2 replies to this topic

[deltaChe]

How to choose the appropriate pressure gauge to meet process & I&C engineer requirement.

We process engineer deign a pressure gauge installed on the process line (liquid phase, line pressure is min op= atm, normal op=1 barg,max op=12 barg, and design pressure=25 barg).

But, the I&C staff came to me and said this pressure gauge maximum op should be within the two third of the maximum full scale of the gauge. So in this case max op should be 2/3 X 12 barg=7.9barg instead of 12barg.

As I know every pressure gauge have an inherent over range generally 1.3 times the maximum full scale value of the gauge.

My question is how to fix the I&C staff problem to choose the appropriate pressure gauge and also meet process staff requirement max op=12 barg.(for example put two pressure gauge)

Thank you very much.

Edited by hswang2, 04 July 2010 - 12:08 AM.

[fallah]

Normally pressure gauge ranges should be selected such that normal working pressure will be between 50% and 80% of calibrated range and should be capable of withstanding over-pressure up to 1.3 time the prevailing design pressure or relieving pressure of the equipment.

How much is the full scale value of the selected gauge? 12 barg?

How much is the calibrated range of the selected gauge?

Seems the difference between normal operating pressure and maximum operating pressure and on the other hand between operating/design pressure are more than usual and need to be rechecked.

[djack77494]

But, the I&C staff came to me and said this pressure gauge maximum op should be within the two third of the maximum full scale of the gauge. So in this case max op should be 2/3 X 12 barg=7.9barg instead of 12barg.

I think you have misinterpreted what the I&C staff told you. Instead of saying that the max op should be 7.9barg, you should calculate the upper end of your pressure gauge's scale as being:
12barg / 2/3 = 18barg.
Since gauges usually come in even denominations, you may need to buy a 20 or 25barg gauge.

But more important than just mentioning general purpose "rules" would be for YOU to determine what range of pressures it is important to measure. Do you want to only know about the upper end when you are approaching the design pressure? Or do you care a lot more about your normal operating pressure? In the latter case, you can purchase a gauge with a fairly narrow range, let's say 0 to 2barg. Now, throw away your "rule of thumb" that says the gauge will explode at 1.3 * the full scale range, and just specify that the gauge will occassionally see pressures as high as 12 to 25barg. Then check that the I&C people actually purchase such a gauge.

Edited by djack77494, 06 July 2010 - 04:32 PM.