Pennsy Belpaire Boiler roof sheets....

jim templin · **Posted:** Wed Apr 21, 2010 12:13 am

As I understand the problem with the hashed to death K 4, and G series ten wheelers, is the roof sheet over the firebox was too thin from new. Is this the case, or have I misunderstood the problem. It seems to me that they likely had some pretty good mechanical engineers at Altoona. Are the original calculations around to see how this was figured, or is empirical evidence being sacrificed upon the alter of theory? Were roof sheets blowing off boilers on the Pennsy at alarming rates? I do know that there was some *ahem* trouble with inspectors wanting new, thicker dome lids on some engines, that had successfully been using the ones already there since new....

R L Musser · **Joined:** Fri Mar 12, 2021 8:30 pm **Posts:** 0

This is my post from August 7, 2007;

Quote:

To answer the questions on the roof sheet, there are several things to consider.

As far as the K-4 is concerned, we feel pretty confidant we figured out what the Pennsy did. When the earlier Belpare boilers were built, they were designed to have the crown/roof sheet bolts thread through the roof sheet and stick out enough to be able to thread a nut on the ends as well. When you use nuts that bear against the sheet you can use a thinner plate than you can without them. This is because you have not only the threads through the sheet as an attachment, but you also have a nut holding the sheet as well. This type of construction allows for a higher “constant” to be used in the flat stayed surface formulas in the ASME Locomotive Codes. The higher the constant, the thinner the minimum required thickness.

The Pennsy at some point (1940 +/-) eliminated the nuts and went with the bolts threaded into the sheets only method, presumably to save on costs. Everything we’ve seen so far indicates that they kept the same bolt pitches and didn’t make the sheet thicker to make-up for the lower constant. How they got away with it regulatory wise I don’t know, but in actual practice it worked. We went back as far as the 1920s era Locomotive Codes and couldn’t make it work. This particular calculation changed very little up to and including the last Loco Code of 1952.

The K-4 and most other Pennsy engines before the 1940s were built with 3/8” thick roof sheets. With the 5.0625” transverse bolt pitch, and 3/8” thickness, this gives a working pressure of only 175 psi for a 205 psi boiler. This isn’t even considering normal wastage which has made it even thinner. When you use the constant for nutted construction, you get a working pressure of 210 psi. This is one of the “design flaws” that Mike Tillger talked about.

This is where you get to the debate of “it worked before so why mess with it”. The problem is that you have to be able to hang your hat on numbers that support using a given part. If you can’t do that, then it’s all over and you replace the part.

I hope this helps,

R L Musser

As far as the dome lids are concerned, they don't get replaced because of inspectors. They get replaced because the calculations say they need to be replaced.
Almost anyone who has had to remove a lid will tell you that many times you have to bend the studs toward the center of the lid to get it off. That is because of the bending action caused by the moment arm. In other words, with the studs outside of the gasket, the lid will bend if it is not thick enough which will in turn will bend the studs as they are tightened.

jim templin · **Posted:** Wed Apr 21, 2010 12:50 am

Thanks for the Pennsy info...as for the dome lids, I have removed ALOT of them, and never had to bend a stud in any direction to get any of them off. Guess we have been lucky. Along those lines, has there been any record of a properly secured dome lid blowing off?

tomgears · **Posted:** Wed Apr 21, 2010 1:55 am

This is great information. Thanks for (re)posting. I guess when you call yourself "The Standard Railroad of the World" for a really long time people started to believe it and not question the engineering department.

Hillcrest · **Posted:** Wed Apr 21, 2010 2:11 am

Mr. Mussers' explanation of the PRR Belpair roofsheet should be posted automatically whenever the 1361 is mentioned....I also like it since it incorporates "wastage",a word I used to describe the deterioration of steel, after which I recieved a great deal of flak and was accused of using poor grammar...

Cheers, Dave

R L Musser · **Joined:** Fri Mar 12, 2021 8:30 pm **Posts:** 0

Jim,

Every one of our engines had the bent stud problem and I know of many other outfits that had them as well. In fact, just yesterday I calculated one for a customer that was too thin. That being said, there are engines out there with sufficient thickness to where bending is not an issue. The problem is not that they will blow off or they can’t withstand the pressure, it’s the bending of the lid and studs from tightening that is the problem. The concern is with the repeated bend cycles weakening the materials.

JimBoylan · **Posted:** Wed Apr 21, 2010 4:15 am

Would longer bolts with nuts on the rebuilt K-4 solve the problem of the "thin" sheet?

R L Musser · **Joined:** Fri Mar 12, 2021 8:30 pm **Posts:** 0

JimBoylan wrote:

Would longer bolts with nuts on the rebuilt K-4 solve the problem of the "thin" sheet?

It would to a point, but you still have the wastage problem which would only allow a MAWP of around 185 lbs. As we worked things out, using nuts with a new 3/8" sheet gave us 210 psi. The bottom line is that you have to replace all of the bolts regardless of the direction you go. Given the corrosion already there, it is the wise move to replace the sheet as well so you can operate the engine at it's designed working pressure.

Rick

jim templin · **Posted:** Wed Apr 21, 2010 6:47 pm

R L Musser wrote:

Jim,

Every one of our engines had the bent stud problem and I know of many other outfits that had them as well. In fact, just yesterday I calculated one for a customer that was too thin. That being said, there are engines out there with sufficient thickness to where bending is not an issue. The problem is not that they will blow off or they can’t withstand the pressure, it’s the bending of the lid and studs from tightening that is the problem. The concern is with the repeated bend cycles weakening the materials.

At the risk of being shot shot as an un American subversive, I always liked the continental practice of the whole dome being removable...beats standing on yer head to work on a throttle.....

J.B.Bane · **Joined:** Wed Aug 25, 2004 9:53 pm **Posts:** 68

So, it you put a nut on an extended staybolt rather than peening it tight, how do you avoid it leaking through the threads and between the nut and the sheet?

Newriver400 · **Posted:** Wed Apr 21, 2010 9:12 pm

J.B.Bane wrote:

So, it you put a nut on an extended staybolt rather than peening it tight, how do you avoid it leaking through the threads and between the nut and the sheet?

Isn't there special bucking/caulking tool that is used for this? Been a long time since I studied this aspect of boiler construction. Perhaps Rick or someone else can help clarify if I am correct.

I have my own questions regarding the subject. I spent some time writing a message earlier only to have the server connection lost, and thus the message went "poof." Rick, do you recall the factor of safety based on the roof sheet and staybolt combination as is at MAWP? Although it's obviously not 4, it would have to be well above 3, I'd think. Also, I agree that to correct the issue requires changing all of the bolts so installing a new, thicker roof sheet is sort of a no-brainer as the bolt work is a major part of the job. What about going ahead and changing the crown sheet as well? At least then you'll get another lifetime out the job based on the better care and less use that most steam sees nowadays.

Speaking of that, why not just derate the boiler to get the engine(s) out to generate at least some revenue and goodwill, then take care of the big fix at the next 1472 inspection? It's not as if any of the three under restoration are going really need that additional bit of horsepower for most any use they would likely see.

Just a few thoughts for discussion...

Best,
Mike

R L Musser · **Joined:** Fri Mar 12, 2021 8:30 pm **Posts:** 0

Newriver400 wrote:

J.B.Bane wrote:

So, it you put a nut on an extended staybolt rather than peening it tight, how do you avoid it leaking through the threads and between the nut and the sheet?

Isn't there special bucking/caulking tool that is used for this? Been a long time since I studied this aspect of boiler construction. Perhaps Rick or someone else can help clarify if I am correct.

I have my own questions regarding the subject. I spent some time writing a message earlier only to have the server connection lost, and thus the message went "poof." Rick, do you recall the factor of safety based on the roof sheet and staybolt combination as is at MAWP? Although it's obviously not 4, it would have to be well above 3, I'd think. Also, I agree that to correct the issue requires changing all of the bolts so installing a new, thicker roof sheet is sort of a no-brainer as the bolt work is a major part of the job. What about going ahead and changing the crown sheet as well? At least then you'll get another lifetime out the job based on the better care and less use that most steam sees nowadays.

Speaking of that, why not just derate the boiler to get the engine(s) out to generate at least some revenue and goodwill, then take care of the big fix at the next 1472 inspection? It's not as if any of the three under restoration are going really need that additional bit of horsepower for most any use they would likely see.

Just a few thoughts for discussion...

Best,
Mike

There is a tapered copper “washer” that goes against the roof sheet and around the bolt. A closed nut (similar to an acorn nut) threads on the bolt and compresses the washer against the sheet and the bolt thus making a seal.

I don’t recall the specific factor of safety on the roof sheet for either the G-5 or the K-4, although I think it was somewhere around 3.7. The bottom line is that you wouldn’t be able to operate either locomotive at its designed operating pressure. Yes, you could operate them at a lower pressure, but in my mind, if you are going to do a rebuild, you shouldn’t cut corners as it will come back to haunt you later. In these cases, you have to completely strip the back end of the boiler, including the cab to do this work. Since they are already at that point, now is the time as that would be a lot of extra expense in the future.

On the G-5, we did cut out a 2’ x 4’ section of the crown sheet that had a lot of stress corrosion around the bolts. Otherwise, the rest of the sheet is in very good shape.

Rick

Newriver400 · **Posted:** Thu Apr 22, 2010 10:18 am

I realize the law is clear on the required factor of safety, but from a purely theoretical point of view, actual failure is not an issue. Do you agree with that assessment? One other thing - the outside corners of the Belpaire are gonna be no easy task to fabricate. Is it possible that they are thick enough to reuse and what evidence of stress did ya'll find on the G5?

I'm guessing Altoona did the job with a die and a flanging press since they were in the mass production business, so I'm not sure how that would affect the flowing that is characteristic of flanged corners. Thanks for any info that could shed some light on the subject.

Best,
Mike

Kelly Anderson · **Joined:** Tue Sep 14, 2004 7:52 am **Posts:** 2477

Newriver400 · **Posted:** Thu Apr 22, 2010 10:40 am

Kelly Anderson wrote:

Rick had to take off, but like the White House Press Secretary, I’d like to “clarify” what he meant to say. The roof sheet on #1361 calculated out to a MAWP of approximately 155 PSI. For a boiler meant to hold 205 PSI that amounts to a F of S of 3.0, only 75% of what it should be.

Unlike the current White House Press Secretary, you can construct a cohesive sentence other than "I'll have to get back to you on that."

That said, did the G5 calculate out much different? Derating to 175 could be argued, but to 155 is really not - I'd go for the repair as well. I guess you could jeeringly say at 155, it's not much more than a really expensive coffee maker! :-p

Thanks for the info, Kelly. Please give my regards to Mr. Plaastead (I don't think I got the spelling right). Haven't seen him in many moons.

Best,
Mike