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)

 

[MikeHalloran]

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

 

[ehbadger]

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.

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.

 

[ehbadger]

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--oring--chemical--hydrochloric_acid.cfm

I'll keep looking though, that source seems a little sparse though.

 

[itsmoked]

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

 

[byrdj]

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?

 

[Artisi]

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.)

 

[racookpe1978]

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.

 

[Tmoose]

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-MSS-SP-44-Flanges-Class-300lbs.pdf,

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.

 

[hydtools]

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

 

[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.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ehbadger]

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).

 

[byrdj]

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.

 

[moon161]

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

 

[ehbadger]

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.

 

[Nescius]

"...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. )

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.

 

[Nescius]

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.

 

[1gibson]

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.

 

[SwinnyGG]

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.

 

[Tmoose]

" 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.

 

[LittleInch]

I was looking for a diamond wire saw but found this.

http://miragemachines.com/products/pipe-casing-cutting/bolt-cutting/

if there is enough space to drop the half stud and nut then I would investigate stud bolt cutters

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