What equipment to measure force applied to ID of pipe?

[boostedda]

Hello PF. I'm currently tackling a problem at work that I could use some input on.

I am trying to gather data regarding the force applied by a swelling material against the ID of a pipe. The purpose is to determine how the force increases with swell before leveling off, as well as to see how uniform this force is throughout the material.

The biggest issue seems to be the environment that the testing is performed in. I need something that will withstand high salinity water heated to 80* C for a prolonged period of time (3 weeks ish.)

I've considered using strain gauges placed on the OD of the pipe, but I don't believe the force generated by the swelling material will be large enough to read on a metal pipe. I would need to determine a material that would deform enough for the strain gauge to read as well as withstand the environment. I'm also not sure if strain gauges are designed to be submersed or exposed to salt water.

I've considered flexible force sensors attached to the ID wall, but they are not submersible nor designed for salt water.

Is there a way to use a piezo material (think quartz tube) to measure this? I'm still an undergrad ME student so my real world engineering experience is limited. Any input is appreciated.

Thanks,
Chris H.

 

[Dr. Courtney]

Not much is really guaranteed for harsh environments without paying through the nose for it.

I'd use a strain gage that can handle the temperature and then ensure all the sensitive elements were protected from the salt water.

 

[Baluncore]

The purpose is to determine how the force increases with swell before leveling off, as well as to see how uniform this force is throughout the material.

Is the content a liquid?
If so, then why not use a simple pressure gauge.

What material is "throughout the material", the pipe or the expanding content.

The outside of the pipe will also stretch when under pressure. You could place strain gauges on the external surface, then calibrate with water and a pressure gauge.

 

[boostedda]

Not much is really guaranteed for harsh environments without paying through the nose for it.

I'd use a strain gage that can handle the temperature and then ensure all the sensitive elements were protected from the salt water.

That is one of the ideas I'm juggling at the moment and may be the route I end up going.

Is the content a liquid?
If so, then why not use a simple pressure gauge.

What material is "throughout the material", the pipe or the expanding content.

The outside of the pipe will also stretch when under pressure. You could place strain gauges on the external surface, then calibrate with water and a pressure gauge.

The swelling material is rubber that is activated by salt water, and because of the environment/characteristics of the rubber, I would like to determine if the rubber is swelling uniformly inside of the pipe. So to answer your question, "throughout the material" refers to the expanding content.
As of now, the material is placed inside of a 2" ID Schedule 40 pipe. The swelling material is not going to generate enough force for the strain gauges to read any change on the OD of the pipe. Moving to another material for the pipe/tube is an option. I'm not sure what materials will keep the swelling rubber contrained to a 2" diameter but still deform enough for the strain gauge to read a change on the OD - all while withstanding the prolonged exposure to high temp salt water.

Thanks for the replies.

 

[Baluncore]

Does the rubber fill the tube or is it only a lining on the internal wall of the pipe?
Usually rubber will flow to equilibrate pressure. How hard is the rubber?
You might be able to use an ultrasonic reflection depth gauge from outside the pipe.

 

[boostedda]

Does the rubber fill the tube or is it only a lining on the internal wall of the pipe?
Usually rubber will flow to equilibrate pressure. How hard is the rubber?
You might be able to use an ultrasonic reflection depth gauge from outside the pipe.

There exists a small gap between the OD of the rubber and then ID of the pipe. The rubber will swell to fill the gap creating a "seal." The durometer of the rubber varies based on the different batches I'm testing. That is part of the reason for measuring the force - to determine the different characteristics between the batches.

 

[Baluncore]

If the OD_rubber to ID_pipe gap is filled with brine then measurement of the thickness of that annulus at a few points around the pipe will answer the question. That can be done from outside the pipe with an ultrasonic gauge. There should be big differences between the acoustic impedance of pipe, brine and rubber.

 

[boostedda]

The rubber makes contact with the ID and continues to swell internally (at a lesser rate due to less exposed surface area for water transport) such that the force continues to climb before leveling off. How would I derive this force curve using an ultrasonic gauge?

I'm understanding the ultrasonic setup to transmit sound waves through a medium and receive the reflected wave to measure depth or distance. How would this correlate to force applied to the wall from the rubber and more so how that force levels off after contact? Also, with a material like rubber would one run into issues with sound absorption?

 

[Jeff Rosenbury]

How stable is the temperature? I suspect most force sensors will drift with changing temperature (as will the pressure I think).

Is this natural rubber?

 

[Jeff Rosenbury]

You mentioned you might be willing to change pipe materials, so here's a solution. It's not simple or cheap, but it should work.

Place a deformable plastic sleeve inside a non-deformable outer pipe.

If you make the sleeve out of a clear plastic like Lexan (which softens at about 80º C) and the outer pipe out of something clear like borosilicate, you should be able to visually check the deformation. (Put some color in the plastic.) Other plastics might be used to get whatever effect you want. With a proper choice of plastic, interference patterns might be achieved.

I'm not a materials expert, perhaps someone else could suggest better materials.

You will still need to keep careful track of the temperature to tare its effects on the plastic.

 

[boostedda]

I ended up using a split casing design with the top half of the casing connected to a load cell placed outside of the solution.

Thanks for the replies!

 

[Nidum]

(1) Take the measuring system out of the brine . Attach pairs of rigid rods to tube and put sensing devices out in fresh air at other end .

(2) Devise a mechanism which has a touch probe and an anvil arranged to contact tube on a diameter with a pivot in manner of a finger dial gauge . Again put the actual sensing devices in fresh air . Can be arranged to magnify movement .

(3) Make a micrometer with two long legs on it and measure manually once per day .

Need to watch temperature effects and rigidity in implementing any of above but all three methods have been successfully used before .

NB: For each sampling measure a plain inactive piece of tube in same brine solution at same time as measuring actual test section .