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.

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.

As to "nominally", have you ever worked on am old boiler? Everything about it is nominal.

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.

[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.

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.

This is written from home w/o any code books in front of me, so forgive any incorrect answers.

IIRC three types of staybolt attachment are allowed, threaded, full penetration welded, and fillet welded.

1. Threaded bolts are just that, you start with an undersized hole, and the reamer/tap opens it up to the root diameter of the thread and threads it. You screw in the bolt, leaving 3/16” protruding on each end, and optionally seal weld at least the fire box end of the bolt, then you drive the bolt with an air hammer, with a helper holding up a “bucker” on the opposite end to take some of the shock off the threads.

2. Full penetration welded bolts have a machined countersink cut into each outer surface, perhaps 80% of thickness of the sheet. The hole at the bottom is made 1/16 larger than the bolt so the molten root weld bead can flow through to gap at the water side to the sheet to produce a flush or convex bead around the bolt at that point. In reality though, the vast majority of full penetration welded bolts stop short of being true full penetration, leaving “valleys” on the water side and undercuts on the staybolts to corrode and be stress risers. From a practical standpoint, full penetration welded bolts are the worst of the three choices in that the countersink is large enough to be extremely difficult to cut with portable tools in the firebox during repairs. This difficulty results in shortcuts being taken such as the countersink being cut with a torch, etc. Also, full penetration bolts leave no “hole” in the sheet to cut to when replacing a bolt, since the bolt and the sheet have become one. That makes it very easy to end up with a ragged hole in the wrong place when trying to cut a broken bolt out.

3. Fillet welded bolts also have a 1/16” larger hole so the bolt doesn’t contact the side of the hole and is therefore technically longer than a threaded or full penetration bolt. Longer is better because the bolt doesn’t need to bend as much as the boiler expands. Also, the fillet welded bolt leaves the hole intact when cutting out a broken bolt so its proper location isn’t a mystery. Another advantage is that when the bolt is cut out, you are left with a true hole ready for the new bolt, with no need to create a large countersink. The replacement bolt can be a plain rod with a telltale drilled in it, no need to thread a new bolt. All of those advantages make for bolts that are the easiest to change of all three types (at least as long as you have a certified welder on staff), so poorly equipped operators have less need for trepidation when bolts need to be changed (a certified welder working out of his truck can do the job), and hopefully will not defer staybolt maintenance when needed.

If I recall, the codes want any threads removed as part of the weld prep prior to welding in a staybolt (or other part). Accordingly, the threaded staybolt that is welded in in the report photo is incorrect as well.

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?

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

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?

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

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!

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.

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.