HOW TO IDENTIFY THE CALIBRATION PERIODS OF THE ROTARY METERS... ISTANBUL BY EXAMINING PRESURE LOSSES

HOW TO IDENTIFY THE CALIBRATION PERIODS OF THE ROTARY METERS OPERATIONAL IN
ISTANBUL BY EXAMINING PRESURE LOSSES
Ahmet YETĐK
[email protected]
Serkan KELEŞER
[email protected]
A.Abdulkadir AKGÜNGÖR
[email protected]
INTRODUCTION
There is no doubt that metrology has an important role in economy, industry, production as well as in
our daily life. With its scientific, commercial, ethical and social implications, accurate and reliable
measuring is so important that, if failed, will create technical and social problems affecting families,
communities, regions, nations, and international relationships. In the industrialized countries, the
accuracy and reliability of measurements are tested according to a nation wide web of calibrations.
According to one definition calibration is “a series of operations that under certain conditions helps to
identify the difference between a value on a measuring device and the value that it should show
according to a given reference”.
A gas distribution company is responsible for accurate measuring and accurate billing of the gas sold.
Accurate and reliable measurement is crucial for both the distribution company and the consumer.
We can classify gas measurement into three groups: industrial, commercial and residential. Major gas
measurement devices are rotary meters, turbine meters and diaphragm meters. Amongst them,
diaphragm meters are used at houses, whereas rotary and turbine meters are used by the businesses
and industry. There are particular problems associated with the use of these three types of meters.
This article aims to examine the pressure loss of rotary meters being used in Istanbul, without
removing them, and demonstrate the relationship between pressure loss and calibration.
The method we are going to use involves connecting a sensitive manometer onto the input and output
pressure connections in order to obtain the pressure difference between the input and output
connections of the rotary meter, while gas continues to flow through. Then, the obtained results are
compared with the reference values to indicate the extent of pressure loss at that particular meter.
The results will offer us an insight to the measurement levels of the rotary meters being used in
Istanbul. They will also have reflections with regards to the calibration of the rotary meters. The meters
with a pressure loss beyond the standard value appear to have more problems when calibrating. While
demonstrating the calibration status of the existing rotary meters in Istanbul, this study will also provide
a point of reference for EU and other countries on our continent. While in some European Countries
the rotary meters are calibrated every 16 years, it is 10 years in Turkey. This study will provide clear
outcomes on the required calibration periods for the rotary meters. The study will also have
implications on the gas pollution and reducing such pollution.
This article will focus on and analyse the rotary meters being used in Istanbul, while its findings will
help demonstrating the relationship between pressure loss and calibration.
APPLICATION
Figure1.The inside of Rotarymeter
inlet
outlet
Figure.2.Rotarymeter working principle
Pressure problems were experienced where rotary meters supplied gas at low pressure to snapacting loads. The impellers. inertia could first cause a pressure buildup and then create inadequate
pressure due to reversal of the impellers. This caused pilot outage. In most cases, a check valve
downstream of the meter solved this problem. Since the changes to aluminum to reduce inertia on
new rotary meters, thousands of rotaries have been installed on low-pressure applications with
minimal problems
A differential rate test should be performed when the meter is first installed and under the actual
conditions of gas line pressure and specific gravity that will exist in service. This test consists of a
series of differential pressure readings taken between the inlet and outlet of the meter at several gas
flow rates within the meters range of capacity.
The test is particularly important when line pressure will be higher than 15 mbar, so that direct
comparison with later tests can be made. Below 15 mbar, the field tests on gas can be compared
directly with factory test results on air obtained from an individual referencemeter test curve or a
characteristic accuracy curve. In either case, an increase of up to 50% in differential pressure at any
flow rate can be tolerated without affecting the meter accuracy more than 1%. This has been proven
by exhaustive factory and field tests.[1]
Conducting the Differential Rate Test
1. Pressurize the meter by slowly opening the inlet and discharge valves.
2. Adjust the bypass and the inlet valves until the meter operates at a selected flow rate in the
lower range of its capacity.
3. With flow stabilized, time the passage of a predetermined volume of gas as registered on the
counter or instrument.
4. Record the differential pressure reading, line pressure,
5.
Repeat the test several times to obtain an accurate average reading.
6.
Obtain similar differential readings at as many different flow rates as possible within the
meters range. At least three points are required within the 25% to 100% range to establish
data for an accurate curve.
7. Convert the gas flow to displaced CFH, and plot a curve of differential pressure versus flow
rate.
The meter condition and performance can be checked periodically by running a similar differential
rate test at a single selected point. If the differential pressure has increased by 50% or more over the
original reading at this rate, check the meter for causes of increased resistance. valve grease, pipeline
dirt, worn bearings, and too heavy or too much oil.
Accompanying new meters is a test data sheet stating the meter accuracy at the flow rates agreed
upon by the manufacturer and the utility (usually 10% and 100% of capacity.) This sheet establishes
the normal pressure differential at the existing conditions of flow rate (meter speed), line pressure and
gas specific gravity, for comparison with future tests. Later increases in differential pressure indicates
worn bearings or a build-up of foreign deposits on impellers or casing. The differential pressure at a
given meter speed is a function of the gas specific gravity and line pressure. An increase in line
pressure or specific gravity increases the differential. Thus, the same test conditions must be
maintained in later tests to permit direct comparison with the original test.
Mechanical drag is the primary factor that can affect the proof of rotary meters. A significant increase
in rotating resistance requires more gas energy to turn the impellers, and a greater pressure drop
across is indicated across the meter. Thus, the differential-rate test is accepted by many state utility
commissions as a means of periodically substantiating the original accuracy of a meter as represented
by the curve of a factory-performed referencemeter prover test[1][3][4].
THE FORMULATION OF PRESSURE LOSS
2
∆ P2 = ∆ P1 x d(Pm / Patm) x (Q / Qmax)
∆ P2 = Pressure loss
∆ P1 = Pressure loss according to flow and meter type
Pe = Operational pressure
Pm = Mutlak Basınç
Patm = Atmospheric pressure
Pm = Pe + Patm
Q = Project flow
Qmax = Maximum flow according to meter type
3
3
d = Air density = 1 kg/m
Natural gas = 0,6 kg/m
The data necessary to calculate the loss of pressure are the flow data and the meter data[2]
Table 1.The choice of pressure loss for Rotarymeter
Another pressure loss calculation method Schlumberger(Actaris)[2]
ISTANBUL STUDY
In the study every single meter in Istanbul in the Bosphorus region was examined .In the study a total
of 711 meters were examined .The measurement interval of these meters is 1:20 There were
lubrication problems with 458 meters. The wrong type of lubricant had been chosen. 256 meters
suffered from faulty installation. The customers in question were notified in writing and requested to
correct their installations in the event of not correcting the installation of their meters they were further
informed that their natural gas supply would be cut off . In general the pressure of the meters
examined is between 21 mbar and 300 mbar. Some examples of the study is provided below.
MEASUREMENT OF PRESSURE LOSS
All the meters suffering from lubrication problems and those installed improperly in the Bosphorus
region had their pressures checked. The meters with the highest loss of pressure were uninstalled and
recalibrated .Below the pressure loss measurement method is shown.
Diagram3. Rotarymeter pressure loss measurement
.
Rotarymeter pressure loss curve
Pressure loss
EXAMPLES OF WORK CARRIED OUT
CUSTOMER NAME
Pegasus House
TYPE
∆P
LOSS(mbar)
G65
BRAND
FLANGE
DIAMETER
CLASS
DECSRIPTION
SCHLUMBERGER
2"
150
Wrong Installation
2
Unlubricated Meter
Özen Đşmerkezi
6.Gazetecil. sit. B
blok
Profesörler sit. B4
blok
G 100
5
DRESSER
3"
300
G 65
2.2
INSTROMET
2"
150
G65
1.8
DRESSER
2"
150
AKIN ESTATE
G 160
4.5
SCHLUMBERGER
3"
300
DRESSER
3"
300
DRESSER
3"
150
3"
150
Cabin prevents lubrication
Unlubricated Meter excessive
pressure loss
Installation error
counter/numerator against a
wall
MĐMARLAR ESTATE
G 100
4.3
Unlubricated Meter
Unlubricated Meter
Meter sloping Faulty oil plug
unable to lubricate
Carfarma
G 100
2.7
Doğuş Đnşaat
G 100
3.3
Pirelli apt.
G 65
2.5
DRESSER
2"
150
Excess lubricant level
Sezai Özderici sit.
Tel no:3519194
G 65
2.3
DRESSER
2"
150
Meter sloping .Lubricant
topped up
4.Gazetecil. sit. C2
blok
G 65
DRESSER
2"
150
Faulty installation. No filter.
DRESSER
Gazete muh.sit.
2.6
G 160
SCHLUMBERGER
3"
150
Front section oil level normal .
Back section could not be
examined due to fittings .
Faulty installation
SCHLUMBERGER
3"
150
Faulty back oil plug .Faulty
installation
2"
150
Unlubricated Meter. Sloping
installation
3"
150
Improper cabin and meter
installation. Unable to
lubricate. No seal.
3"
150
Unlubricated Meter. Sloping
installation
3"
150
Improper cabin and meter
installation. Unable to
lubricate. No seal.
5.4
Motor Jeans
G 100
4.7
INSTROMET
Crystal
Hotel
G 100
3.7
INSTROMET
Golden
Age 1
G 100
4.5
ELSTER
Kağıthane
Municipality
G 160
Soyhan Estate
G 100
7.5
Dresser
6
.
The last two meters in the list were dismantled and recalibrated. The calibration values are
given below
CONCLUSION
During the work carried out and in the subsequent calibration, it was observed that there is a relation
between calibration and loss of pressure.
The pressure losses were the values obtained during the meters maximum values. It would not seem
possible to observe such pressure losses at minimum and above levels.
It has also been observed that faulty meter installation, inadequate filtration of the gas, and the inability
to regulate the control the lubrication on a regular basis has had a detrimental effect on meter
performance
The measurement interval in the meters investigated was 1:20. For the last year meters with a
measurement interval of 1:50 or 1:60 have been used in Istanbul.
One of the conclusions that has been reached as a result of this work is that the relation between loss
of pressure and calibration and its relation to measurement interval should be further investigated
A further comparison will have to be made between the pressure loss and calibration results amongst
the meters installed in the last year. One of the conclusions that natural gas is dirty in Turkey.
Rotary meters require very little field maintenance under normal operating conditions. Periodic oil
checks ensure that the proper level is maintained and oil changed when discolored with dirt or
emulsified as a result of water. In Turkey these checks vary from one week to several years. Current
utility practices indicate that oil check are made as infrequently as six to twelve month in Turkey. The
long period is justified based upon their field experience.
REFERENCES:
[1]IGT Gas self study notes 1999.
[2] Elster rotarymeter notes
[3]Actaris gas book 2005