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Help me get these studs out
7

Help me get these studs out

Help me get these studs out

(OP)
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)





RE: Help me get these studs out

Get a heavy sledge and beat them down to break the the rust loose. At that point you can get them to turn the the rest is easy. I just hope that you backed those nuts off a couple turns before welding them all.

RE: Help me get these studs out

many decades past, I had a similair problem, but MUCH bigger studs/flange.
We used a "hole saw" that cut between the stud and flange.

RE: Help me get these studs out

(OP)
Screwman1:
We did not back them off (welded while process online so we couldn't loosen them). However as we are shut down now we can re weld them with the nuts backed off since the first welds sheared off anyway.
We prefer not to sledge; as the vessel is brick lined. We did attempt this a bit yesterday with a 4ft sledge and got one to break loose, still takes quite a beating. The other thought was back the nuts off about halfway then seat a jackhammer bit inside and just pound away, but again, not ideal with the brick lining.

RE: Help me get these studs out

(OP)
byrdj:
That sounds awful, but effective. Probably a good last resort.

Right now we are having some success with a 1/2" shear pin drilled through the side of the nut. It is just slow going.

RE: Help me get these studs out

Well, I would not have welded all the studs, yet.

If they're really, truly, anomalously stuck...and you have a bunch of them to remove...building a tool could be prudent.

I might try a hydraulic pulling cylinder with a threaded rod end mated to the stud with a coupling nut. Use a section of heavy wall tubing for a standoff, to bear on the flange. Cut a window in the tubing so you can hit the coupling/stud with a big air chipping hammer. Pull HARD, then continuously apply the hammer.

Take significant precaution to guard against the apparatus launching upward when the stud breaks free, or simply breaks.

This is only my opinion, NOT based on experience!

RE: Help me get these studs out

It is hard to see if the stud body is smooth, or fully threaded.

Regardless, I'd heat the stud to a cheery (maybe even cherry) red glow for a while, so the stud body surrounded by flanges got glowing hot too. Then I'd let it cool off a bit, expecting the corrosion in the gap would have been crushed and broken by the hot swollen stud. In addition, the red hot stud body might "upset" a little and upon cooling be smaller than before.

The theory of heating the nut, hoping to make it expand and be looser and loosenable has not tested well.
For me, loosening more traditionally sized rust seized fasteners by aggressively heating the bolt/stud has been 10X more effective than heating the nut ever was.

RE: Help me get these studs out

Given the corrosive conditions and the experience with the frozen studs:


1) What should have been a much better flange/fastener design ? (I am thinking longer studs and double nuts on top)

2) What fastener materials/coatings should have been used ?

3) Am I correct to understand that there was widespread flange leakage of a corrosive liquid that caused the problem ?

4) Is there a reason that the traditional removal solution mentioned above( lots of heat) can't be used here ?

5) PTFE coatings have temperature limits. What is the operating temperature of the unit ?

MJCronin
Sr. Process Engineer

RE: Help me get these studs out

Who knows what I would have done, but from my comfy sofa, I'd look at getting a rig that does bolt tensioning on structural bolts and using that on the ends of the studs. The math tells me that a good pull will stretch the stud a bit and that the diameter has to decrease. That should lower the compression between the stud and the holes that the corrosion products have built up to allow one's choice of penetrating lubricant to slip in while also shearing the corrosion.

https://www.youtube.com/watch?v=ef9CXDhzH-U

In your case, remove the nuts so there is access to apply penetrating oil to lube up the corrosion products. Work around the flange from stud to stud until they are free. It may take a few passes. The bolt tensioners are daisy-chainable so the entire flange has a uniform pre-load. It may be worthwhile to do the same to remove these studs rather than just one at a time.

A feature to note is the studs -were- stretched by the nuts and are now both shorter and larger in diameter than when the corrosion formed, so the friction in there goes up when the nuts are loosened.

RE: Help me get these studs out

expanding on 3DDaves comments. I have used hollow cylinder rams, with a pipe sheeve around the stud and a piece of thread rod attached to the end of the stud. In my case the stud's were centered drilled and end tapped. thread rod could be welded to the end. a blast shield is needed in case (when) the rod snaps prior to pulling the stud

RE: Help me get these studs out

Have you considered drilling into each stud with the thread tapping size drill after the necessary smaller pilot hole/s, followed with appropriate tap. A major undertaking but it would seem you have a big job ahead of what ever path you take.

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.)

RE: Help me get these studs out

Hard to position the necessary drilling tool under the pipelines that connect to this flange at 90 degree elbows. Unless that part of the pipeline can also be removed. They say that drilling 3/8" holes has been difficult, so I expect drilling 1" holes will be proportionately more difficult. The bit will want to wander off the axis of the studs, cutting into the lower flange's holes. They probably don't want to risk damaging the boiler or its flange.

STF

RE: Help me get these studs out

Assuming you can access the studs, cut the studs off flush at the top of the flange, carefully centre punch the stud, drill a small hole initially and increase the drill size in a couple of steps. This is not a job for your average boiler-maker / welder, you need a fitter or machinist with experience. Correctly done there is little chance of the drill running off axis.

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.)

RE: Help me get these studs out

(OP)
Thanks for all the help; sorry on the delayed responses but I will try to answer everyone in order:

Quote (Nescius)

If they're really, truly, anomalously stuck...and you have a bunch of them to remove...building a tool could be prudent.

I might try a hydraulic pulling cylinder with a threaded rod end mated to the stud with a coupling nut. Use a section of heavy wall tubing for a standoff, to bear on the flange. Cut a window in the tubing so you can hit the coupling/stud with a big air chipping hammer. Pull HARD, then continuously apply the hammer.

Building a tool is definitely on my list. We already have a custom "wrench" of sorts to fit down through the gap in the grating and curls underneath the vessel flange to hold that bottom nut.

That coupling nut sounds interesting; to be clear, is this an extra nut threaded onto the top of the stud? Interesting idea, I will note it down.

Quote (Tmoose)

It is hard to see if the stud body is smooth, or fully threaded.

Regardless, I'd heat the stud to a cheery (maybe even cherry) red glow for a while, so the stud body surrounded by flanges got glowing hot too. Then I'd let it cool off a bit, expecting the corrosion in the gap would have been crushed and broken by the hot swollen stud. In addition, the red hot stud body might "upset" a little and upon cooling be smaller than before.

Stud is currently fully threaded.
I'm not sure heating the stud is an option. Due to the brick lining, the flange insert and brick acid membrane is susceptible to damage at temps >250F. I think heating the studs that hot, even one at a time, would ruin the membrane at the bolt holes.

Quote (MJCronin)

1) What should have been a much better flange/fastener design ? (I am thinking longer studs and double nuts on top)

2) What fastener materials/coatings should have been used ?

3) Am I correct to understand that there was widespread flange leakage of a corrosive liquid that caused the problem ?

4) Is there a reason that the traditional removal solution mentioned above( lots of heat) can't be used here ?

5) PTFE coatings have temperature limits. What is the operating temperature of the unit ?

1. Not sure. Vessels were built in the 60s I think, so short of unbricking 4 layers, cutting out the existing nozzles and extending them, I think we are stuck. Plus all the piping on top would need reworked (not cheap; most is tantalum).

2. Cannot use SS fasteners due to SCC risks. So studs are B7 carbon steel. We are going back this time with PTFE coated bolting. Probably still not the best all things considered but it's all we can do in our short turnaround (this time)

3. Not really leakage at the flange. Reactor have hot HCl (think >140C) and we don't really detect anything, but permeation or some other mechanism we definitely get corrosion.

4. See previous response to Tmosse; in short, vessel is brick lined and cherry red studs would ash the pyroflex membrane requiring a nozzle rebrick.

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

RE: Help me get these studs out

(OP)

Quote (3DDave)

Who knows what I would have done, but from my comfy sofa, I'd look at getting a rig that does bolt tensioning on structural bolts and using that on the ends of the studs. The math tells me that a good pull will stretch the stud a bit and that the diameter has to decrease. That should lower the compression between the stud and the holes that the corrosion products have built up to allow one's choice of penetrating lubricant to slip in while also shearing the corrosion.

https://www.youtube.com/watch?v=ef9CXDhzH-U

In your case, remove the nuts so there is access to apply penetrating oil to lube up the corrosion products. Work around the flange from stud to stud until they are free. It may take a few passes. The bolt tensioners are daisy-chainable so the entire flange has a uniform pre-load. It may be worthwhile to do the same to remove these studs rather than just one at a time.

A feature to note is the studs -were- stretched by the nuts and are now both shorter and larger in diameter than when the corrosion formed, so the friction in there goes up when the nuts are loosened.

Good thought. We are a bit crunched for time right now - I will have to look into the time component of stretching each bolt. I think the time can be scheduled around (in the future). It is just hard now to know whether we can get these covers off in 1 day or 6. If it is reliably say 4 days, yeah it is a long time but at least consistent and can be planned for.

To your last point, that is definitely true. Kind of a catch-22; to remove the stud you need to remove a nut, but by removing a nut the stud gets stuck more.


Quote (byrdj)

expanding on 3DDaves comments. I have used hollow cylinder rams, with a pipe sheeve around the stud and a piece of thread rod attached to the end of the stud. In my case the stud's were centered drilled and end tapped. thread rod could be welded to the end. a blast shield is needed in case (when) the rod snaps prior to pulling the stud

Make sure I get this right; you drill and tap directly into the top face of the stud and thread in another rod, one end of which is connect to the ram? Sounds like it would work. Still requires a lot of drilling though. Hmm

Quote (Artisi)

Have you considered drilling into each stud with the thread tapping size drill after the necessary smaller pilot hole/s, followed with appropriate tap. A major undertaking but it would seem you have a big job ahead of what ever path you take.

I am not sure what you are going for here.

Quote (SparWeb)

Hard to position the necessary drilling tool under the pipelines that connect to this flange at 90 degree elbows. Unless that part of the pipeline can also be removed. They say that drilling 3/8" holes has been difficult, so I expect drilling 1" holes will be proportionately more difficult. The bit will want to wander off the axis of the studs, cutting into the lower flange's holes. They probably don't want to risk damaging the boiler or its flange.

Definitely don't want to damage the lower vessel flange.

RE: Help me get these studs out

(OP)
Thanks all for the responses. Definitely some things/ideas to consider. In summary, and not to rain on any ideas but just to clarify some constraints:

1. Right now anything with drilling is not ideal as it takes a long time.

2. Heat is not ideal. The vessel flanges have an acid membrane that gets ruined around 250F.

3. Excessive pounding is also not ideal as the brick inside can fracture off.

4. Access to the lower side of the flange is minimal due to vessel construction.

In the future, I imagine I may have to concede in some fashion on one or more of these points. Whatever solution developed may be able take some time as long as it is consistent, as that can be planned for. Nowadays we never know if this job will take 1 day or 5+. I like the idea of a hydraulic ram type solution if we can figure a way to make it work without requiring a lot of drilling or helped along by pounding.

I'm also considering bolting MOC change to something less susceptible to corrosion if the PTFE coating doesn't work. However, any alloys would definitely be costly. I've got 18 of these flanges on site purpleface

Again, thanks all for the input so far. Much appreciated!

RE: Help me get these studs out

You may consider the liberal use of polysulphide rubber to exclude the ability for corrosive materials to enter the threads in the holes in the first place. It will protect the surface of the fastener and the hole. If you use hydraulic tensioning on the studs on the flanges then you can apply it to the portion that is in the nut threads without affecting the torque levels, which you will no longer use/depend on.

RE: Help me get these studs out

If beating it with a 16 pounder eventually loosens it, is there any possibility that sustained use of a large electric breaker would vibrate it loose? Something like https://www.hilti.co.uk/drilling-and-demolition/de... with an adaptor perhaps. Not sure if that would also damage your brick lining.

RE: Help me get these studs out

Have you thought about a cutting torch? In my experience, the burn usually is usually interrupted as you go from one piece to the next. You could burn through each nut from top to bottom and that would relieve the tension. Top to bottom on both sides and it should just split off. The boundary provided by the washer should protect the flange. If you start your cut at the top and burn down, you will minimize heat transfer to the flang. Ice or wet rags will keep the area from heating as well.

RE: Help me get these studs out

Many times I've had "Liquid Wrench" work when all hope was lost. Have you tried anything like that?

Keith Cress
kcress - http://www.flaminsystems.com

RE: Help me get these studs out

The photos show several cans of what I think is Kroil, the gold standard for thread loosening liquid products.

Mike Halloran
Pembroke Pines, FL, USA

RE: Help me get these studs out

(OP)

Quote (moon161)

Have you thought about a cutting torch? In my experience, the burn usually is usually interrupted as you go from one piece to the next. You could burn through each nut from top to bottom and that would relieve the tension. Top to bottom on both sides and it should just split off. The boundary provided by the washer should protect the flange. If you start your cut at the top and burn down, you will minimize heat transfer to the flang. Ice or wet rags will keep the area from heating as well.

Problem is not getting the nuts off, it is getting the stud out.

Quote (MikeHalloran)

The photos show several cans of what I think is Kroil, the gold standard for thread loosening liquid products.

Yeah I think we've killed a couple cases of Kroil so far.

RE: Help me get these studs out

(OP)

Quote (3DDave)

You may consider the liberal use of polysulphide rubber to exclude the ability for corrosive materials to enter the threads in the holes in the first place. It will protect the surface of the fastener and the hole. If you use hydraulic tensioning on the studs on the flanges then you can apply it to the portion that is in the nut threads without affecting the torque levels, which you will no longer use/depend on.

A quick google indicates this rubber is not suitable for HCl exposure (main corrosive agent here). Last paragraph here:
http://www.efunda.com/glossary/design/oring/design...
I'll keep looking though, that source seems a little sparse though.

RE: Help me get these studs out

The stud to flange freeze is the focal issue here. The stud needs to turn in the flange. Can you grab your top welded nut and the bottom nut at the same time with, say, box wrenches and turn them both at the same time in the same direction. I'd probably try using 8 to 10 foot cheaters on the wrenches or impact sockets and breaker bars.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Help me get these studs out

Nescius first suggested (but I missed his post)

my second post was related to experanice with fitted coupling studs. In my case, the studs are through drilled originally.

In your case, posibly use a coupling nut to extend a stud up through a standoff, then through a hollow ram, with a nut/washer to pull from.



Have you contacted an EDM stud removal service?

RE: Help me get these studs out

ehbadger: to clarify my suggestion; assuming you can access the studs and centre drill the stud with a small pilot drill followed up with maybe 1 or 2 intermediate sizes and finally with the appropriate thread tapping size drill, once done you can "re-tap" the flange which will remove the remnants of the stud.
This technique is nothing new - been there and done it myself.

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.)

RE: Help me get these studs out

Well, technically, you have three different problems. All with the studs, nuts, and cover plate, but three different problems.

You have to remove the cover plate, then LATER put it back on and re-torque it.
To get the cover plate off for the other work, you only need the nuts (now destructively) removed, but the studs do not need to come off nor be pristine and clean to remove the cover plate. So you can burn through the studs as well, or weld a upper nut to the current nut and torque on both. Or burn through the outside of the nut to cut it in half across the stud. Then break off the two halves.

You have to remove/destroy the nuts, but since you are willing to destroy the studs to get the nuts off, you don't need to be gentle about removing the nuts right now. however, the more studs you salvage, the fewer you have to drill out and replace with new studs when it comes time to replace the cover and re-torque it down.

in removing stuck nuts/studs from turbines, we seldom see the sledge hammer work when just hitting the nuts from the side. it might, but usually they cut the studs off just above the split lines or the valve covers. If there are only 2-4 threads left of the cut-off nut, that little bit can be hand-ground off or broken off.

Certainly try to unscrew as many as possible, but don't "not drill" because two nuts are under the supply pipe. It will have to come off anyway because the cover has to come off.

Don't be too wuick to drill out to the tap drill size, stop 1/64, may 2/64 smaller than the tap drill diameter since it is very difficult to exactly center the new drilled hole. try to kiss the internal threads of the holes on one side of the hole, then the remnants of the studs can be picked out with a dental prick fairly quickly.

If the nuts are burned off, the cover can be pulled off from the remnants of the studs. Then the internal work can proceed while you drill out the studs and re-tap the holes and replace the studs.

RE: Help me get these studs out


Did we hear if the studs are full threaded, or have smooth ~ 1.75 inch DIA bodies?

You say you can always get the nuts to break free.
Maybe you said you tried this already. If so, I missed it. Sorry.

step 1 - remove the lower nut. Contemplate re-installing it 3 turns to prevent the stud from becoming a projectile during step 5..
step 2 - remove the upper nut, then wire brush clean the stud's upper threads.
step 2A - If the studs are not fully threaded, note how many threads (and thus turns of the nut) are possible before jamming the nut on the stud threads
step 3 - apply Kroil, etc
step 4 - slather the flange, a grade 8 flat washer, and the stud threads with ARP ultra torque lube
step 5 - install the grade 8 washer and a new nut on the prepared stud and tighten the beejesus out of the new nut to make the stud it's own puller. Add washers to keep the nut from bottoming on the stud thread if the stud fights every inch of the way.

If the above procedure is not 100% successful, or too difficult, I'd still look into pre-heating the stud as high as possible to crack the corrosion, no matter what extraction method is used. Maybe heat the stud while shielding the flange from flame, and stopping when the flange is hot enough to make water evaporate but not sizzle.

A chemist might know what nasty solvent aggressively attacks your specific corrosion products.

The bimetal or carbide or grit hole saw sounds intriguing.
http://www.steel-flange.com/ASME-B16.47-SeriesA-MS...,
There should be about 0.06" radial clearance around each stud, even if unevenly distributed.
A thin walled shell saw could be made out of fairly ordinary steel, since it would only have to cut crusty corrosion, not steel flanges or fancy bolts.

I'd make a fixture to provide a steel surface for a magnetic base drill, and faciliate automatically drilling the studs on center. It would reference off the stud OD, and be secured with nuts on a couple of adjacent studs.
It would help on many of the 28 bolts that appear to have an unobstructed straight shot.

RE: Help me get these studs out

Maybe use a riveting gun to hammer the studs. Not as hard hitting as a breaker and with a higher frequency. Rattle the corrosion loose.

Ted

RE: Help me get these studs out

2
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.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Help me get these studs out

(OP)
Thanks again all. This gotten a lot more attention that I expected... but I suppose most engineers are inherent problem solvers and this is a "fun" one to think through.

Tmoose:
Yes I think I mentioned it before, but the studs are fully threaded. The flange holes are not threaded; they are just 300# flanges (B16.47 Series A Class 300)

I think I actually mis-spoke in my OP (can't seem to edit it either, hmmmm), and I realize this affects some of the solutions mentioned (sorry! - I should've caught this sooner) but we cannot move or remove the bottom nut while the stud is still frozen. Since we do not have wrench access to the underside of the flange, and with the stud frozen to the flanges the only way to loosen the bottom nut is by turning the stud. My second photo, in the 5 o'clock position, you can see the tool we use to hold the bottom nut from the top (this works when the top nut is fixed to the stud and both are turned like a bolt).

RE: Help me get these studs out


ehbadger (Chemical)(OP)19 Sep 16 11:11 wrote:
"This gotten a lot more attention that I expected... but I suppose most engineers are inherent problem solvers and this is a "fun" one to think through"

the reason could be we have worked outages and KNOW that if your project unexpectly becomes the critical path, management then "helps" by forcing more supervising personnel over you.

RE: Help me get these studs out

You could try and use a bottle jack to press the studs out. You could hold it down using the adjacent studs.

RE: Help me get these studs out

(OP)

Quote (moon161)

You could try and use a bottle jack to press the studs out. You could hold it down using the adjacent studs.

There is not enough room to press them out towards the bottom. Or am I misunderstanding your suggestion? Although maybe could potentially press it down enough to break it loose, maybe 1/2", then pull it back up.

RE: Help me get these studs out

"...cannot move or remove the bottom nut while the stud is still frozen."

Nasty. How much vertical clearance is there under the bottom nut? Enough room for a torque multiplier? (I doesn't look like it. sad)

If some of the suggested methods for pulling the studs out from the top seem worth trying, it might be worth it to invent a clever way to remove the bottom nuts first...or at least back them off a couple of turns to allow pulling from the top.

RE: Help me get these studs out

Well, I warn you, the attached sketch is of the "5-minutes-on-a-napkin" variety. It's a way to improve the performance of offset wrenches, if that's all that can access the bottom nuts.

It'll still be a "big ask" for the wrench, so build it as big as will fit, out of strong stuff. In the end, though, sometimes even a 10 or 15 foot cheater bar just doesn't have the mojo of an impact wrench.

Edited to add: If you have the room to build the wrench nice and big (stiff), you might try using it as a striking wrench instead of using a cheater. Be careful in either case.

RE: Help me get these studs out

Pull the top nuts, make a custom C clamp to push the studs down with lower nuts still on them? Bottom end would be forked so you can straddle the nuts. If it works, it will probably shoot the studs down with a good amount of force, so plan to address that somehow.

I'm talking a monster custom clamp, start with a solid block of steel, mill out the middle (big radius on corners) then drill/tap one end, mill a slot in the other to straddle the nuts, make the top/bottom as thick as will fit.

I could sketch it but I think you get the idea. Hold your fingers and thumb like you are about to use a syringe, that's how the clamp would function.

RE: Help me get these studs out

Quote (itsmoked)

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.

Best idea so far, in my opinion.

RE: Help me get these studs out

" Although maybe could potentially press it down enough to break it loose.... "

Yes, I'm guessing, and expecting, once you get the stud to slide downward the rest of the removal process will be relatively easy.

RE: Help me get these studs out

I was looking for a diamond wire saw but found this. http://miragemachines.com/products/pipe-casing-cut...
if there is enough space to drop the half stud and nut then I would investigate stud bolt cutters

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

RE: Help me get these studs out

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

RE: Help me get these studs out

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: Help me get these studs out

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.

RE: Help me get these studs out

(OP)
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 :)

Quote (itsmoked )

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.

Quote (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.


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.

Quote (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.

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.




RE: Help me get these studs out

(OP)

Quote (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

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)

RE: Help me get these studs out

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.

RE: Help me get these studs out

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

RE: Help me get these studs out

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.)

RE: Help me get these studs out

(OP)

Quote (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.

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.



RE: Help me get these studs out

"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.

RE: Help me get these studs out

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.)

RE: Help me get these studs out

(OP)
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 surprise so it might be another day or two.

EDIT: Got some photos

This is one we removed:


This is what is going back in:

RE: Help me get these studs out

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

RE: Help me get these studs out

(OP)
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.

RE: Help me get these studs out

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

RE: Help me get these studs out

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.

RE: Help me get these studs out

(OP)

Quote (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.

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.

RE: Help me get these studs out

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.)

RE: Help me get these studs out

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.

RE: Help me get these studs out

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.

RE: Help me get these studs out

(OP)
Been a few days so a quick update...
Covers are off, but we still have some frozen studs stuck in. A 20lb sledge hammer wielded by a mechanic self-proclaimed as "Thor" couldn't not get them to budge. They've been soaked in aerokroil constantly for a couple days now.

Going back, the holes will be cleaned out and the new PTFE coated bolting will be antiseized.

We had some "fun" with the RAD gun, here is what 8,000 ft-lbs will do to a 1-3/4 stud with the nut welded on




Here is inside one hole after stud removed (different flange but same vessel as above pics). This stud came out relatively easy compared to the ones pictured above.




RE: Help me get these studs out

WOW. Good to hear cover is off.

looking at the holes, I'll ask if you are set up to power ream the holes clean?

RE: Help me get these studs out

(OP)
byrdj

We are currently using a flapper wheel with a drill to clean out the holes. They just started on that this morning and from what I've seen so far it seems to be working well.

RE: Help me get these studs out

Why so corroded, leaky flange gaskets?

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.)

RE: Help me get these studs out

(OP)
I'm not entirely sure. For these problematic ones;
1. I don't know the last time they were apart. I've been in this particular process 4 years and this is my first time seeing them off, so at least that long. Probably much longer.
2. Not sure if the gasket is leaking or not. Although it seems like it might be. We have ambient air alarms, do sniff tests on rounds, etc. So if it is "leaking" it would have to be a very, very slow "leak".

We got all but 1 stud out last week using a (large) jackhammer. Will be attempting to drill it out today.

RE: Help me get these studs out

with the corrosion, the possible distortion and damage from the stud removal, are you going to have the flange faces machined?

what type of gasket and flange profile?

RE: Help me get these studs out

I'm beginning to think you need CRA bolts ( Duplex or stainless). That PE coating won't stand much abrasion if you're turning it in the hole or any leakage from the gasket, no matter how small.

If you can't get them now for the shutdown, do it as hot bolting exercise one by one later on.

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

RE: Help me get these studs out

I agree with LI .....

PTFE will not stand much abrasion, and considering the extreme expense and severe abuse the existing fasteners endured, CRA boltsw should be considered.

Perhaps custom CRA stud bolts with a smooth center section could be used ????

http://www.sigmafasteners.com/duplex-stainless-bol...

I am not 100% sold on duplex stainless materials .... There are other, even more corrosion resistant alloys available, for about the same money ...

Please keep us informed about your progress and final solutions .....


MJCronin
Sr. Process Engineer

RE: Help me get these studs out

(OP)
Not much time for a full response re:stainless bolting but there is definitely a large aversion to stainless steel fasteners in this facility. Chloride SCC is a large issue we fight and have been moving away from any stainless fasteners for a few years now.

That said there is probably some benefit to exploring a CRA bolting solution rather than PTFE coated. It will be interesting to see how it holds up.. everywhere else we used it it's worked very well (but that could also be we took it apart after 2 years rather than 5+). I'm not sure how long this bolting will be in place... shutdowns are typically 2-3 years apart so I imagine at least that long. And probably much longer, unless it's decided to proactively replace the bolting every shutdown.


Also, got the last stud out finally. Drilling it failed as the contract mechanic started the first hole off center banghead so we ended up torching it out today.

RE: Help me get these studs out

(OP)

Quote (byrdj)

with the corrosion, the possible distortion and damage from the stud removal, are you going to have the flange faces machined?

what type of gasket and flange profile?

Being 30" 300# flanges they are quite beefy (4" thick) so I don't think they are distorted any appreciable amount. Since it is brick lined it's not a standard gasket area or anything, it's actually a very wide (maybe 6-8") sealing area. And due to that and how it is constructed there isn't really anything to machine, other than around the bolt holes themselves, which wouldn't help anything but aesthetics... I'd post a pic or detail more but IP and all that... Basically I am not concerned with any of that, we did not affect anything in that respect.

RE: Help me get these studs out

Hello again :) First just want to say this thread is great, being stuck in my gasket R&D lab most of the time its great to see some real world plant problems. So thank you for sharing!

Next on to my area gasketing as it came up, I would also guess this excess corrosion was caused by a permeating gasket, Cl is a nasty ion for permeation.
Now you mention a large flange face sealing area, this could be the issue oddly enough. The large flange area cuts down the amount of gasket stress you can achieve on the gasket (note stress not force/bolt torque). A higher stress makes the gasket more dense aiding more against permeation than width. Everything permeates, it's just a matter of time, increasing the density will decrease the permeation amount, while increasing the width of the gasket will just increase the amount of time it takes to start permeating out and will not reduce the rate.

As you have HCl I reckon you already use PTFE. I would however actually suggest not using the whole flange face area, perhaps use a tape (its width determined by your process max pressure but around 1") placed in a snaking pattern around the sealing area, you'll get a more densified gasket material (due to a lower amount of area being compressed) so lower leakage rate/permeation rates (Using the snaking pattern will reduce flange rotation issues). Or use a gasket with a permeation barrier/film (ala Gore UPG) but these are only made in standard sizes so could be expensive to get customised to your dimensions.

But talk with the engineering department of a quality gasket manufacturer (Gore, Garlock, Flexitallic, Teadit) they should be able to help you with this. Short term pain for long term gain :)

Dan

RE: Help me get these studs out

(OP)

Quote (A8yssUK)

As you have HCl I reckon you already use PTFE. I would however actually suggest not using the whole flange face area, perhaps use a tape (its width determined by your process max pressure but around 1") placed in a snaking pattern around the sealing area, you'll get a more densified gasket material (due to a lower amount of area being compressed) so lower leakage rate/permeation rates (Using the snaking pattern will reduce flange rotation issues). Or use a gasket with a permeation barrier/film (ala Gore UPG) but these are only made in standard sizes so could be expensive to get customised to your dimensions.

Current gasket is actually a homogeneous graphite.

RE: Help me get these studs out

Graphite, steel, and HCl make a pretty good battery.

RE: Help me get these studs out

like you removed the threads from the flange area.
Consider some sealant under the bolt heads to prevent fluids from filling up the area between the shank and the flange.

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