| January
2003
What
you should know:
EUB to implement AGA3, 2000 for Orifice Meter Runs
 The Alberta Energy
and Utilities Board has released a revised draft copy of
Guide 46 titled “Production Audit Handbook”.
Under subtitle “Meter Run Inspection” for orifice plates,
the guide states meter runs installed at receipt points after January 2003 should
conform to AGA 3, 4th edition, Part 2, Section 2.6
specifications. The report outlines the required upstream and downstream pipe diameters now
required for an AGA approved orifice meter run, and includes
various piping scenarios with and without an approved
flow-conditioning device. It
is believed Measurement Canada will also soon adopt the revision.
API and AGA have
undergone extensive testing proving flow
conditioners re-create the flowing conditions required to accurately
replicate the orifice plate coefficient of discharge database
values. In other words,
they eliminate bias in orifice plate measurement.
Flow conditioners effectively remove the swirl component in a
flowing stream which can impact the overall measurement of the
primary device. Flow
straighteners, unlike flow conditioners, are not as effective in
producing the flowing conditions necessary to replicate laboratory
conditions and require increased meter tube lengths. When the
American Gas Association revised Report No. 3, they outlined the
minimum required lengths for meter tubes with and without flow
conditioners. For
example, without a flow conditioner, a meter run manufactured for
installation in any configuration, also referred to as the “catch
all” category, now requires a minimum unobstructed meter tube
length upstream of the orifice plate equal to 145 pipe diameters.
That is for beta ratios of 0.40 to 0.75.
When using an approved flow conditioner, the minimum distance
for the same application is reduced to 11.5 pipe diameters.
Two 90 degree elbows in perpendicular planes prior to the
meter run now requires 50 – 95 pipe diameters upstream of the
orifice plate when the separation distance between piping elements
is less then 5 diameters. With
an approved flow conditioner, the minimum distance is reduced to 5
– 14.5 pipe diameters depending on the beta ratio.
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It is clear flow conditioners considerably reduce the length of straight pipe now required upstream of an orifice plate. Until now, there has not been a governing
body in Alberta inspecting to AGA 2000.
Producers, fabricators, and EPC’s should be aware of this
change. CB Engineering
represents Savant Measurement Corporation, who manufactures the
Gallagher flow conditioner, and would be happy to further discuss
this issue and how best to implement these changes.
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