Well, since you can't go by turns because of the knife edge bit, you have to go by elongation or stretch to ensure you have the correct preload.

Stretch is measured by a micrometer. In an industrial application, often times a Go/Not-Go gage is used, this is basically a big machined cast iron horseshoe. It fits around the application. In your case, if the bolt has not yet achieved sufficient preload, then it will be too short. If it's streched too far, it will be too long.

The only concern I would have with this approach is whether or not there is sufficient friction or variability in the "cutting" portion of bolt rotation-- if the material were harder to cut or friction were higher, you might end up with the assembly being longer (because the cutting edge didn't sink in) and give the appearance of correct preload in the fastener when it wasn't actually present.

Indicating fasteners seem to be the right answer . . . they are probably more expensive any may require a redesign.

Can you redesign to use a cutting sleeve of a fixed length that will provide you with a positive stop before bolt deformation begins?

By the way, I am not an engineer. Not by a long shot. If I told you my formal training you would laugh. So don't stand under anything that I advise you on.

...in other words, something like this maybe?

Friction Torque Limiters | Pilot Mount | Mechanisms with Adapters | Mechanisms with Couplings | Flexible Mechanical Couplings | NEMA Frame | C-Face Mount

Perhaps as others have said, a load indicating washer is in order. You can get them that compressor that leak a die, although I suspect that will be forbidden too!

Someone has already calculated that 900ft.lbs will give the right amount of compression, so once you find out what that number is, maybe you can have some load indicating washers made up.

Then you can use your current method for the first four torque amounts (doesnt really matter how bang on they are right?), and then the washer will be used to prove or disprove your final torque.

not sure if you can get load indicating washers that big mind. I've never needed to torque anything that much!!

What diameter are the fasteners?

Do you have room (axial height) for a resonant "torque stick" and an impact wrench?

Torque Sticks, Torque Sockets and Other Discount Tools

Seems to me that torque simply approximates bolt tension. As does bolt stretch. If the bolts are consistently manufactured, then you'd just need to know how much they need to stretch. Once you know this, you can figure the nut revolution that will stretch the bolt that far.

DTIs Applied Bolt will make custom torque (tension) indicating washers.

Not sure if the these bolts are into a plate with threaded holes, or there are nuts being used...

To install cable clamps on suspension bridge cable (that locate the suspenders) we used a gang set of center pull hydraulic jacks connected to a manifold. First you have to draw the halves of the clamps together, then compact the main cable, then tension the bolts..pump up the jacks, then, snug up the hex nuts, pump up the jacks to design tension, snug the hex nut, relieve pressure... now repeat on the 299 other cable clamps..

The equipment we used on the Williamsburg Br was made by Biach Industries.. Biach

They were aquired by Hydratight

If you can only access one side of the fastener you can use a set of of Biachs hydraulic torque wrenchs... Hydraulic pressure would be easier to more accurately control than air and an impact type wrench...



http://www.hydratight.com/sites/defa...max-in-one.jpg


http://www.hydratight.com/sites/defa...ds/torque1.jpg

can you have sockets made that break or come apart at each torque point?

or extensions that twist apart at each torque point?

This is way more interesting than what I did at work today. :)

Not sure how limited the budget is for this problem....

But I was perusing Biachs offerings and they have come up with some pretty cool products since I last used them..

Replace the bolts with studs and use Hydraulic nuts

Apply tension to the studs simultaneously and the gasket crush can be easily controlled..

http://www.hydratight.com/sites/defa...ic_nut_1_0.jpg

I like the bolt heater method suggested by red-beard. But Inconel won't elongate much with temperature. Seems you could use the nut turns for the initial torques, then once bottomed out use a go-no-go gage as suggested above.

Changing the air pressure to change the power output of the wrench is counter to what most standards accept.. usually an impact wrench is calibrated with a fixed length of hose at a fixed pressure on a calibrated tension measuring device.. (Skidmore/Wilhelm etc)

Vary the pressure, change the length of hose and the applied torque changes..

Keep the air pressure fixed, and since it seems that this is a very controlled environment, the length of the supply is fixed also..

Use turn of nut..

You will have to determine initial torque for the fastener, and how each degree of rotation of the bolt increases the tension..

Unless you have calibrated the wrench at each pressure you have no idea what torque is being applied to the bolt..

Can you use ultrasound to measure elongation in that environment?

Yep, this has been our problem. Initially, we had a mechanical torque tester and the intent was to put it into the cell and then calibrate/validate the torque vs pressure curves prior to an operation. We didn't put the tester in the cell because we needed it outside the cell to calibrate/validate new wrenches and once something goes in - it never comes back out. We then tried an operation where we took the torque tester into an airlock room where we could bring the wrenches out and test them. That wasn't optimal because we couldn't replicate the pressure drops in the cell and then...we broke the torque tester and the manufacturer hasn't made them in a while so they balked on fixing and re-certifying it. Very few (no one?) makes totally mechanical torque testers any more and the electronic ones won't survive the radiation environment (rad-hard video scopes last about 1 hour in there).


This is intriguing. One issue in our application is that it would be difficult to contol the bolt rotation accurately and even harder to measure the amount of rotation without some special tooling.

Bingo.

Doubtful. I've used extensometers before, but don't see any way to install the transducers into the bolts (and they have to be removed as once this component is installed, it is inserted ~30 feet into a core vessel on a 200,000 lb cart so access is impossible). Our ability to do delicate work is also very limited.

I really appreciate the discussion on this as it has been a frustrating experience trying to come up with a robust way to torque these bolts. Following torquing now, we test the seal by pressuring the interstitial region between the two knife-edges with nitrogen to about 85 psi and then isolate and run a rate-of-decay test. Our allowable pressure decay is .05 psi/hr (and the volume is very low ~ 1liter, so this is a hard test to pass). Right now, if the test passes, we call it good and go on. If the leak rate is marginal, we increase the torque slightly and re-torque the bolts. To give you an idea of how difficult this is in a remote environment, torquing these bolts takes us about 5 hours (and we've gotten really good at it).

We're currently having issues as the joint passed the test during the recent installation, but is now leaking at a rate of almost 4.7 psi/hr. This seal is a liquid mercury boundary, so we're watching it closely, needless to say. We're thinking about replacing the nitrogen with helium in the seal because the extreme neutron flux is turning the nitrogen into exotic isotopes that are resulting in very high dose rates in weird places. Lotsa fun.

Since the exact torque isn't critical, a calibrated slip clutch between the driver you have now and the socket would do the trick. Something like this (there are dozens of different styles and sizes)
Hilliard Industrial Clutches, Brakes, and Oil Filtration

Wow I just realized you are doing this inside a Hot Cell
I didn't notice the manipulators in the last photo but you can see them at the edges of the photo

Slight off topic but related question. You say once something goes in it never comes out. What happens when that cell is full of junk? Did they built the room extra large in the beginning to store the hot junk? How long before it is full?

Yeah, that is really part of the problem. One of the most advanced hot cells in the world, but everything is still realy difficult.

We actually make waste shipments. In fact, we just made a shipment this week. The item we replace (called a "target") is placed in a heavily shielded transportation cask and shipped out west and buried. When we ship the cask, we throw all kinds of junk in with the target. We have to be careful what we put in the cell, though, as waste disposal regulations are very strict (and we play by the rules). Here's a picture of the transport cask (it weighs about 80,000 lbs):

http://forums.pelicanparts.com/uploa...1331133689.jpg

I guess you don't ship via UPS or Fedex ;)

I still like the strain gage idea - like the go/no-go gage suggested you could have several for the intermediate stages of tension as well. You should be able to get close using nut turns or by having a test outside the cell.

Based on the limitations he's put forward, I don't see any other solution. He just doesn't have the ability to torque with the equipment he has and most of the suggestions here still need torque. With bolt heating, you control the elongation by setting the temp, then just snug and let cool. No other measurement needed. And yes, the setup will need to be designed with Inconel in mind.

Geez, I hate machining/drilling 316! 347 and Inconel are a bear!!!