boiler manufacturer.

11. Another important issue is to ensure there is a suitable,
new, ASME-stamped fusible plug fitted at the highest point of the
crown sheet. While you are looking at the fusible plug, take a good
look around the firebox at the stays. Code section PW-19 states
that the ends of the stays inserted through the sheet shall not
project more than 3/8-inch beyond surfaces exposed to combustion.
This is because stays can, over time, burn. Also, look at how the
fire bars are going to be hung and the ash pan mounted. Will they
be able to be removed in a practical manner for cleaning and
inspection of the firebox?

12. Those of you wishing to preserve the original look of your
boiler by riveting sections together should keep in mind that
riveting has been excluded from the codebooks since 1971. Many
inspectors view riveting as an obsolete practice, and any rivet
work that is done has to follow the 1971 code. A good number of
mechanical engineers and inspectors have been born after 1971.

13. When installing a new boiler the most underestimated job is
refitting all the pipe work and accessories. Although the price tag
for this part of the project varies from state to state, it can
cost up to $3,000. In New York, everything has to be installed
using schedule 80 pipe, and everything has to be rated for at least
1-1/2 times the Maximum Allowable Working Pressure (MAWP). Our
boilers have a MAWP of 175 psi, which meant all of our valves,
checks, gauges and fittings had to be rated for a minimum of 300
psi. Some expensive valves such as the main steam shut off, blow
down and safety valve have to be purchased new. A new set of fire
bars will probably have to be custom cast. Sandblasting and
painting is going to be a time-consuming and costly item, and there
are always parts that need to be built up and repaired.


While the foregoing discussion doesn’t cover all the issues
surrounding the manufacture of a boiler, the points I’ve
addressed answer commonly asked questions. Getting a boiler made is
not something to just jump into, as there are many issues to be
considered. Be that as it may, the more informed you are, the more
successful you will be in getting a good, new boiler made, which,
of course, is the whole point.

The ASME and the ‘S’ Stamp

The American Society of Mechanical Engineers traces its roots
back to 1880 when it was established to encourage uniformity in
shop drawing symbols, pulleys and other mechanical elements used in

The ASME’s Boiler and Pressure Vessel Code was first written
in 1914 and has since been adopted by 49 states and Canada. Only
South Carolina has yet to officially adopt the ASME code.

ASME certification stamps contain a letter (and in some cases an
attendant number) categorizing the specific certification. The
stamps are a stylized four-leaf clover with the letter (and number)
contained within the clover’s borders.

For owners and operators of historic boilers, the most commonly
referenced ASME stamp is the ‘S’ Under ASME code, power
boilers generating over 15-psi steam, 160-psi water and temperature
exceeding 250 degrees F are required to carry the ASME’s
‘S’ stamp.

Contact steam enthusiast Brian Harris at: 3939 Upper
Mountain Road, Sanborn, NY 14132-9119.

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