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Friction Coefficient for Steel Subsea

Friction Coefficient for Steel Subsea

Friction Coefficient for Steel Subsea

(OP)
Does anyone have information on the coefficient of friction for hard steel on hard steel subsea?  The steels will not be lubricated, but obviously they will be wet!
Any input or direction is appreciated.

RE: Friction Coefficient for Steel Subsea

Wet is wet! But data is sparse on this. Working from informtion given in Marks handbook for sled runners, my guess is that it would be about .025.

RE: Friction Coefficient for Steel Subsea

(OP)
Wow!  I was planning to go 10 times that (0.25) and be conservative.  I guess a few more details might be in order.  I am trying to clamp a tool onto the end of a casing (pipe) standing vertically.  The casing will have been subsea a long time, but condition will not be known before hand.  Coatings are unlikely, but the steel will be very hard and corrosion resistant (anodes possible, but irrelevant).  
The tool uses four hydraulic pistons @90 degrees to push 4 'shoes' onto the surface and lock it. The clamps will be used to counteract the torque the tool will apply to the casing. The shoes will actually have a sharp facets, so in fact it will be more of a hardness/biting question; but since I have no way to analyze that mathematically, I was going to be conservative and just use a friction force.
I don't know if that changes your answer, but at least you understand the application now.

RE: Friction Coefficient for Steel Subsea

If you're only rotating in one direction how about using something similar to power tongs. Pads on cams so that as you rotate they increase their engagement. You could reduce your rams to one, or use two for redundancy. Trick would be to design your cams so they don't crush your casing below drift.

RE: Friction Coefficient for Steel Subsea

According to Machinery's Handbook, Steel on Steel is 0.8 static unlubricated, and 0.16 static lubricated.  Sliding friction would be 0.4 and 0.03 respectfuly.  Generic, but hope it helps.

"Happy the Hare at morning for she is ignorant to the Hunter's waking thoughts."

RE: Friction Coefficient for Steel Subsea

Actually you can analyze the grip force due to digging into the material if you have some idea of the relative strengths of the materials.
Calculate (or even measure) the penetration depth of your gripper facets, this will give you an area. Calculate the shear at this area when you torque the tool to remove the pipe. Multiply times the number of grips.

If your pipe diameter is consistent I would think a locking tool approach might be worth looking at. Have you ever seen an automotive stud remover?

You could also take a look at a monkey wrench to see how best to take advantage of the effect.

Crashj 'on the Internet no one knows you are a monkey' Johnson

RE: Friction Coefficient for Steel Subsea

(OP)
Thanks guys.  Good replies all.
The pipe diameter will not be consistent, so the tool will need to adapt from 13" to 36" diameters.  Once I have built the tool I can empirically test the grip force - measuring the penetration depth would be a good idea.  The cams are also a good idea.  I'll need to look at that.
I'm still not convinced though that 'wet' steel will perform similiar to 'greasy' or 'lubricated' steel.  I guess I might have to do some tests and let everyone know in the future.
Thanks again.
-DeepBlues

RE: Friction Coefficient for Steel Subsea

You have made a wise decision to TEST.
Good luck!

Pat

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