Effects of extreme pressure on materials

[nrobidoux]

TL;DR Summary

Design a 3D printed part to survive 8k psi (~55 MPa)

This is a project I gave myself at work, really just to improve things. It didn't come from above but from myself. However I went the route of biological and computer sciences not engineering.

Without going into excruciating detail essentially a plastic "tube" will be going into an oil well. This is a 3D printed part that is meant to slide over the shaft of another and take up nearly all the space in the well bore.

Would be approximately 26mm thick, 100mm diameter, with a 50mm hole offset from center for the shift.

Initially this was going to be a solid piece. But I thought perhaps it might be better to have the internal cavity hollow with:

A.) 3D lattice for support internally (cubic arranged so 2 corners align top to bottom; or rhombic dodecahedron)

B.) Small equalization holes

C.) Instead of 1" max thickness, 0.25" was arbitrarily chosen for exterior surface and minimum 1/8" for lattice

These are all my ideas and I have no idea if any are effective in helping the part survive. My thought process was essentially any effect is multiplied as the thickness increases so minimize the thickness but still provide structures to maintain strength. But I'm not sure if doing these things introduces new challenges

It has to be 100% infill because at even normal well pressure any air gaps will collapse (I would think...) so normal 3D printing with x% infill I don't think would cut it. (The infill also produces a lot of air filled cavities...)

I'm probably going to print the final part with all perimeters (vs 3 perimeters than linear fill) to minimize the extremely small cavities produced by standard printing.

I'm not sure how to use these numbers which should be representative of the material currently being considered (polycarbonate blend with carbon fiber). I can't find the technical data sheet on the supplier's site. Should be in the ball park. I attached a small image of that sheet.

Can the part survive the pressure? Is one better then the other or both essentially equivalent except for material cost and print time?

It will also be operating at/ near its glass transition temperature (either side).

 

[Baluncore]

Why not fabricate it partly from rubber and fill it with silicone oil ?
Then it will not be crushed and water will not enter.

 

[nrobidoux]

This part exists. Rubber works great a few times. Then you need a new part. It also has the hole centered. Not offset. That's really where the wear comes from. Plus we need an insert to narrow down the ID of the rubber part to fit on the shaft properly.

Be nice to just print-n-go so to speak.

Getting a custom rubber part... honestly I don't think anyone's considered it. Plus once the cost is determined probably would discard the idea. Because it's custom and not mass produced

 

[nrobidoux]

The rubber is crushed also... but it has the give in it to survive. If it wasn't clear on my original post that was my first inclination: solid part like the original. Then my mind got involved and asked is it easier on the material if a smaller thickness was used and to accommodate that: equalization holes and an internal 3D support lattice came into play.

 

[Baluncore]

Summary: Design a 3D printed part to survive 8k psi (~55 MPa)

Can the part survive the pressure?

The material can survive, but the air bubbles are a problem.

You could prevent distortion by drilling the material full of small holes, it will quickly vent air and fill with fluid. An open cell foam would do the same without the drilling.

Cast it from a resin that has been vacuum treated to remove air bubbles.

Maybe you could explain the reason why you need to sink this eccentric device down a deep borehole.

 

[nrobidoux]

The material can survive, but the air bubbles are a problem.

You could prevent distortion by drilling the material full of small holes...

Maybe you could explain the reason why you need to sink this eccentric device down a deep borehole.

It's a potential business thing hence the secrecy. But another thread fished more info out of me. Pics weren't enough to get the principle across, LoL. Well I think they were trying to go past that and see if the actual use case would provide any more info... no.

I'd like to avoid creating a solid piece for a few reasons other than my brain being ignorant of the physics involved. So I was going to create an internal support lattice. I'm just finding it difficult to model. Lack of knowledge in Blender. The model is beyond the position to be printed as a solid piece. This lattice wouldn't have enclosed spaces.

There would be small holes in the model to allow for equalization. I already have lots of ideas for improvement and I haven't even released version 1.0. :)

Honestly I probably don't need the lattice with the current thickness, it's more for the large overhang gap and lack of support material... although... I guess I could just forego the lattice use the supports and let them get crushed... the model is in this position.

Then I return my ignorance of materials (prefer lattice over cavity in such a state) because I don't know how to calculate if this hollow structure can withstand the shear/flex of water traveling 12-16 mph used to push a 700+ lb 3.125" steel cylinder in a 4" ID steel tube.

 

[jrmichler]

So you want to push a 700 lb 3.125" diameter steel cylinder in a 4" ID pipe full of water. Is the cylinder traveling upward, downward, or horizontally? Does the cylinder need to move at the same speed as the water?
If the cylinder is traveling horizontally or upward, then you can calculate the force to push it, and the necessary pressure difference across the pusher. If the cylinder is traveling downward, does the pusher need to hold it back to the same speed as the water? If so, calculate the force and pressure difference across the pusher. Does it travel upward, downward, and horizontal in the same run?

If the cylinder needs to move at the same speed as the water, then the pusher needs a sliding seal to the steel pipe. And we need to know the surface finish of the inside of the pipe - is it smooth steel, standard Schedule 40/80/160, or rusted crusted rough steel? What is the total travel distance? If the pusher is cheap enough, can you use it once and discard it? Does the pipe have fittings, valves, and elbow that could snag the pusher? Is the cylinder one rigid piece, or is it jointed to flex around elbows?

Try search term pipeline pig to look at solutions to a very similar problem.

 

[Baluncore]

The material and construction are determined by application.
We are blind guessing here.

I think the device must be an eccentric guide, like a loose fitting piston.
Is it attached to the 3" steel cylinder? How?

I cannot see how water pressure, or flow, can push a loose piston into a well that contains water. Is there a mud-motor being driven by an axial fluid flow?

As it sinks down the well, the fluid in the well will need to be displaced around the 3” cylinder. Is 12-16 mph the rate of descent, or is that the water speed in the narrow gap between the cylinder and the well casing, or the device and the well casing.

 

[nrobidoux]

The toolstring has several angled surfaces that eventually reach 3.125". Might be something like:

45 deg from 0 - 2" diameter
1' - 2"
60 deg from 2" - 2.75" diameter
25' - 2.75"
90 deg 2.75" - 2"
2" - 2" (goes here)
90 deg 2" - 3.125"
20' - 3.125"
Steps down 3.125" - 2.75"
5' - 2.75"
45 deg 2.75" - 3.8"
2' 3.8"

This is attached to a wireline cable. The rubber piece we use goes in the same place... honestly a rubber piece might be fine with slight modifications but no one is going to pay for its creation... and I can't prototype a rubber part. ... And I have all these ideas already for improvements once I get a dual extruder printer... or Prusa's Multimaterial Unit...

Water is pushed into the well... pressure may start 4000 - 6000 psi and during this process get to 6000 - 9000 psi. I just did a linear extrapolation, best guess in my head, to get to 12-16 mph. That would be laminar flow in open casing. I did do the calculation many times for 80 bbls/min in 4 inch... that is ~ 58mph laminar flow. Just came down from there.

This piece is optional but decreases the amount of water needed to get to depth... vertical depth ~10k' ; horizontal out to another 10k'. Typically used only in horizontal. Gravity does the work vertical. Tool string travels 100 - 500'/min horizontally... Can go faster but not with the current selection of tools the client has. Typically the wireline is holding the toolstring back slightly.

I'm not sure about the price of the rubber part. But simple things can be expensive... I picked up 50 threaded plugs to cap holes in the older style tool strings... metal... ~1.25" x 0.75" ... $3000. The idea behind this pusher is to not discard it after one run.

I keep purchasing things to upgrade my printer but at the moment I can only print the plastic I attached the sheet up top for. Open to explore other materials later... but stuck with this one currently.