Inspection and verification

LPG Quantity Surveys, Sampling and Quality Testing

2015-12-26 04:20:13 | Lượt xem: 2057 | Inspection and verification

How LPG quantity is determined on vessels and in shore tanks, how samples are taken, and how quality tests are selected to meet delivery requirements.

Đọc bài viết bằng tiếng Việt →

ITVC supports customers involved in the production, distribution and storage of liquefied petroleum gas (LPG). The scope may include quantity determination, sampling and quality testing during storage, delivery and custody transfer.

1. Determine the LPG quantity

On board vessels: check the required documents, trim/list, liquid LPG level, temperature and pressure in each tank. Level readings must use the measurement system and procedure approved for the equipment, including a sliptube where appropriate. Calculate liquid-phase and vapour-phase LPG separately and repeat the measurements before and after loading or discharge.

In shore tanks: check liquid level, temperature and pressure; determine the LPG mass in both liquid and vapour phases using the tank documentation, product properties and agreed calculation method.

Mass delivered from a tank = Mass before delivery − Mass after delivery
Mass received into a tank = Mass after receipt − Mass before receipt

Account for any other transfers during the delivery or receipt period. Whether the operation is a receipt or delivery determines the direction of subtraction; do not use the same direction for both.

2. LPG sampling

The original article refers to ASTM D1265-11 for manual sampling of liquefied petroleum gases. Before carrying out the work, agree the applicable standard edition, sampling cylinder, storage conditions and test requirements. LPG sampling must be performed by competent personnel following an approved safety procedure.

3. Quality testing parameters

The following list helps identify the required tests. Confirm the standard edition and testing scope for each request.

Parameter	Reference method
Vapour pressure at 37.8°C	ASTM D1267; ASTM D2598 when calculated from composition
Hydrocarbon composition: methane, ethane, propane, propene, iso-butane, n-butane, butene and pentane	ASTM D2163
Density at 15°C	ASTM D1657; ASTM D2598 when calculated from composition
Total sulphur	ASTM D2784; other methods as agreed and within their applicable scope
Copper strip corrosion at 37.8°C for one hour	ASTM D1838
Free water	Observation according to the applicable procedure
Residue after evaporation	ASTM D2158
Volatility / temperature at 95% volume evaporation	ASTM D1837
Hydrogen sulphide (H₂S)	ASTM D2420; other methods within their applicable scope
Molecular mass	Calculated from composition
C3/C4 ratio	Calculated from composition

If arsenic or another contract-specific parameter must be tested, identify a suitable test method; do not report arsenic results using ASTM D2158.

Check the standards' scope: ASTM petroleum standards collection and ASTM D1837 — LPG volatility.

4. Information to provide when requesting a service

LPG type, loading/discharge or storage location, vessel/tank identification and expected timing.
Survey purpose: quantity verification, sampling, quality testing or a combination.
The parameters, methods and quality limits specified in the contract.
Reporting and sample retention requirements, and the parties attending as witnesses.

ITVC GLOBAL · SERVICE ENQUIRIES