Related, possibly - Puffing Billy Railway.

The riveted boilers on the NA locomotives were customarily replaced with new riveted boilers fairly frequently - memory says 10 years of service, but i may be wrong there....so, sometime in the late 20th century they started building welded boilers rather than riveting them. Come the first life cycle changeout expected, they were pleasantly surprised to find out that only the firebox of the welded boiler needed to be replaced, the welded shell was still good.

What I don't know is how the welded parts were formed and joined. My guess is the corners were flanged at the throat and backhead and in the firebox, but I don't know about the dome, door hole and FTS. I've asked a friend from there to fill me in if possible. Maybe somebody here knows?

In any case, if I were to be building a new boiler today, I'd want to use flanged corners wherever possible and match the thickness of the materials to the specifications for the riveted original to the extent that it is possible. The 100% efficiency for the welded seams would just be additional margin from that perspective, and it would probably be considered overbuilt, but unless water quality or other issues were involved, i think it would lead to a longer in-service life made that way.

dave

Yes the PBR boilers do have rounded corners, a firebox door ring. Can't remember how the dome is mounted. These boilers are how welded boilers should be.

And in general terms that's how I would do a welded boiler with a few other things added in.

Under ASME are new, welded boilers required to be stress relieved? I had heard that this was no longer mandated but can't find anything on-line to verify this.
Thank you.

Not necessarily, Table PW-39-1 Mandatory Requirements for Postweld Heat Treatment of Pressure Parts and Attachments - P No. 1 General Note (a), "Postweld heat treatment is not mandatory for P-No. 1 materials under the following conditions: (1) when the nominal thickness of a weld as defined in PW-39.4 does not exceed 3/4in. and a minimum preheat of 200° F is applied when the nominal material thickness of any of the base metals in the weld joint exceeds 1in." P numbers refer to the chemical composition of the alloy being welded. P-No. 1 materials are carbon steel such as SA-285-C and SA-516-70, two typical types of boiler plate.

There are other exemptions for thicker welds and thick materials, but there are tighter restrictions.

It is important to understand the transformation base metals go through and the stresses induced by welding when making the decision to stress relieve (postweld heat treat) a weldment or not. I would certainly want to heat treat the firebox and wrapper sheets after assembly, all those staybolts will be under enough stress in service, no need to start life that way.

Mark, you referenced Scotch marine boilers and Morrison furnaces in the same post. Now I'm foaming, have lost all frame of reference and forget what this thread is about ...

Do not be mislead regarding Table PW-39. Post heat treat is still mandated for pressure vessels in general in the P-1 group. PW-39 lists a few exceptions and is very specific. For instance if there is a longitudinal seam you must heat treat. Fireboxes and wrappers are not excepted from heat treat. If you are contemplating construction of a new boiler using an "S" stamp plan to heat treat it.

Chris DeWitt

Respectfully, can you point me to the paragraph that requires all longitudinal joints in P-1 material be postweld heat treated? I am not saying it isn't there, only I have not been able to find it.

Thank you.

First of all the code is a document of exclusions. This means that if a detail isn’t specifically excluded in writing then all the general rules apply.

That said, reading PW-39.1, it says "Except as provided ... in the notes within table PW-39.1...all welded pressure parts of power boilers shall be given a post heat treatment at a temperature not less than that specified in table PW-39.1."

The notes exclude circumferential seams and tubes and sundry. There is not specific exclusion for longitudinal seams. Of course you can argue with your ASME representative but if you can’t point to a specific exclusion by name it’s a waste of time.

So the bottom line, saying “I didn’t see it in the code so I can do it” doesn’t work.

Chris De Witt

OK, so a new welded locomotive boiler (with nice flanged corners) should be heat-treated after completion. I seem to recall that Alco had the large heat-treating (annealing?) oven, and that was one reason Alco produced the welded boilers for post-1940 steam power.

With that large chamber gone, what would acceptable post-assembly heat treatment be? Strip heaters and insulated blankets ? That's what was used on submarine hull weld joints in 1974, USN 688-class boats. I still have my Tempilsticks somewhere.....

Howard P.

Seems like there is plenty of heat treating capacity around. Here are a couple of local firms that came up on a quick search:

http://www.ic.gc.ca/app/ccc/srch/nvgt.d ... 2&app=sold

http://www.aberfoyle-mt.com/

Thank you for the information re ASME requirements. Sorry if I have led this thread astray.

One other thing; If you think that the code is inadequate or doesn’t make sense, or you want to do something not provided for in the code you can ask for an interpretation by letter (appendix 1) They will reply and some are printed and distributed as an addendum to the code. Most of them make good reading. So there is recourse if you want to fight with them

While earning my BSME in the late 80's I was able to perform a FEA on a live steam boiler I designed similar to what would be found on a RRSC mogul, very colorful!
I was also able to perform a destructive tensile test on a 1.125 in. threaded staybolt. Percent elongation was nothing like the lab instructor had ever seen before and he was quite interested in what material it was as he had never heard of wrought iron before. We also cut and polished a piece to look at, again amazed lab instructor. We also tested the modern equivalent of staybolt steel, and it snapped with a with a hardy "ping"!! The wrought iron bolt came apart like laffy taffy.
A couple of years later I came to appreciate the ease at which wrought iron is to "work" with an air hammer. To bad you cant get it anymore.