Help me get these studs out 7

[ehbadger]

I have some reactors in a corrosive service. Heads are 30" 300# flanges. They were installed with studs. See attached photos

The corrosion between the stud shaft and flange itself locks it up tighter than whatever you can think of that is really damn tight. We can get both nuts to break free but that is actually not helpful as the stud is still "frozen" in place. Also note, the only way to get the stud out is to remove the bottom nut and pull the stud out from the top. We cannot go down because there is no clearance between the flange and vessel itself. Cutting isn't very useful either.

We tried to weld the top nuts to the studs to create what is effectively a bolt. Tack welds at first (didn't work) so we went back around and did the whole circumference. However we are actually shearing the welds with the big torque gun and still not breaking the stud loose. We've tried a ~3/8" interference pin in a hole drilled half and half into stud and nut, which worked for a few, but that is rolling over and not working in most. We tried a hole and pin though the side of the nut into the shaft (shear pin style) but that is shearing as well.
We've got 32 bolts per flange, 3 on each vessel. Drilling 3/8"+ holes for pins/keys is very time consuming and kills a serious amount of drill bits.

Next plan of attack is some hot welding and trying to burn down between nuts and stud and get more area fused. This is also pretty undesireable (but not impossible) due to it being some serious hot work in the middle of a turnaround.

Any creative ideas out there?



Note: For reassembly I am using PTFE coated BOLTS. (not the crappy ptfe coated ones either)

 

[SnTMan]

Having read the foregoing: It seems that a) a fairly small axial movement should break the corrosion products between the stud and bolt hole and b) anything involving drilling is too time-consuming and difficult. I therefore favor a scheme similar to those offered by Tmmoose and moon161.

Given that hammering, etc is out, then I'd say:

1) Back off the top nuts one-two turns
2) Soak the be-jeesus out of the studs with a penetrant and maybe a little heat
3) Press the studs down with a hydraulic cylinder or bottle jack (and suitable restraint fixtures) to break the corrosion
4) Fit the existing back-up wrench, and remove the studs normally

Be easier maybe if all the welding hadn't happened, but too late for that.

BTW I find it odd that the honkin' big impact gun is not threat to the brickwork (maybe it is), but air hammers etc, are out. Otherwise I'd say hammer the studs axially, rather than press 'em.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Compositepro]

My two cents: Penetrating oil takes time to penetrate and trying heat before the oil has penetrated is worse than using no penetrant because you just add carbon deposits to the corrosion. Also, bidirectional vibration is far more effective than blows in just one direction. Often I have gotten a nut to turn slightly and continued turning will just jam the corrosion in the nut tighter until the hex rounds-off or something else breaks. Reversing the blows on the nut (loosen-tighten) frequently is far more effective, even if the nut is already tight. The key is to get the solid corrosion products in the threads to break down into a fluidized powder, preferrably suspended in oil. If you continue to compress a powder that is already compacted it will just jam tighter.

If your problem is getting the threaded stud out of an unthreaded hole, then get a powerful vibrator that can vibrate the stud axially and screw it onto the stud. It is sometimes amazing how much more effective a few thousand up/down blows of smaller magnitude can be than a dozen larger impacts in one direction.
You could make a slide hammer from some all-thread and a coupling nut on the stud.

I do not understand how you can get the bottom nuts loose without turning the studs.

Experienced mechanics/pipefitters are usually much better at solving this kind of problem than engineers.

 

[MintJulep]

If you can't use heat, how about cold?

Fabricate a cup out of Vespel or other cryogenic-suitable plastic and thread it down in place of the nut. Fill with liquid nitrogen.

By the way, you've stated conflicting information about the temperature limits.

5. Operates just under 150C (about 300F). PTFE is OK here.

The vessel flanges have an acid membrane that gets ruined around 250F.

 

[ehbadger]

Again thanks for all the input. I am trying to respond to everyone but if I miss something I apologize. I'm in the middle of a shutdown and this is just one of a dozen jobs I've got on my plate so I appreciate the patience

A carbide sawzall in thru the flange gasket to cut all the studs so you can separate the flanges. Once this is done you can easily roast the studs out of the top flange without worrying about the vessel.

The bottom studs will likely punch out easily since the corrosive agent probably didn't leak all the way down the threads. Also, drifting out the bottom studs should be much easier because only a fraction of the studs are now corroded to flange since you just removed one of them.

If you have to drill, well, with the top flange and pipe removed you'll have a clear area to attack each one and a better plain to attach a magnetic base drill to.

re: cutting - Sawzall/portaband/etc is pretty much out except as a very last resort, as the top covers are tantalum lined on the bottom up to the bolt circle. Too expensive to risk cutting or gouging. However if we CAN cut them in between flanges, yes there is enough clearance below to push them out.
re: drilling - I asked the crew leader about setting up a mag base drill to hasten the effort. He said they though about it earlier but not enough room on the cover to attach, as it is now. We would have to set up a small platform of sorts - not impossible by any means, just something they discounted at first due to the extra effort.

If you can't use heat, how about cold?

Fabricate a cup out of Vespel or other cryogenic-suitable plastic and thread it down in place of the nut. Fill with liquid nitrogen.

By the way, you've stated conflicting information about the temperature limits.

Quote:
5. Operates just under 150C (about 300F). PTFE is OK here.

Quote:
The vessel flanges have an acid membrane that gets ruined around 250F.

Not conflicting. The pyroflex is the layer adjacent to the steel. The 300F is the process temp. There are actually 3 layers of brick internally. It is very close but the bricks insulate enough to keep pyroflex below 250F as required.

My two cents: Penetrating oil takes time to penetrate and trying heat before the oil has penetrated is worse than using no penetrant because you just add carbon deposits to the corrosion. Also, bidirectional vibration is far more effective than blows in just one direction. Often I have gotten a nut to turn slightly and continued turning will just jam the corrosion in the nut tighter until the hex rounds-off or something else breaks. Reversing the blows on the nut (loosen-tighten) frequently is far more effective, even if the nut is already tight. The key is to get the solid corrosion products in the threads to break down into a fluidized powder, preferrably suspended in oil. If you continue to compress a powder that is already compacted it will just jam tighter.

If your problem is getting the threaded stud out of an unthreaded hole, then get a powerful vibrator that can vibrate the stud axially and screw it onto the stud. It is sometimes amazing how much more effective a few thousand up/down blows of smaller magnitude can be than a dozen larger impacts in one direction.
You could make a slide hammer from some all-thread and a coupling nut on the stud.

I do not understand how you can get the bottom nuts loose without turning the studs.

Experienced mechanics/pipefitters are usually much better at solving this kind of problem than engineers.

re: vibration - this sounds promising. How would I look for this? Any keywords to get me started? I wonder if this would cause issues in the brick system at all? Something new to explore, thanks!
re: bottom nuts - See earlier edit... we can't. I misspoke in OP.
re: mechanics - I've been working with a few guys on this job, very good mechanics. Pretty much everything we've tried up until this point has been their doing. I reviewed Nescuis's suggestion with the crew leader today so I think I've planted that seed of an idea for him to think about tonight.

 

[ehbadger]

Having read the foregoing: It seems that a) a fairly small axial movement should break the corrosion products between the stud and bolt hole and b) anything involving drilling is too time-consuming and difficult. I therefore favor a scheme similar to those offered by Tmmoose and moon161.

Given that hammering, etc is out, then I'd say:

1) Back off the top nuts one-two turns
2) Soak the be-jeesus out of the studs with a penetrant and maybe a little heat
3) Press the studs down with a hydraulic cylinder or bottle jack (and suitable restraint fixtures) to break the corrosion
4) Fit the existing back-up wrench, and remove the studs normally

Be easier maybe if all the welding hadn't happened, but too late for that.

BTW I find it odd that the honkin' big impact gun is not threat to the brickwork (maybe it is), but air hammers etc, are out. Otherwise I'd say hammer the studs axially, rather than press 'em.

Regards,

Mike

Mike, I mostly have landed on a similar plan. If we can get the wrench setup that Nescius suggested and get the bottom nuts to break free (for things are welded already) or get the tops nuts loose, then we can use some "force" to drive stud down enough to break it free. "Force" TBD - have many suggestions from this thread to think about... bottle jacks, rams, jackhammers, etc

re: Hammering - I actually spoke with a foreman of the brick laying company (one of these vessels is actually being re-bricked internally right now) and he said hammering is probably not as large of a concern as we thought. So there might be some leeway in terms of jackhammers/sledges after all. Still don't feel super comfortable beating on it with a sledge though.


To answer a perhaps unasked question, the grating issue has been raised in the passed and it gets lots of attention during shutdowns like this and then is one of those things that falls off quickly when it is "out of sight out of mind" so to speak. There is significant structural steel beams very near a lot of these so it is not simple to just pull up the grating temporarily to gain access to the underside of the flanges. I wish it was though! Maybe with all the "pain" this year we can finally justify something (but my PTFE bolts worked very very well in a nearly identical situation last year so hopefully most of this is behind us)

 

[chicopee]

We had a situation where the bolts were frozen to the nuts on a steam line. Time was in favor in our case, so we soaked rags with penetrating oil and wrap these soaked rags around the nuts. Few days later the nuts came free. If you have time and are able to remove the nuts, I would apply the same technique by wrapping soaked rage on the free ends of the bolts and around the heads but for a longer period of time and then punch the bolts out of the flanges.

 

[hydtools]

Look at a hydraulic pin pusher. E.g., WTC
There may or may not be enough access for the c-frame to fit to the underside of the flange. Worth a look. Some are used to remove pins from CAT tracks.

Ted

 

[Artisi]

ehbadger: Please clarify the "stud" terminology you have used, your opening sentence said "stud" -- now having read the complete story I now think you meant the fasteners are thru' bolts NOT studs, which puts a complete different perspective on what I have been suggesting.
The attached is an engineering stud.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[ehbadger]

ehbadger: Please clarify the "stud" terminology you have used, your opening sentence said "stud" -- now having read the complete story I now think you meant the fasteners are thru' bolts NOT studs, which puts a complete different perspective on what I have been suggesting.
The attached is an engineering stud.

Sorry for any confusion. We use the term "stud" here for a fastener that is not a bolt but comprised of a fully threaded rod with two nuts. and perhaps it is not quite correct? It is a fully threaded fastener. The prior PO text calls for:
"BOLT STUD 1-3/4"-8 X 11-1/2" LG B7"

I can grab a pic of a removed one later today, don't have any at my desk this morning.

 

[LittleInch]

"Stud" on its own without "bolt" can be interpreted as being a piece of screwed rod which is itself screwed into a hole, normally into some sort of casting. Often seen on the flanges of pumps and sometimes large block valves made from a single piece of metal.

On occasion it can also be screwed into a tapped hole in a flange, but this is quite unusual.

For me anyway a "stud bolt" is as you've described, i.e. a threaded rod which is threaded the entire length with two (loose) nuts.

Once you've got these mothers off then I would replace them with longer studs so that you can double nut the top nut to give you something to grip on to turn the stud while you hold the bottom nut. You could also use it for tensioning if its long enough.

If you've got any sort of corrosion issue I would not use a headed bolt. They have a tendency to corrode or crack under the bolt head where you can't see an thing. Also if the bolt head shears off then you're not in a good place...

I would still cut the bolts off in between the flanges and be done with it. The diamond wires can be wound and run through pulleys to get to tight locations.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Artisi]

Slight confusion with terminology but now clear.
If all else fails I would give my suggestion re drilling with the tapping size drill and tapping.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[ehbadger]

Well I was going to post some pictures of the ones we had removed so far so you can see the details and corrosion but they were 5S'ed on night shift so it might be another day or two.

EDIT: Got some photos

This is one we removed:

This is what is going back in:

 

[SwinnyGG]

If you don't have access to get the old nuts off, how do you have access to tighten the new ones?

 

[ehbadger]

We can hold the nut with a custom offset wrench we have and tighten the bolt. Since the bolts are 1.75" dia and the holes are 1.875" diameter and there are no alignment issues, we can tighten using the bolt head and hit the expected torque fairly reliably.

 

[djm883]

You may want to coat the new bolt shanks with anti-seize before installing for removal in the future.

 

[natepiercy]

Your second picture in the above post leads me to believe you've got them all out. Is this so?

If not, might I humbly suggest using an abrasive cutoff wheel resting on top of the washer? In my experience, these have less tendency to walk than a sawzall or similar device. If you're concerned about sparks marring your surface, throw a welding jacket over anything you care about.

 

[ehbadger]

Your second picture in the above post leads me to believe you've got them all out. Is this so?

If not, might I humbly suggest using an abrasive cutoff wheel resting on top of the washer? In my experience, these have less tendency to walk than a sawzall or similar device. If you're concerned about sparks marring your surface, throw a welding jacket over anything you care about.

We've got a most of the flanges we wanted to remove off. The ones that were removed our last turnaround came off without too much fuss. I have one and a half flanges still to disassemble. Not sure when the last time they were removed - the "half" we've got so far was last week and is what prompted this post. Fortunately we have some extra time this shutdown to work on it.

 

[Artisi]

Even with your lovely coated blue bolts, I would suggest a good anti-seize is used as the flanges will still corrode and could cause problems further down the track.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[SwinnyGG]

In addition to the anti-seize, I would highly suggest you attempt to avoid turning the bolts in their bores.

In my experience, this is an extremely common cause for fastener corrosion that people over look- turning the bolt in the bore makes it likely that the bore will scratch the coating, reducing its ability to prevent corrosion, or in extreme cases, creating a scratch on the bolt surface that is significant enough to initiate failure during tensioning or in service.

It's certainly possible that you know this already, and in your situation it is impossible to turn the nuts. If that's the case, I apologize for being pedantic.

 

[bigTomHanks]

I had some studs that were similar to the one you pulled out and none of the usual methods were working(impact, heat, welded nut, drilling, penetrating oil, wax, hammering stud,etc). What finally worked was cutting the stud off and use a grinder to get it slightly below the surface. I then used a scribe to dig as much rust out of the top threads as possible and then hit it with some good penetrating oil. After it set for awhile I welded a washer and then nut onto the stud and was able to get them out.