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)

 

[ehbadger]

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.

 

[byrdj]

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?

 

[ehbadger]

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.

 

[itsmoked]

Man those are just nasty!!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Artisi]

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.)

 

[ehbadger]

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.

 

[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?

 

[LittleInch]

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.

 

[MJCronin]

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-bolts.html

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

 

[ehbadger]

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 so we ended up torching it out today.

 

[ehbadger]

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.

 

[A8yssUK]

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

 

[ehbadger]

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.

 

[Compositepro]

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

 

[boo1]

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.