Dear alk,
I plan to make some orifice flowmeters of my refinery checked, during the next shutdown.
I was wondering if you could share your experience and knowledge regarding the "things" to be checked to ensure optimal accuracy of the existing orifice flowmeters?
Also, what documents shall I request from the instrument mechanics in charge of the check, in order to keep track of what have been done and to verify that the job has been done professionally?

"We don't believe things because they are true, things are true because we believe them."

Hi Sheiko,

I should check at least these values:

- flatness of the orrice place
-edge - should not reflect light
-thickness
-roughness
-angle of bevel
-concentricity
- diameter

Keep a record of all those values. If some of them are out of the limits then you should replace or send the orrifice place for rectification. You can use ISO 5167: 1991/2003 for guidelines.

Bogdan

I want people to check most of those things every calibration. For a turnaround I want to get serious

Drop the end caps and visually inspect the tube
Look for debris around the plate holder
Uneven surface wear (e.g., look for a rust channel upstream of the plate)
Surface roughness
Condition of vanes or flow conditioner (I once found a quarter of a mist pad in the vanes on a meter tube).

If the tubes don't have end caps (and many don't), I would pull the tube out and inspect it on a bench

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

In addition you should check the face of the orifice plate for contamination – lube oil, grease, dust, etc and any damage to the upstream face. You could also check the orientation of the plate, it’s not so uncommon to find a plate that has been installed the wrong way round. Quite often sites will take photographs of the plates, typically these are more for inspection reports but could be a useful record especially if there is a history of contaminated plates