I have an incorrect orifice installation in my plant but i can't correct the same as it needs complete shutdown of the whole plant.

What error in measurement happens if an orifice plate is installed in reverse direction, i.e. the bevelled edge in upstream side? can somebody help? how can i estimate the error for such an installaton. I need to quantify the same as i can't correct the installation before the next major shutdown of my plant.

regards,
DK
[email protected]

 

Like my friend David says, you can shop for answers.

1) Here you can read about the nuclear's industry gaffs installing OP's backwards citing 15% error:

http://www.nrc.gov/reading-rm/doc-collections/gen-comm/info-notices/1990/in90065.html

2) Control Engineering's article uses 20%

Reversed plates are simply those installed with the sharp orifice edge on the exit or downstream side of the plate. Depending on the beta ratio, errors introduced by reversed plates can be as much as 20%.

http://www.controleng.com/article/CA188313.html

3) Here's a paper that claims up to 25% error with a plate installed backwards: (pg 2, 2nd column)

Edge rounding or the plate in backwards has the same general effect with differing magnitudes. The backward plate under registers flow as high as 25%, the rounding of the edge is dependent on the magnitude of rounding.

http://www.ceesi.com/docs_techlib/events/ishm2005/Docs/1190.pdf

4) White paper:
That is that in each condition the meter is under registering. The actual flow rate exceeds the
indicated flow rate. That means unaccounted for gas. The following data was derived from several independent tests performed by Nova Gas Transmission, CESSI, GRI, Chevron Petroleum and UK National Engineering Laboratories.

Plate installed backwards 8 to 25 -Error %

http://www.cga.ca/events/documents/bell.pdf (pgs 6-7)

5) Good News: Rosemount's statement about bias is probably true:

installing an orifice plate backwards or with insufficient straight pipe will cause additional flow error – usually introducing a bias error and affecting accuracy rather than repeatability.

http://www.emersonprocess.com/Rosemount/support/papers/chemical0810.doc (pg 7)

6) And the Great News is, someone's actually tried to estimate the error:

Backwards-Facing Beveled Orifice Plates

A related topic is the backwards installation of a beveled orifice plate. When an orifice plate is accidentally installed backwards (with the beveled edge upstream and the square edge facing downstream), the pressure drop across the plate is reduced, and the flow rate can be under-registered by as much as 20 percent. Morrow and George, [5] among others, demonstrated that a backwards-facing orifice plate causes a measurement error that is a function of the following.

·Orifice beta ratio, b

· The ratio of orifice bore to plate thickness, e/E

· The ratio of orifice plate thickness to meter tube diameter, E/Dnom

· Reynolds number

Figure 2 compares backwards-facing orifice plate test data from the Gas Technology Institute Metering Research Facility with results from Ting [6] and Witte. [7]

Morrow and George have proposed the following correlation for a backwards-facing orifice plate to estimate the percentage measurement error as a function of the beta ratio, b, plate thickness to meter tube diameter ratio, E/Dnom, and bore thickness to plate thickness ratio, e/E.

%DQ = -18.93 + 12.91b - 34.04 (E/Dnom) – 8.900 (e/E) + 13.64 (e/E)2

http://phd.iqsoft.co.in/GasHydrate/Experiment/orifice meter/Orifice Meter Accuracy.htm

Carl