Yes, I meant stays necked by wastage.
In the one case, I don't think the inspector was working from any great technical understanding when he asked for some necked crown stays to be replaced, but it was his right to ask, and they did look poor. He had been pleasant and helpful on other aspects of the restoration, so that was fine.
He quit doing heritage boilers, and the inspector who finally did the certification was more than thrilled.

My reaction to this fiasco at this point is "a curse on all your houses": to Big South Fork Scenic Railway for wanting a cheepo return to service, and to the various contractors for shrugging and agreeing to it.

BTW this is an interesting thread.

Hey guys. Let's avoid the other issues or this thread will get toasted. Too much good info here to lose.
Thank you.

I want to be sure I understand a couple of code points completely.

First, the point about the fillet-welded staybolt is that the fillets take the full load, in tension, and that the thickness and profile of the fillets constitute the 125% of diameter area required for 'engagement'. There isn't supposed to be any contact between the metal bore of the hole in the sheet and the stay at all!

The first potential issue is that some positive means needs to be used to keep that 1/16" nominal gap concentric (i.e. the bolt precisely in the middle of slightly oversize reamed hole -- and it would be reamed, to match the machined surface of the bolt going through the plate, as there isn't any good way to 'gap' the hole to fit an irregular bolt other than via some tweak form of EDM). I suppose this could be jiggered to put the bolt closer to the edge on the opposite side from the direction it will supposedly be deflecting under thermal load ... but do we know this precisely enough when "in there" welding?

The second potential issue is that raised by Robbie, about the crevice corrosion that results from a fine gap (and a potential slight angling of the stay in the clearance hole as it bends over the "longer length" in accommodation) in the presence of modern caustic boiler treatment or, prospectively, something like Porta-McMahon (now just called "Porta Treatment"). I believe some of the premise is that if the boiler is cycled dry as seldom as possible, and the 'right kind' of scale is arranged, and aggressive deoxygenation is practiced, even if stuff gets preferentially deposited in the 'crevices' they will not proceed to cause SCC or other corrosion-related issues in the gap. I think one of Matt Janssen's photos was intended to illustrate this (in a German boiler). Presumably it is relatively easier to achieve a full-pen join between the face of the fillet and the end of the stay than to do the same in a countersunk recess that only with the greatest of ingenuity will be downhand at working time.

For full-pen bolts: I can't imagine installing these without fairly involved jigs for cutting the correct countersink at relative position in both sheets, and then providing alignment for the stay relative to the countersink as cut. The necessary welding is, or ought to be, assisted by using the end of the stay and the telltale hole in it as a center. You would probably be using some sort of borescope into the waterside to be able to see the appropriate 'fillet' all the way around on both inside welds during the first passes at the closest fit in the countersinks.

In theory, when removing one of these bolts, you'd have a cutter that registers with the telltale hole in the stay, or a drilled-out datum hole corrresponding reasonably to concentricity. It's interesting to think about the different methods that could be used to cut these out with minimum enlargement 'kerf' of the holes in the sheets. In fact if the weld and the staybolt metal are both still good, it would be possible to cut out the 'replacement' countersink for a new full-pen weld as part of the removal of the old bolt, physically continuing the countersink angle into the metal of the bolt and then drilling transversely to the right install diameter -- essentially now bushed with a few 16ths or so of stay metal.

It's a little involved to arrange multiple heat and controlled atmosphere for good laser keyhole fusion welding. But I think this represents one of the better prospective technologies for semi-automating the installation (or, at least, making it a little less idiot-expert-sensitive!) I believe multiple laser heads, or final active optics, can be installed on one 'cutterhead' frame to get the appropriate registration.

Why anyone, any time, would consider structurally welding a threaded stay is entirely beyond my understanding. Aren't these things iron already, not alloy? I won't go into all-thread because no one here would use such a thing, and knows really, really well why.

Seal-welding, as Kelly indicated, is a maintenance procedure, not an option. If you start to see burning or erosion that might compromise the "seal" integrity -- put a little more on, or one of those UP-style flame hat diverters, and grind and pound it out.

I have a fundamental issue with the idea of bushings. These are in double tension when loaded, presumably made at minimum ring thickness so the hole in the sheet can be minimized and the bolt crest/major diameter as large as possible. These seem likely to crack circumferentially between inner and outer roots, invisibly to the point they might catastrophically fail in tension, How thick does a bushing have to be to be threaded ... and wouldn't it be better to treat a bushing, in a correct alloy, as a big, short full-pen welded staybolt with a larger hole up the middle (which is then relieved and tapped with an appropriate staybolt tap for a correctly-proportioned standard staybolt)?

I still have trouble with how those 12 staybolt holes got deformed enough during ordinary fabrication that drill bits broke off in them. Are there not proper side-cutting bits that could restore the telltale bore to relative concentricity and appropriate flow patency, even if deflected by cold stresses?

A point of clarification:

I said that Gary installed a half-dozen tubes to hold the new rear tube sheet in place. I believe those tubes were installed correctly, in the proper holes. The patch at the front tube sheet was not in place yet, so there was not a "starter point" that could have caused the resulting tube misalignment by the subsequent crew. I'm speculating a bit, but do know that unless it was corrected, the patch had a wrong tube pattern.


For those readers not "in the boiler world", staybolts were simple wrought iron for many years. Wrought iron is softer than steel. Steel boiler plates move with the expansion and contraction of the firebox, and the softer wrought iron allowed the bolts to flex better without cracking or breaking. The "fiber" in the wrought iron actually helped this motion. However, as steam pressures were increased, wrought iron gave way to soft steel for staybolts, which is still current practice. The ASME code spec for most staybolt applications is SA675, or more commonly SA36, both of which are weldable with common methods. No alloy.

I only welded bushings in a few times and I wouldn't recommend it. The material in the bushings is usually pretty thin, and some times after welding the inner diameter of the bushing warps enough that a bolt will not go through it. So you have to run a drill or reamer through it. If it warps bad enough the drill may punch through the thin material and rip it apart. Then you have to do it all over again.

There is a thread repair kit called Time Sert which not many people have heard about but gives incredible results. It is similar to a helicoil but uses a special tap, and countersink. You drill out the bad hole, tap it with their tap, insert the bushing, then use a special tool to enlarge the bushing in the hole. After you are done you can grind anything sticking out the hole flush and you will not see any lines from the bushing. It looks like the original hole. It's also water and oil tight. Used that kit hundreds of times and you can repair a hole in just a few minutes. The kits are a bit pricey but worth every dollar. A short video on the subject https://www.youtube.com/watch?v=anjDQJtWFc8

Watched the video and it appears to be a basic "helicoil" type repair. They do work great in a lot of applications. Have never heard of them used in boiler repair? Not saying it isn't so but I am surprised it would be allowed?

The "asshole buttons" or what ever they are called that I saw were not thin or something I would of been concerned about failing when tapped. I think that if one of them failed after or during installation you would have bigger problems contributing to the installation failure? I do love the technology and see many applications for this kind of thread repair on non pressure vessel applications. Not saying this isn't allowed but am surprised and never heard of it being used in staybolt applications. A lot that I have not heard about as I am not a contractor working in the business. But have been involved in repairs over the years.
Regards, John.

The time-sert might work if you can get them in approved material with a MTR that satisfies code requirements. Otherwise they are a bad idea.

.

Kelly,

Can you describe the staybolt hole welding reclamation process you mentioned above in greater detail? Specifically, given the confines of the rather small working area how an effective weld is produced?

Best,
DC

.

It's not difficult. This video gives a understand on how it is done. Only takes a few minutes. As I said before it is unnecessary to completely fill the hole up. Usually once around the hole is enough. https://www.youtube.com/watch?v=ceigKMDJ-qE

As far as using Time Serts for steam locomotives? I don't believe they have inserts past probably a 1" hole. They are water and air tight. I never had one leak and we used them often on EMD and GE locomotive blocks. I do agree that that welding bushings or using bushings is not a good idea. Bushings are good and used often in the hydraulic industry. Sooner or later the hole that the hydraulic ram is connected to will have slop or free play in it. Instead of welding you simply slip a sleeve (bushing) into the worn out hole and you are good to go for another couple years.

Tom,

Thank you for sharing! While I'm not currently a certified pipe welder, I do know my way around electrode selection and welding technique. I have a few questions as a result of watching this video:

1. It would seem to me that the method shown in that video would be one way to guarantee and abundance of slag inclusions. Would a start/stop welding technique still be employed when closing up an oversize staybolt hole? Or would you do this in a continuous pass?

2. I realize he was using a 6013 electrode and your repair method is governed by what procedures you have detailed in your quality manual as an "R" stamp holder. If the SMAW process were to be used, what rod would typically be selected for this?

3. How do you guarantee uniform weld thickness coinciding with the thickness of the sheet as you get closer towards the center of the hole? I was hoping they would show the back side of the closed up hole in the video, but they didn't.

Appreciate the discussion!
DC

Donald the person who posted the video is a bit of a amateur welder from what I have seen complete with the Harbor Freight welder. Normally you would just run one pass completely around it, chip the slag, let it cool for a bit, then run another. He is probably on the brink on slag contamination which cools quickly. If the slag is still red hot it will be vaporized in the arc if restarted and you will be safe. Once it cools and turns black then you can't weld over it with out problems. With Mig welding you can often fill a entire hole like that in one shot if the metal is thick enough. In the case of the locomotive boiler. That metal is very thick. So you could do a single pass easy. However one pass would only cover a area of about 1/4". You would have to do four complete parallel passes if the plate was 1" thick then repeat to close the hole.

Smaller, deeper, holes say less than 1" across, take much more work because the slag has no where to go. In that case you have to weld for maybe a few seconds, stop, chip out all the slag, clean it out really good with compressed air, maybe even run a small carbide bit around the top of the weld with a air grinder, then repeat. It could take you maybe 10 minutes to do that hole.

Most arc welding is done with the 7018 rod. The 6,000 series rods are very small, and takes a long time to get anything welded with it. Since they are small they are much more precise and often used as the root welds in important projects. Farmers love the 6013 rod as it can burn through paint, rust, dirt, etc and still produce a good weld. It's also a good rod if you are in a tight place and can not clean the metal before welding. The 7018 rod is a excellent all around rod and will always give you good results as long as the metal is clean. You can also lay down a lot of metal with it.

Not many industries still use welding rods. Majority use Mig welding which works great but it has it's limitations with amperage and wire size. Big, thick, metal is welded with dual shield welding which is just like Mig welding but leaves slag on the weld like arc welding which must be chipped off. If I was working on boilers dual shield is a good choice and will get things done quickly. However you typically need a stand alone transformer for the high voltages which can run over 200 amps. It's also more dangerous with the huge amount of bright light and U/V radiation so you often have to use the darkest lens.

The uniform thickness of the hole is the tricky part. As you get closer to the center of the hole, at one point, all the molten metal will just close the hole up. Most people stop there. The center will be thin. It takes practice but after the hole closes you stir the molten steel using the arc in circles while pushing the rod slowly into the puddle. All that molten steel is going somewhere and it goes to the other side of the puddle. If you get it too hot the molten puddle will collapse and fall onto the ground producing a huge display of sparks. So you want to push as much metal as you can into the puddle and stop just as it starts to sink. If you did it right you will have a nice button of solid steel on the other side sometimes nearly smooth and flush. My co workers would see the underside of my weld and say "how did he do that"? I always ran a couple of parallel straight welds over the top of the hole just to make everything uniform then ground them off.

If you a filling a hole where you can not see the other side or have access to it, then you should first measure the depth of the hole. If the hole is on the bottom then it's easy. You can pour in the weld and heat and the molten puddle will by gravity, naturally move and collect around the bottom of the hole. You make a single pass around the hole then measure the depth from the lowest part of the weld. Typically you will have a 1/4" weld which means the weld is at least 1/4" into the other side of the hole. If the hole is in a wall or overhead you will be fighting gravity. In those cases you may need to spot weld as shown in the video to keep the molten puddle from moving during the first pass.

When I was working in the shipyards we used a very neat welding technique that I have not seen used anywhere else. When welding floors we had a 1/4 gap between the plates. They gave us these long rolls of white ceramic tiles with a groove down the middle. The tiles were 1" X 1" and glued to some cloth. You could rip off a piece as long as you wanted and the tiles could bend in any direction. Before welding I would go to the underside of the floor and tape these tiles so the grove was under the 1/4 gap. We used metal tape to hold up the tiles from the heat. When I was welding from above I would weave that molten steel back and forth between the plates and the molten steel would fall into the groove of the tiles. When I was finished I would rip of the strip of tiles and you would have a perfect weld on the underside. Was a really amazing process not to mention time saving. Not sure if they could fit the tiles it into boilers but it would be worth looking into.

You've got to center a fillet welded bolt to avoid deformation and a full pen bolt for root penetration - A number of people have their own recipe for a fixture. It is advantageous to avoid a tack weld, or at least one that is not fully consumed in the weld, as that material is going to become very stressed. It can be as simple as a non-ferrous sleeve with a window in the side to start your weld.

As for welding-up holes, you need to get rid of the threads and any nasty stuff and then it is pretty easy to run around the inside of the hole with 5P E6010 starting from the waterside. 1/8" is usually fine, but you can go to 3/32" which will fit in about anywhere.

Make yourself a 4 bolt mock-up of two sheets and try out different styles on the welding bench and most of your questions will be answered - especially if you remove them when you are done. Gary Bensman taught me how to cut threaded bolts out with an oxy-acetelyne rig with no nicks on the hole threads and that is particularly satisfying when you get it right.