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Welded Stays?
https://www.rypn.org/forums/viewtopic.php?f=1&t=45074		 Page 1 of 4
Author:  Great Western [ Sun Dec 06, 2020 8:50 am ]
Post subject:  Welded Stays?
Aside from the controversial issues, going back to a post on page 7 of the K&T 14 Case thread.

"Case 01-19-0002-2727, Exhibit 21 Sobczynski's Evaluation"

The rules governing rigid stays are confusing to me. The use of a combination of threading and welding is understandable. However, it states: The hole through which the staybolt is inserted shall be 1/64 to 1/16-inch larger than staybolt head diameter. The finished holes shall be true, cleaned of burrs, and nominally coaxaxial. The staybolt should be nominally centred in the hole.

So? What is the point of the bolts being threaded? This entire code, with words like "nominally" seems to be rather disturbing. Was this some sort of compromise approach by ASME?
If the holes are "coaxially" true, then it would seem that a hole of near interference fit would be desirable without threads. The holes would be expanded at the welded ends to receive weld material.
Perhaps I am missing something? Are the holes opened wider so that the welded filets are carrying the load, leaving the stays room to "flex"?
It would seem that a properly threaded and fitted stay with mechanically sealed ends would be more desirable than the above mentioned welded procedure. It would certainly be an easier repair for the next person in the future.
When did "nominal" enter into boiler building/repair practice? Why did it enter the lexicon?
Thank you for any help.
Author:  John T [ Sun Dec 06, 2020 11:51 am ]
Post subject:  Re: Welded Stays?
Why would you thread stays you are going to weld? Thread roots are an unnecessary stress riser in the stay and the sheet. Welding is faster and cheaper than threading.
Author:  John T [ Sun Dec 06, 2020 11:55 am ]
Post subject:  Re: Welded Stays?
As to "nominally", have you ever worked on am old boiler? Everything about it is nominal.
Author:  Dave [ Sun Dec 06, 2020 12:42 pm ]
Post subject:  Re: Welded Stays?
Threaded stays have been seal welded for decades now. Full penetration welded in stays without threads also. I've had better luck with FTP welded in stays in hard mountain railroading. Your mileage may vary.
Author:  mjanssen [ Sun Dec 06, 2020 1:53 pm ]
Post subject:  Re: Welded Stays?
[quote=If the holes are "coaxially" true, then it would seem that a hole of near interference fit would be desirable without threads. The holes would be expanded at the welded ends to receive weld material.
Perhaps I am missing something? Are the holes opened wider so that the welded filets are carrying the load, leaving the stays room to "flex"?
.[/quote]

The staybolt grows from the heat of welding faster than the hole in the sheet and the induced stress of this plastic deformation leads to radial cracking after a period of time in service. Similar observations have been made by Greenslade (Flannery) as well as others (Tross) on threaded bolts with seal welds. Providing a sufficient clearance for growth around the entire diameter has been found to alleviate this issue.

Most staybolt body failures exhibit cracking which when mapped, often reveal a direction of bending towards gathering in the middle lower or hot zone of the sidesheets as these sheets shrink from service. The longer the staybolt is, the lower the bending angle and the more length this bending stress can be distributed over to reduce the stress that any particular cross-section along the body must take. Lowering the specific staybolt stress towards all cross sections being only elastically loaded increases service life.

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Author:  Great Western [ Sun Dec 06, 2020 3:40 pm ]
Post subject:  Re: Welded Stays?
To mjanssen, thank you for the reply. That makes sense. Stehbolzen eh?! Alles ist gut, danke!

Dave, I get welding in the threaded stay ends rather than bucking them over. However, bucking them over might make life nicer for the next poor sap who has to take them out. As you say, though, certain circumstances call for different techniques.

John T. That is why I was asking about having threaded stays and over-sized holes as cited in the report from the K&T 14 thread. Makes no sense to me.
One definition for "nominal" is, "in name only." I have worked mainly on internal combustion engines. Torquing head bolt nuts to nominal values, as an example, does not cut it. One torques to defined values and owns the equipment to do that. I have not done a lot of work on heritage boilers, but some. Have done many threaded stays. The work was done to correct values with the proper tools.

I have known men who can use an acetylene torch with considerable skill and steadiness of hand. That said, torch fitting, in stay bolts, might be considered "nominal" work.
Accurate hole centering, drilling, reaming and threading, would be much better than "nominal."
The ASME rules expressed in that other thread just seem a little confusing -- to me, at least.
Thank you gentlemen.
Author:  Kelly Anderson [ Sun Dec 06, 2020 3:49 pm ]
Post subject:  Re: Welded Stays?
.
Author:  Great Western [ Sun Dec 06, 2020 4:06 pm ]
Post subject:  Re: Welded Stays?
Mr. Anderson, thank you. That is a very clear description of the options.
Perhaps the fault is mine in not being able to clearly decipher the section from the other thread. Perhaps the picture with the new stay threaded through part of the stub from an existing stay through me off?
Author:  Robby Peartree [ Sun Dec 06, 2020 6:20 pm ]
Post subject:  Re: Welded Stays?
Hi All

Three previous threads that tie into this discussion.
Technical Questions
viewtopic.php?f=1&t=22217
From the TRAIN News Blog (Re: New Locomotive Boiler Code)
viewtopic.php?f=1&t=28659
Wavy Side Sheets
viewtopic.php?f=1&t=31709&p=161424#p161424


Robby Peartree
Author:  adammil1 [ Sun Dec 06, 2020 9:34 pm ]
Post subject:  Re: Welded Stays?
With a fillet weld I am assuming that getting to the waterside would be impossible in most circumstances so the weld would have to be done only on the fireside and outside of the boiler only. Wouldn't there be a concern about waterside corrosion working its way back down the gap between the hole and the staybolt as well as fire side erosion possibly cutting back against the fillet and reducing it to an unacceptable thickness? I

Wouldn't this make the argument for threaded connection or full penetration welds are the preferred method? Am I overthinking this one and in practice these issues aren't as bad as they sound?
Author:  Kelly Anderson [ Sun Dec 06, 2020 9:56 pm ]
Post subject:  Re: Welded Stays?
.
Author:  Robby Peartree [ Mon Dec 07, 2020 12:12 am ]
Post subject:  Re: Welded Stays?
Kelly Anderson wrote:
adammil1 wrote:
Wouldn't there be a concern about waterside corrosion working its way back down the gap between the hole and the staybolt as well as fire side erosion possibly cutting back against the fillet and reducing it to an unacceptable thickness? I

Wouldn't this make the argument for threaded connection or full penetration welds are the preferred method? Am I overthinking this one and in practice these issues aren't as bad as they sound?
Full penetration bolts that aren't really full penetration (most of them) have the same issue with corrosion, as do threaded bolts that don't have the threads expanded through the full thickness of the plate (most of them).

Regarding fireside erosion, being that the weld it so accessible, adding weld to the eroded side of bolts as needed is not a major project.


Crevice corrosion is a real problem with fillet welded bolts along with thinning of the side sheets due to the gap between the sheet and the bolt and the weld being thinner in thickness, if you look at page 3 of technical questions thread you can see my post addressing this very issue. It seems that those who have not studied crevice corrosion refuse to see the issue.

Robby Peartree
Author:  Great Western [ Mon Dec 07, 2020 8:18 am ]
Post subject:  Re: Welded Stays?
Thank you all for the helpful information in this and the linked threads. We have a project coming up, hopefully next year, that will involve plenty of stay work. The plan is to do threaded stays as much as is possible. That will depend on securing the correct tooling for the longer stays. It will be done under the oversight of a provincial authority that works under the standard codes.
We want to do it right!
Author:  John Risley [ Mon Dec 07, 2020 10:27 am ]
Post subject:  Re: Welded Stays?
I think this is an informative thread and glad to see this type of thread. Which might educate someone a little or strengthen ones concepts of how and why we have staybolts and their purpose.

Do any of you more knowledgable boilermen care to explain the accepted here in the USA by FRA, using the "button" {forgive me I don't remember the name, slang or otherwise} for enlarged stay bolt holes when you want to shrink the diameter down closer to what was probably spec originally. After so many replacements the hole becomes enlarged to the point of needing to be shrunk back down to say 7/8" from 1 1/4 or larger. Think some of the large roads like UP used these? Alternative to welding up the hole and redrilling. Hope my not so great explanation is enough to get to what I am trying too?

It has been a while since I saw these in use during repair. Think they are installed from the water side wrapper sheet and seal welded in place. These to my knowledge are not used on the side sheets that would probably be replaced if things had deteriorated this far?

Thanks in advance. Blessings, John.
Author:  Howard P. [ Mon Dec 07, 2020 10:53 am ]
Post subject:  Re: Welded Stays?
John,

What you are referencing are "sunflowers" as some call them. Welded-in bushings to get a a few staybolt holes down to a reasonable diameter.

Howard P.
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