LE Bronze and copper boiler pressure rating

[r2brick]

I purchased an unused LE bronze and copper boiler some years ago, the sales receipt from LE, in the former owner's name is dated 1974. My intention is to construct a test boiler fired on propane to test components for my 1.6 scale B&A 4-6-6T locomotive. What pressures, operating and test, would be safe for this boiler? The boiler is stamped, "Not for commercial use", across the back-head just below the top edge. The boiler shows now corrosion from silver soldering flux, etc. I did a water tightness test to 80lbs pressure, which proved a water tight boiler.

[Bill Shields]

Safe pressure is based on calculations from material, thickness, stay design, diameter and placement.

Beyond that, anyone who gives you another reply is making a dangerous guess based on no engineering fact.

The calculations are straightforward.

Several clubs have published their operating pressure calculation sheets.

[David Powell]

If you do the calculations you will have given yourself a starting point. That will be the THEORETICAL answer based on the strength of the materials used.
Then there comes the practical part of the answer. Look at the joints, do they look well soldered. You have already given it a hydro test and it shows no leaks.
Now comes decision time--- As an example only, Theory shows boiler could withstand 500 psi hydro pressure, without problems ie stresses all well within elastic limits of stays etc,, Bursting pressure in theory 700 lbs. you took it to 250 lbs hydro test and saw no leakage or distortion. You are happy with a safety factor of 4 so your working pressure can be at or near 60 lbs,
At that pressure, and indeed pressures beneath about 100 lbs the temperatures at which copper begins to lose strength need not be a cause for concern.
As a secondary look at a given boiler you might well look at other models of the same design and see at what pressure they are, and have been running at, and if there have been any issues reported.(For example LBSC's original Britannia 3 1/2in gauge boiler will experience distortion in the firebox and combustion chamber if hydraulic tested over 200 lbs) yet dozens of that design have run for 50 yrs or more safely at 80 lbs working pressure,
The final decision is, of course yours.
We do not need to be fearful, just respectful and knowledgeable.
Regards David Powell,

[Glenn Brooks]

As others have said, the weakest points in most boilers are the joint interface and crown sheet. Watch for water leaks or bulges at the joints and firebox sides. Also, you don’t need full operating pressure to test locomotive components. Most hobby locos will chug along quite nicely at 40-60psi…

One other really nice advantage for your proposed test boiler is to use it to steam bend wood. At 50psi you can pump low volume 200* steam vapor into a plywood steam chamber to prep all kinds of hardwood for bending. Great for bending roof carlines and all manner of arches and curved window trim - large and small. Works a treat.

Glenn