Petroleum Inspection and Testing in Pakistan: Quantity and Quality

Quantity and quality are separate certificates

A trader who treats one certificate as covering both is exposed on the other. A vessel discharging at Karachi or Port Qasim is measured before and after transfer, samples are drawn during transfer and analysed, and the certificate of quantity and the certificate of quality follow.

How quantity is measured

Shore tanks are gauged for liquid level, free water level and temperature, and the tank's capacity tables turn those readings into a volume. Vessel compartments are read differently. Innage is the depth of liquid from the tank bottom to the surface; ullage is the empty space from the tank top down to the surface. Both describe the same liquid, and 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 on tank vessels.

From gauge to certificate, a quantity is built in five steps:

• Gauge: liquid level, free water and temperature in shore tanks; ullage or innage on board. Temperature is read at several levels and averaged, because layers differ.

• Volume: capacity tables turn the readings into an observed volume.

• Density: measured on a sample by hydrometer under ASTM D1298.

• Correct: to the standard condition with the joint API and ASTM tables in ASTM D1250, which use base temperatures of 15 °C and 60 °F.

• Certify: the independent inspector, named in the contract, issues the certificate.

Two residues must be accounted for. On board quantity is material already in the vessel's tanks before loading; remaining on board is what cannot be pumped out after discharge. Leaving either out produces a shortage on paper that never happened.

Worked example: why small errors become tonnes

Take a parcel of 30,000 m³ of diesel at standard condition (illustrative figures). Mass is volume × density:

• At 835 kg/m³: 30,000 × 835 = 25,050,000 kg, or 25,050 t.

• At 837 kg/m³: 30,000 × 837 = 25,110,000 kg, or 25,110 t.

• A density difference of 2 kg/m³, 0.835 against 0.837 in g/mL, moves the cargo by 60 t.

A shortage claim works the same way. If the bill of lading shows 25,050 t and the outturn is 24,930 t, the difference is 120 t, or 0.48%. Whether that is a claim depends on the transit loss the contract allows, and on whether on board quantity and remaining on board were deducted on both sides.

How quality is tested

The contract names the grade and the standard that defines it. ASTM D975 covers diesel and separates its grades by sulphur level. ASTM D4814 covers automotive spark-ignition fuel and varies volatility with season and locality. ASTM D1655 covers Jet A and Jet A-1.

The test gives the value; the specification, or the contract that repeats it, sets the limit. When the question is adulteration, density, distillation and flash point are read together, because blending kerosene into diesel moves several properties at once.

Pakistan's limit: Euro-V and 10 ppm sulphur

In Jul 2020 the Petroleum Division's Directorate General of Oil notified Euro-V specifications for all three petrol grades (RON 92, 95 and 97) and barred imports of petrol below Euro-V from 1 Aug 2020 and diesel below Euro-V from 1 Jan 2021, with sulphur limited to 10 ppm, as Dawn reported. OGRA and the Hydrocarbon Development Institute of Pakistan were asked to implement them. Two years earlier, Pakistan's diesel imports were Euro-II at 500 ppm (Dawn, Sep 2018).

A 10 ppm limit changes what the laboratory has to prove. ASTM D2622 (wavelength dispersive XRF) states a pooled limit of quantitation of 3 mg/kg and says precision does not apply below it, and that a specific laboratory's quantitation limit depends on its instrument and practices. So for a result near 10 ppm, ask the laboratory for its own quantitation limit and the measurement uncertainty before reading pass or fail.

Sampling decides whether a result describes the cargo

Most petroleum disputes are decided at sampling. ASTM D4057 sets out manual sampling and states the limitation plainly: a spot sample represents one point in a tank, compartment or pipeline, and a running or all-level sample represents only the column it was taken from. Tank sampling for quality therefore draws from the upper, middle and lower levels, and a composite combines them in proportion to volume.

Automatic samplers draw in proportion to flow across the whole transfer. ASTM D4177 covers their design, siting and proving, and says representative samples are required to establish standard volumes, prices and compliance with commercial terms. How a composite was built belongs in the record, because two composites from one cargo can give different numbers.

Chain of custody decides whether a result can be used in a dispute. Each sample must be traceable to the tank, time, method and person who drew it, and stay sealed until tested.

Payment and claims run on the certificate

For payment, the certificate is usually one of the documents a bank examines under a documentary credit governed by the International Chamber of Commerce's UCP 600. The credit decides 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 bill of lading quantity with the outturn, less any transit loss the contract allows. Demurrage is a different claim: time lost beyond the laytime in the charter party, argued from the statement of facts, not from the laboratory.

Checklist before accepting a certificate

• The method named for each parameter, with its edition, is the one the contract specification requires.

• The laboratory's accreditation scope covers that method and product. Check the scope document, not the logo.

• Sample identification on the report matches the tank, compartment and transfer.

• The sample type is stated: spot, all-level, running or composite, and how the composite was built.

• On board quantity and remaining on board are shown on the quantity certificate.

• Results near a limit show the quantitation limit and measurement uncertainty.

• The certificate wording matches the documentary credit before it goes to the bank.

What Tti Labs' petroleum laboratory covers

• Petroleum testing of fuels and distillates (gasoline, diesel, kerosene, LDO, jet fuel, furnace oil and coal), lubricants and greases, transformer oil, base oils and heavy fuels.

• ISO/IEC 17025 accreditation under PNAC LAB-022. Its petroleum section lists flash and fire point (ASTM D92, D93), kinematic viscosity (D445), viscosity index (D2270), colour (D1500), density (D1298), total acid number (D974) and total base number (D2896). Ask whether any other method will be reported under accreditation.

• An OGRA approved third-party quality laboratory for petroleum products and lubricants. OGRA is the Oil and Gas Regulatory Authority.

• Chain-of-custody controls from receipt to report, through analytical testing services.

Tti Labs tests samples. Tank and vessel gauging is the cargo inspector's work, and the inspector named in the contract issues the quantity certificate.

Book petroleum testing with Tti Labs. UAN 111 786 001. ISO/IEC 17025 accredited, PNAC LAB-022.

Related guides: Third-Party Inspection in Pakistan: How Independent QC Actually Works, Lab Testing for Pakistan Exports: What Buyers Need to Verify.