Best way to measure non-thermal expansion of a pipe

[Jehannum]

TL;DR Summary

I need a highly-accurate method of measuring the diameter or circumference expansion of a pipe undergoing pressurisation.

Ideally, the method should be accurate down to 0.01 millimetres or better.

We're probably talking pipes of up to 150 mm (6") diameter.

Accurately measuring the actual diameter of the pipe is of less importance - it's how much it expands that matters.

My idea is wrapping something around the pipe with an "emitter" and a "sensor" at opposite ends that will be pulled apart as the pipe expands. The sensor can accurately measure its separation from the emitter. The expansion will be so small it can probably be regarded as a simple linear distance.

Is there any reasonably-priced equipment that can be adapted to this purpose?

 

[jrmichler]

0.01 mm is 0.0004". A good micrometer will easily measure that accurately. Here's one source: https://www.mscdirect.com/browse/tn...d=4287924594+4288246876&searchterm=micrometer.

If you want to make automated measurements, look at strain gauges: https://micro-measurements.com/. Be advised that learning how to apply and use strain gauges by reading the Micro-Measurements catalog will have a loooong learning curve.

 

[Jehannum]

Thanks.

I think I would have to describe the measurement as "automated". The measuring device would have to stay in exactly the same place and not be touched until the end of the test (partly down to safety reasons - i.e. exclusion zone).

As far as I understand it, a micrometer can't work this way - i.e. with a dynamically-changing measurement. It has to be manually adjusted for each measurement taken.

I'll read up on strain gauges then!

 

[OCR]

If you want to make automated measurements, look at strain gauges: https://micro-measurements.com/. Be advised that learning how to apply and use strain gauges by reading the Micro-Measurements catalog will have a loooong learning curve.

That seems to be a very informative site. . . thank you for the link. . Also, did anybody notice ?

Lol, a while back, we had a small discussion about that subject. . . right here. .

Cold welding | Physics Forums
.

 

[jrmichler]

I think I would have to describe the measurement as "automated". The measuring device would have to stay in exactly the same place and not be touched until the end of the test (partly down to safety reasons - i.e. exclusion zone).

There's another way to measure changes in pipe diameter electronically. Build a fixture similar to the sketch, and use an inductive analog proximity sensor.

An inductive prox sensor sends out a voltage proportional to the distance from the end of the sensor to a metal object. Here's one that could meet your needs: https://www.omega.com/en-us/sensors...mity-sensors/iprox-series/p/E59-M12A105C02-D1.

I have used a similar sensor. In a room temperature environment, it would reliably and repeatably read to the limits of a 12 bit A/D converter. That would be about 4 mm / 4096 = 0.001 mm.

You would need to design a stiff and solidly mounted mounting bracket. You will need to consider the effects of temperature variation on the mounting bracket. If you go this way, do some experimenting by touching the mounting bracket with a finger and note just how much you move it by pushing, and by the effects of finger warming.

Big advantage is that the learning curve is much shorter than with strain gages (which I spell either way depending on my mood at the time).

 

[MRFMengineer]

There's another way to measure changes in pipe diameter electronically. Build a fixture similar to the sketch, and use an inductive analog proximity sensor.
View attachment 269905

An inductive prox sensor sends out a voltage proportional to the distance from the end of the sensor to a metal object. Here's one that could meet your needs: https://www.omega.com/en-us/sensors...mity-sensors/iprox-series/p/E59-M12A105C02-D1.

I have used a similar sensor. In a room temperature environment, it would reliably and repeatably read to the limits of a 12 bit A/D converter. That would be about 4 mm / 4096 = 0.001 mm.

You would need to design a stiff and solidly mounted mounting bracket. You will need to consider the effects of temperature variation on the mounting bracket. If you go this way, do some experimenting by touching the mounting bracket with a finger and note just how much you move it by pushing, and by the effects of finger warming.

Big advantage is that the learning curve is much shorter than with strain gages (which I spell either way depending on my mood at the time).

This is how I would do it. You could also use a digital dial indicator or linear gage.

 

[Baluncore]

I don't expect this will help but; winding an optic fibre around the pipe would make for very high resolution. The fibre will stretch and shrink as the pipe expands and contracts. That changes the length of the optical path. Use the optical interferometer and electronics from a Fiber Optic Gyroscope, FOG. Unless you orientate the axis carefully E-W, you will detect the continuous rotation of the Earth.