Petroleum Inspection and Testing in Pakistan: Quantity and Quality

Key Takeaways

• Quantity is settled by measurement: shore tank gauging, vessel ullage or innage, temperature, and correction to a standard reference condition.

• Quality is settled by analysis. The sampling regime decides whether the result describes the cargo or only a bottle.

• A spot sample answers a narrow question. A running sample and a composite answer wider ones.

• Manual sampling is set out in ASTM D4057 and automatic sampling in ASTM D4177.

• Chain of custody is evidence. A certificate of quantity and quality is what a bank examines and what a claim turns on.

Two questions on one cargo

A cargo of diesel or petrol is bought on two axes at once, and both must be satisfied: quantity is how much material left the seller and reached the buyer, and quality is whether that material meets the specification the contract names.

They fail separately. A cargo can arrive at the right volume and the wrong sulphur level. It can meet every quality parameter and still show a shortage against the bill of lading, and a trader who treats one certificate as covering both is exposed on the other.

Terminal practice reflects the split. A vessel discharging at Karachi or Port Qasim is measured before and after transfer. Samples are drawn during transfer and analysed while the ship is still alongside. The certificate of quantity and the certificate of quality follow.

Quantity: gauging the shore tank and the vessel

Quantity determination is a chain of measurements, and every link has a method.

Shore tanks are gauged by taking the liquid level, the free water level and the temperature, then applying the tank's capacity tables, which gives a volume in a tank and not yet a quantity. Vessel compartments are read from a different reference: innage is the depth of liquid from the tank bottom to the surface, and ullage is the empty space from the tank top down to the liquid surface. Both describe the same liquid. They are used together because a ship's tanks carry structure and trim. The American Petroleum Institute's Manual of Petroleum Measurement Standards covers this work, including measurement and sampling of cargoes on board tank vessels.

Temperature matters because liquids expand. Readings are taken at several levels and averaged, because a warm top layer and a cool bottom layer are common after discharge, and density comes from the laboratory, measured on a sample by hydrometer under ASTM D1298. Observed volume is corrected to a standard reference condition using the joint API and ASTM tables described in ASTM D1250, and those tables use base temperatures of 15 degrees Celsius and 60 degrees Fahrenheit.

Two residues are accounted for. On board quantity is material already in the vessel's tanks before loading, and remaining on board is what stays after discharge and cannot be pumped out; either omission is a common cause of a shortage claim with no real cause.

The independent inspector is what makes the figure acceptable to both sides, and an inspector nominated in the contract attends the gauging, draws the samples, and issues the certificate. Neither seller nor buyer reads the gauge alone.

Quality: the parameters behind the certificate

Quality determination starts with a specification. A contract for diesel, petrol, jet fuel or furnace oil names the grade and the standard that defines it.

The common grades have published specifications that group their requirements: ASTM D975 covers diesel fuel and separates its grades by sulphur level, and its required properties include flash point, water and sediment, carbon residue, ash, distillation, viscosity, copper corrosion, cetane number and lubricity. ASTM D4814 covers automotive spark-ignition fuel and varies volatility with season and locality, and ASTM D1655 covers Jet A and Jet A-1, and organises requirements as composition, volatility, fluidity, combustion, corrosion, thermal stability, contaminants and additives.

Each parameter controls a behaviour rather than one universal number. Vapour pressure, measured under ASTM D323, describes how readily a fuel evaporates, while distillation under ASTM D86 establishes the boiling range a specification uses to control volatility, and flash point under ASTM D93 gives the temperature at which vapour ignites under test conditions. Cetane number under ASTM D613 measures ignition quality in diesel, and sulphur is determined by X-ray fluorescence under ASTM D2622. Viscosity is measured under ASTM D445, and corrosiveness to copper under ASTM D130.

The test establishes the value. The specification, or the contract that repeats it, sets the limit.

Sampling: what makes a result representative

A laboratory result is only as good as the sample it describes. Sampling is where most petroleum disputes are decided.

Sample types are separated by the question they answer. ASTM D4057 sets out manual sampling of petroleum and petroleum products. It states the limitation plainly: a spot sample provides material from one particular point in a tank, vessel compartment or pipeline, and a running or all-level sample represents only the column of material it was taken from. Tank sampling for quality therefore draws from the upper, middle and lower levels. A representative composite combines them in proportion to the volume each level represents.

A running sample is drawn continuously from a flowing stream across the whole transfer, so the container accumulates a record of the cargo as it moved rather than a snapshot of one moment. Automatic systems do the same job mechanically and proportionally to flow; ASTM D4177 describes their design, siting and proving, and states the purpose directly: representative samples are required to establish standard volumes, prices, and compliance with commercial terms.

Composite sampling reduces the bottles to one sample that represents the parcel. How the composite is built, and in what proportions, belongs in the record. Two composites from one cargo can give different numbers if they were not built the same way.

Chain of custody is the weakest link in most files. A sample has to be traceable to the tank, the time, the method and the person who drew it, and it has to stay sealed and identifiable until it is tested. TTI maintains secure chain-of-custody controls from receipt to report.

What the certificate does commercially

The certificate of quantity and quality is not a formality. Payment and claims both run on it.

For payment, it is usually one of the documents a buyer's bank examines under a documentary credit, and the Uniform Customs and Practice for Documentary Credits, published by the International Chamber of Commerce as UCP 600, governs letter of credit transactions worldwide. The terms of the credit decide which documents must be presented and what they must show. A certificate that does not match the credit's wording is a discrepancy, and a discrepancy delays payment even when the cargo is sound.

For claims, the same certificate supplies the number. A shortage claim compares the quantity on the bill of lading with the quantity that came out at the discharge port, less any transit loss the contract allows. A demurrage claim is a different claim on a different record: it concerns time lost beyond the laytime the charter party allows, and it rests on the statement of facts rather than on the laboratory. Both are argued with documents, and the independent certificate is the one both sides accepted in advance.

Reading a Pakistani petroleum report

Three checks catch most problems in a petroleum test report.

Confirm that the accreditation scope behind the method covers the parameter tested. TTI Testing Laboratories holds PNAC accreditation LAB-022, published as a scope document, and operates an OGRA approved petroleum and lubricants testing laboratory; OGRA is the Oil and Gas Regulatory Authority, whose mandate covers petroleum products and lubricants. Confirm that the sample identification on the report matches the tank and the transfer, and that the method named, including its edition, is the one the specification requires.

TTI's petroleum testing laboratory covers fuels and distillates, lubricants and greases, transformer oil, base oils and heavy fuels, and oil condition monitoring. Its scope document is PNAC LAB-022.

Where the question is adulteration rather than specification compliance, the panel changes: density, distillation and flash point are read together, because blending kerosene into diesel moves several properties at once.

FAQ

What is the difference between a certificate of quantity and a certificate of quality? A certificate of quantity states how much product was measured, usually from shore tank gauges checked against vessel figures, and a certificate of quality states what the product is, from laboratory analysis of a sample.

How is the quantity of a petroleum cargo measured? By gauging shore tanks and vessel compartments, taking temperatures and densities, and correcting observed volumes to a standard reference condition. On board quantity and remaining on board are accounted for.

Why does sampling decide the result of a petroleum test? Because a sample that does not represent the parcel describes only the container. A spot sample covers one point. A running or all-level sample covers a column. The regime has to match the question asked.

Which specifications apply to diesel and petrol? Diesel grades are commonly defined by ASTM D975, which separates grades by sulphur level, and petrol by ASTM D4814, which varies volatility with season and locality. The contract decides which edition applies.

Can a test report decide a demurrage claim? No. Demurrage concerns time lost beyond the allowed laytime and rests on the statement of facts. A test report answers quality and condition questions instead.

Conclusion

• Quantity and quality are separate determinations. A cargo is settled only when both are certified.

• Quantity rests on measurement, temperature and density correction, and a full account of residues.

• Quality rests on a sample. The sampling regime is what gives the result meaning.

• Chain of custody decides whether a result can be used in a dispute.

Book petroleum testing with TTI Testing Laboratories. UAN 111 786 001. ISO/IEC 17025 accredited, PNAC LAB-022.

References

1. Petroleum testing services, TTI Testing Laboratories, https://ttilabs.net/petroleum

2. Accreditation and approvals, TTI Testing Laboratories, https://ttilabs.net/accreditations/

3. Analytical testing services, TTI Testing Laboratories, https://ttilabs.net/testing

4. Contact, TTI Testing Laboratories, https://ttilabs.net/contact

5. Accreditation scope LAB-022, Pakistan National Accreditation Council, https://pnac.gov.pk/pdfFiles/LAB-022

6. ASTM D4057-19, Standard practice for manual sampling of petroleum and petroleum products, ASTM International, https://www.astm.org/d4057-19.html

7. ASTM D4177-22, Standard practice for automatic sampling of petroleum and petroleum products, ASTM International, https://www.astm.org/d4177-22.html

8. ASTM D1298-12b(2017), Standard test method for density, relative density, or API gravity of crude petroleum and liquid petroleum products by hydrometer method, ASTM International, https://www.astm.org/d1298-12br17.html

9. ASTM D1250-19, Standard guide for the use of the joint API and ASTM adjunct for temperature and pressure volume correction factors (API MPMS Chapter 11.1), ASTM International, https://www.astm.org/d1250-19.html

10. Petroleum measurement catalogue, American Petroleum Institute, https://www.api.org/-/media/files/publications/2024-catalog/2024-petroleum-measurement.pdf

11. ASTM D86-23, Standard test method for distillation of petroleum products and liquid fuels at atmospheric pressure, ASTM International, https://www.astm.org/d0086-23.html

12. ASTM D93-20, Standard test methods for flash point by Pensky-Martens closed cup tester, ASTM International, https://www.astm.org/d0093-20.html

13. ASTM D323-20a, Standard test method for vapor pressure of petroleum products (Reid method), ASTM International, https://www.astm.org/d0323-20a.html

14. ASTM D613-23, Standard test method for cetane number of diesel fuel oil, ASTM International, https://www.astm.org/d0613-23.html

15. ASTM D2622-21, Standard test method for sulfur in petroleum products by wavelength dispersive X-ray fluorescence spectrometry, ASTM International, https://www.astm.org/d2622-21.html

16. ASTM D445-19, Standard test method for kinematic viscosity of transparent and opaque liquids, ASTM International, https://www.astm.org/d0445-19.html

17. ASTM D130-18, Standard test method for corrosiveness to copper from petroleum products by copper strip test, ASTM International, https://www.astm.org/d0130-18.html

18. ASTM D975-24, Standard specification for diesel fuel, ASTM International, https://www.astm.org/d0975-24.html

19. ASTM D4814-23a, Standard specification for automotive spark-ignition engine fuel, ASTM International, https://www.astm.org/d4814-23a.html

20. ASTM D1655-24a, Standard specification for aviation turbine fuels, ASTM International, https://www.astm.org/d1655-24a.html

21. Uniform rules for documentary credits (UCP 600), ICC Academy, International Chamber of Commerce, https://academy.iccwbo.org/trade-finance/e-books/UCP-600/

22. Oil and Gas Regulatory Authority, Government of Pakistan, https://ogra.org.pk/