PETROLEUM PRODUCTS MEASUREMENT AND
QUALITY ASSURANCE.
PAPER PRESENTED AT THE NATIONAL
SEMINAR ON PETROLEUM MEASUREMENT.
1987.
BY
ENGR. E. A. AGBOLA.
ABSTRACT.
The Petroleum Inspectorate is charged with the responsibility of monitoring
the operations of the Petroleum/Petrochemical processing plants and the
activities of the Petroleum products Marketing Companies to ensure they
operate in accordance with requirements of the Petroleum Regulations.
Petroleum Products manufactured from the three Refineries in Kaduna,
Warri, and Port Harcourt are distributed through a network of Pipelines to
Depots located strategically all over Nigeria. Imported products from
offshore operations arrangement are received at the Apapa, Atlas Cove,
Warri, and Port Harcourt Jetties. Petroleum Products are evacuated from the
depots by road tankers to various Petrol Stations and other retail Outlets.
The paper presents methods and modes of measurement of Petroleum
Products, and highlights the role of the petroleum Inspectorate in ensuring
that products are manufactured to specification standard, that products are
accounted for at the processing plants, bulk storage depots and retail outlets,
and that these products are distributed to consumers on specification.
PREAMBLE.
In the Petroleum Industry, Crude Oil and the products from it exist generally
in liquid or gaseous forms. Accurate measurement of the Crude Oil and the
Products, which are bulk fluids, is of prime importance, such accuracy
obviates disputes about receipts into terminal storage and on deliveries to
customers, while promptly alerts operators to unnecessary products losses.
Large volumes of Refinery/Petrochemical Products are manufactured at a
time and transferred into storage tanks within the plants as either
intermediate or finished products. Both are transferred from plant storage
either for further processing or by Sea, Rail, Road, or Pipeline to end users.
It therefore becomes important to monitor and establish the quantities
transferred.
The different modes of transfer and storage suggest various ways and means
of measuring the volumes of fluids under movement. In the process of
measurement certain parameters especially Temperature, Densities/Specific
Gravities play such important roles, that tables that are concerned with the
effect of temperature on volumes, specific gravities or densities, for
example, have been complied jointly by the American Society for Testing
Materials (ASTM) and Institute of Petroleum (IP) of United Kingdom.
It is of great importance to maintain the quality of products throughout
various phases of the distribution network from the Refinery to consumers.
The Refineries manufacture Petroleum Products to specification standards
approved by the Standard Organization of Nigeria. The Oil marketing
companies also have established procedures for handling various grades of
Petroleum Products to prevent contamination with other grades, water or
sediments. The petroleum Inspectorate therefore monitors the operations of
the Refineries to ensure that products manufactured meet specification
standards and are accurately accounted for through joint participation in all
stock taking exercise.
The petroleum Inspectorate also monitors shipment of these products by Sea,
Rail, Road and network of Pipeline to bulk Storage Deposits. The activities
of the oil marketing companies are monitored to ensure correct volume of
products are sold at approve prices and that products sold meet specification
standards.
CALIBRATION.
To measure a quantity of oil, it is first necessary to have an accurately
calibrated measuring device which may be storage tank, a barge or ship, a
road or rail vehicle, or a metering instrument.
TANK CALIBRATION.
Storage tanks and ships tanks are generally calibrated by mathematical
calculation based on the dimensions of the tanks: this is known as the
strapping method. The necessity of accurate tank calibration becomes
particularly evident where tanks are used for stock control or custody
transfer measurement. The best gauging system is useless if it is based on
doubtful calibration tables.
FACTORS AFFECTING VOLUME MEASUREMENT
The following factors which influence the ratio between liquid level and
volume are taken into account when calibrating tanks:- The physical dimensions must be measured with properly calibrated
instruments.
- Environmental factors must be taken into account, such as
Temperature corrections, Wind forces, and Rainfall.
- Random errors, due to human faults, in calibration must be
minimized, such as tape sagging, variations to incorrect pull and
sloppy leveling of instruments.
- The calibration table must be related very accurately to the gauging
datum point.
Any movement of this point due to tank wall or bottom deformations must
be avoided by the tank builder and operator. Road tankers are calibrated by
gradual filling from containers of known capacity. As each compartment is
filled, a rod known as dip stick is marked with the corresponding levels at
intermittent points.
Calibration of tanks for storing Petroleum Products are normally carried out
by companies approved and duly registered by the Petroleum Inspectorate.
Representatives are present to witness the calibration exercise. At the end of
the exercise, the calibration tables are made available to us.
MEASUREMENT IN BULK STORAGE TANKS.
Tank dipping is the method used in the measurement of the level of Oil in
tank with the approved steel tape. This tape is graduated with reversed
numeral on the inside for easy reading.
A Plump bob mounted on a swivel is attached to the end of the tape, so as to
maintain the whole length in tension when fully immersed in a liquid. The
step by step procedure for tank dipping is as follows:  Ensure that the liquid surface in the tank is free of foam and waves
due to agitation.
 Inspect the tape to ensure that it is free of kink and graduations are
clearly visible.
 With the smooth (ungraduated) side of the tape in contact with the rim
of the gauging hatch at the reference point gradually lower the bob
and tape into the tank until the plumb bob gently touches the datum
plate in the tank. Ensure that the tape is not lowered too far, as the bob
will tilt and an incorrect gauge will be obtained.
Record the tape reading at the reference point and note any variance
from the reference depth. It is essential to avoid either sagging of the
tape or its deviation from the vertical plane as this could introduce
appreciable errors.
 Withdraw the tape quickly, read and record the liquid cut on the tape
as the innage in case of black Oil tanks.
 In case of white Product tanks, visually determine the approximate
product level at which to apply the Oil finding past. Carefully clean
the tape and evenly apply the Oil finding paste over a distance of 6ins
(152mm) around this approximate liquid cut point.
 Gently repeat the last two steps above and record the accurate tape
reading at the liquid cut point. This gives the innage.
 All records must be entered into the note book provided.
SAMPLING
Sampling incorporates all steps required to obtain a representative quantity
of the content of any Pipe, Tank or other system for quality determination.
For a sample to be of value, it should meet the following conditions: - It must be reproducible
- It must be unpolluted
- The sample must be properly labeled
- .The sample must be properly stoppered
- Where samples are required at more than one level in a tank,
The order of sampling should be from top downwards, so that each sample
will be obtained before the liquid at that level is disturbed.
- Sampling should be conducted immediately after dipping the tank.
- The sampling apparatus including the cord should be clean and free
of any contaminated and the “thief can” should be thoroughly rinsed
with the liquid being sampled before it is lowered into the tank to
withdraw the sample.
The sampling apparatus shall be the “thief can”. All tanks must be sampled
during daily, monthly and yearly stock taking and during Fiscalisation. The
step by step sampling procedure is as follows:i.
The operator shall inform all parties involved about the tanks to be
sampled at least one hour before the start of sampling.
ii.
At the designated time the parties ascend the tank for the sampling
exercise. The sampling technician ascends the tanks with sampling
bottles, labeling material, dipping tape, water and oil finding paste
and thermometer.
iii. The operator /gauge establish the liquid level of the tank in order to
Know how many samples are required and at which levels they are
to be taken.
iv. Lower “thief can” to the desired level; open the can by gently
jerking the cord to allow oil to flow in.
v.
Gently withdraw the “thief can” to the surface for temperature
measurement.
COMPUTATION OF QUANTITY OF PRODUCT IN
STORAGE TANK
To do this, a sample is taken and is allowed to attain ambient temperature.
After determining product volume in tank, its density must be determined.
The thermometer and hydrometer immersed in the 500ml glass cylinder
measure the temperature and the specific gravity respectively.
COMPUTATION OF QUANTITY OF PRODUCT
i.
The tank dip is referred to the appropriate Tank calibration chart to
obtain the apparent/ gross volume of product.
ii.
The observed density of the.product at the observed temperature is
converted to density at 150c using ASTM Table 53B.
iii.
The volume correction factor is obtained using corrected at 150c
from ASTN Table 54B.
iv.
Multiply the Apparent / Gross Volume (i) by the volume correction
factor (iii) to obtain the corrected volume of product in cubic meters
(M.3).
v.
Multiply the corrected volume M.3 by the corrected density to
obtain the quantity of product in metric tons.
For floating roof tanks, obtain roof displacement using relationship
W/T = Displacement. W is the weight of the roof and T is the S>G> of
product at tank temperature. Subtract the roof displacement from the
apparent/gross volume of the product at tank temperature corrected for roof
displacement.
The Petroleum inspectorate participated in petroleum products measurement
at all custody transfer points
OCEAN/ROAD TANKER.
Calibration certificates are request by ocean and road tanker operators before
loading of petroleum products. These certificates confirm the exact volume
of the tankers, notwithstanding the provision of meters to measure same.
LOADING METERS AT DEPOTS.
Loading arms for products at depots have flow meters whose accuracies are
periodically checked by meter providing methods. There are generally two
types of provers: - Volumetric and Gravimetric, but the procedure is based
essentially on the measurement of a quality of liquid delivered by a meter
into a container of known volumes, or in which the content can be weighed
or of that delivered by a previously proved meter. Proving systems entirely
closed to the atmosphere are essential for liquid of high vapour pressure. On
the other hand open provers, with or without evaporation control, may used
for liquids with low vapour pressures.
The Petroleum Inspectorates ensures that provers are provided in all depots
and all procedures for meter proving (volumetric) is carefully followed. The
compulsory meter proving exercise for all meters in the depots is witnessed
every month by representatives of the petroleum Inspectorate. A typical
volumetric prover is cylindrical in shape and is usually 2500 liters in
capacity. It is mounted on wheels and provided externally with a gauge to
read off the volume delivered. The proof is run by loading product through
the meter until the set stop counter stops at zero.
The Prover reading and meter reading are compared. A successful run
occurs when there is no difference. If the readings are not the same the seal
to the calibrator will be broken and the calibrator is adjusted as required (i.e.
either short loading or overloading). The proving exercise is then repeated
until prover’s reading corresponds with the quantity loaded. At the end of
the exercise, the results are recorded on the meter proving sheet which must
be signed by Inspectorate representative and operator’s staff.
DISPENSING PUMPS AT PETROL FILLING STATION.
The Petroleum Inspectorate also monitors operations at Petrol Stations to
ensure that accurate volumes of Petroleum Products are sold at correct
prices. To achieve this, periodic proving of meters in dispensing Pumps are
carried out using the 10 – litre Seraphin Cans. The product is delivered into
the can, while the gauge on the cylinder is used to determine if the supply is
up to standard measure.
As a result of incessant complaints by consumers of widespread cases of
cheating in Petrol Stations through manipulation of dispensing meters, the
Petroleum Inspectorate decided to print volume/price tables which were
distributed to Oil Marketing Companies for mandatory Display on all Petrol
Stations. This is to serve as a guide to consumers for a quick reconciliation
of the amount paid with volume dispends.
This has helped consumers all over the country tremendously, and it has
helped Petroleum Inspectorate to control the activities of the unscrupulous
dealers and attendants. These volume/price tables are found in all licensed
Petrol Stations.
QUALITY ASSURANCE.
One of the tasks performed by the Petroleum Inspectorate is monitoring of
Quality of Products in the oil Industry. This task spans the entire spectrum of
the industry from Crude Production through the process plants down to
storage depots Petrol Filling Stations. The various procedures employed are
as follows:
1. MONITORING OF QUALITY OF PETROLEUM PRODUCTS AT
REFINERIES.
The Refineries operations are designed so that the desired quality is
materialized through all the processes starting from Crude intake to Products
Shipment. Products are manufactured to specification standards approved by
the standard organization of Nigeria. Each Refinery has well equipped
laboratory where appropriate tests are carried out on the Products and test
certificates issued. These test certificates are vetted by the Petroleum
Inspectorate to ensure the Products meet the set standard before shipment by
Rail, Road, Sea, and Pipeline. Products sample are withdrawn at random for
independent analysis.
2. MONITORING OF QUALITY OF PETROLEUM PRODUCTS AT
DEPOTS/JETTIES.
Petroleum products are shipped from Refineries to Depots through a
network of Pipelines. After certifying that the Products manufactured by the
Refineries meet standard specification, It is also the duty of the Petroleum
Inspectorate to ensure that the Pipeline Operators handle the shipment
carefully to prevent Product Contamination. Therefore, the operations of the
Depots are carefully monitored. Samples of products received are withdrawn
periodically for independent analysis. We also check records of laboratory
tests performed on product received in to the Depots.
At the Jetties where coastal vessel discharge products, our representatives
are permanently there. We take samples of products from the vessels and
shore tanks and carry out independent analysis before sales of the products
to the consumers.
3. MONITORING OF QUALITY OF PRODUCTS AT PETROL
STATIONS.
The Petrol Station is the final point where the Petroleum Products get to the
consumers. These Products are transported to these Petrol Stations through
road tankers. The main source of contamination of Petroleum products
identified before products get to consumers is deliberate adulteration by road
tanker drivers/dealers.
Road tanker drivers/dealers adulterate petroleum products so as to make
maximum profit. As a result of huge price differential between the super
petrol (39.5 kobo per litre) kerosene 11 kobo per litre, and Automotive gas
oil (29.5 kobo per litre) unscrupulous drivers/dealers engaged in operating
illegal depots where these products are blended. These products eventually
find their way into petrol stations where they are sold to innocent consumers.
This has reached such alarming dimension that the Nigerian National
petroleum corporation had to spend huge sum of money to lunch a publicity
campaign against it. This has also posed a serious challenge to the
management of the petroleum Inspectorate.
In view of this unpatriotic act, the petroleum Inspectorate stepped up routine
inspections of all petrol stations. Samples of petroleum products are
withdrawn for laboratory analysis. The frequent presence of the Inspectorate
representative at these petrol stations at least serves as a deterrent to the
petrol station dealers. A few cases of deliverate product adulterations have
been investigated and license of such dealer revoked.
The efforts of the Petroleum Inspectorate are complemented by those of the
Military Task Force. Some illegal depots used for blending adulterated
products were discovered by the Military Task Force. Guilty dealers have
their licenses revoked, and the stations sealed up.
THE ROLE OF PETROLEUM INSPECTORATE
In order to perform its statutory role on the operations of the
petroleum/petrochemical processing plants and petroleum marketing
companies, the petroleum Inspectorate is armed with the following
regulations : - Petroleum Refining Regulations 1974, Petroleum Regulation
1967,
Petroleum safety Regulation 1969 and Petroleum (Amendment)
Decree No 33 of 1977. The Regulations empower the petroleum Inspectorate
to carry out the following functions before any facility for processing,
storage and sales of petroleum products are operated.
 Obtain detailed drawings of the facilities with detailed write- up on
the proposal.
 Carry out the inspection of the site for the construction of the
proposed facilities/plant.
 Grant approval for the construction of the facilities/plants if
necessary conditions are met.
 Carry out of pre- commissioning inspection of the facilities/plants.
 Issue license for the facilities/plants to operate if necessary
conditions are met.
 Carry out periodic inspection of the facilities/plants.
 Renewal of operating licenses annually.
The following are the existing Facilities/Plants monitored by the Petroleum
Inspectorate (see Appendix 2and 3)
 Refineries.
 Petrol-Chemical Plant.
 Lubricating Plants.
 LPG Refilling Plants.
 Petrol Filling Stations.
 Bulk Storage Depots.
In order to monitor the Processing and Marketing operations effectively, the
Petroleum Inspectorate operates from three zonal offices at Kaduna, Port
Harcourt, and Warri, with the headquarter in Lagos. The headquarter collates
the returns on Production and Consumption from the Refineries and Oil
marketing companies respectively and reconcile these figures with those
collected independently by our field officers.
The Petroleum Inspectorate recently opened area offices in Sokoto, Markudi,
Ilorin, and Mosimi. More area offices will be opened in Ibadan, Jos, and
Enugu to bring our Services nearer to our customers. Arrangements are
already concluded to have our representatives in all the Depots to be able to
monitor their operations effectively.
Our laboratories at Warri, Kaduna, and Port Harcourt are being upgrade to
enable us expand our testing programme. The Petroleum Inspectorate is
planning to build a national laboratory which will equip for quality control.
These are the efforts the Petroleum Inspectorate is making to ensure
consumers of Petroleum Products all over Nigeria derive maximum
satisfaction from their money. We also have intensified training and
retraining of our technical staff to be able to cope with the challenging
opportunities in the area of Petroleum measurements and quality assurance.
CONCLUSION.
The Petroleum Inspectorate will continue to intensify its efforts in ensuring
Oil industry is effectively monitored. However, we will appeal to various
Marketing Companies, both majors and independents to supervise their
dealers through periodic visits to endure that fraudulent activities are
reduced to bearest minimum and eliminated eventually. They should also
educate their dealers on the danger posed by product adulteration. It is
nevertheless recognized that the greatest quality assurance effort and
opportunity lie in adequate process control and careful handling of products,
during manufacturing and transportation to Depots. Therefore the Petroleum
Inspectorate will invoke all the provisions in the Petroleum Regulations in
closely monitoring the performance of the process plants and the operations
in all depots