The document details flow measurement technologies, specifically focusing on orifice plates as the predominant technique used in refineries, accounting for about 90% of flow meters. It discusses basic equations governing flow, installation requirements for orifice and venturi meters, and factors affecting measurement rangeability. Additionally, it covers the necessity of vent and drain holes to manage unwanted liquid or gas during measurement.

1. Flow Measurement Technologies: Orifice Plate
Learning Session-03

2. Flow measurement
In our refinery most common flow measurement technique is
Orifice. (Almost 90% Flow meters are Orifice Plate based)
Flow Measurement : Orifice Plate
Orifice Plate and Flange Flow Profile through Orifice

3. HPCL MR: Instrumentation in GFEC
HPCL MR: Instrumentation in GFEC
Obstruction Meters
• Orifice Meters
• Venturi Meters
• Flow Nozzles

4. Flow through a Nozzle
2
2
1
1
2
1
2
2
2
1
1
1
2
1
v
A
v
A
ible
incompress
v
A
v
A
Av
m
m
m













1
1
1
1
v
A
m


2
2
2
2
v
A
m


Basic Equations:
a.) Continuity:
mass in = mass out
b.) Bernoulli’s Eqn.
Total pressure is constant
throughout

5. pressure
dynamic
v
2
1
pressure
total
P
pressure
static
P
P
P
v
2
1
P
v
2
1
P
v
2
1
.
const
essure
Pr
Total
P
Bernoulli
2
0
0
2
2
2
2
1
2
1
1
2
0















Flow through a Nozzle
Flow through a Nozzle

6. 




































P
2
A
A
1
1
YCA
Q
Flow
al
Re
For
Ideal
P
2
A
A
1
1
A
v
A
Q
Rate
Flow
P
2
A
A
1
1
v
2
1
2
2
2
1
2
2
2
2
2
1
2
2
Flow through a Nozzle

7. 7#
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60 70 80 90 100
METER RANGEABILITY
METER RANGEABILITY
NORMA
L
RANGE
% MAXIMUM FLOW RATE
%
MAXIMUM
METER
HEAD
The square root function’s impact on a differential pressure device limits
the measurement turndown (rangeability) to between 4:1 and 6:1.

8. Installation
• The Minimum Straight Lengths of Pipe Required between
Various Fittings and an Orifice Plate or Venturi Tube (as
recommended in ISO 5167-1) to Ensure That a Fully
Developed Flow Profile Exists in the Measurement Section. All
Lengths Are Multiples of the Pipe Diameter

9. 9#
PIP PCCFL001
STRAIGHT RUN REQUIREMENTS
PIP PCCFL001 includes tables for
minimum straight run lengths with
various upstream disturbances,
providing upstream requirements for
different beta ratios and downstream
requirements per beta ratios
regardless of upstream disturbance
type.

10. 10#
VENT AND WEEP HOLES
There are times when a gas may be have a
small amount of liquid or a liquid may have a
small amount of gas but not enough in either
case to warrant the use of an eccentric orifice.
In these cases it is best to simply add a small
hole near the edge of the plate, flush with the
inside diameter of the pipe, allowing undesired
substances to pass through the plate rather than
collect on the upstream side. If such a hole is
oriented upward to pass vapor bubbles, it is
called a vent hole. If the hole is oriented
downward to pass liquid droplets, it is called a
drain hole.
VENT
DRAIN