Sampling & Testing Cargoes Blended On Board Marine Vessels

IFIA AC member companies are often assigned to inspect cargoes of petroleum that are blended on
board marine vessels at the loading port with the intention to meet certain contractual quality specifications of buyers and sellers. These cargoes are usually blended from two or more shore tanks, each containing a different component. The target composition of the final blend is typically based on a composite of shore tank samples, proportionally blended in a loading port laboratory. Shippers and receivers then rely on agitation of the cargo during proportional transfer into each of the vessel’s tanks to mix all of the components to contract quality specifications.
IFIA AC members’ experience has consistently indicated that, for many physical reasons, thorough
mixing of these components does not always occur as intended. Therefore, when the blended cargo
reaches the discharge port, manual samples taken from the vessel do not yield the same test results that were obtained at the loading port.

The American Petroleum Institute (API), in its Manual of Petroleum Measurement Standards (MPMS),
has recognized the difficulties of obtaining representative samples from cargoes that are not uniform throughout their profile and cross-section in a tank. API MPMS Chapter 8.1.8.3.3.1 states that “A running/all-levels sample is not necessarily representative (because of the difficulties of ensuring proportional filling of the sampler).” API MPMS Chapter 17.1.9.7 Note: states that “...on blended cargoes, vessel tank samples often will not be representative of proportional hand-blended samples that were tested at the port of loading.”
All work performed by IFIA AC member companies is subject to regulatory audit for conformance to
industry standards. Therefore, consistent with API and ASTM standards, IFIA AC member companies
have resolved to take the following position:
1. All manual samples, shore tank and vessel tank, will be taken in accordance with methods
prescribed in API MPMS, Chapter 8.1;
2. Laboratory analysis of all samples will be performed using standard industry test procedures,
usually as specified by the American Society for Testing and Materials (ASTM);
3. If analysis results indicate a possible problem with a cargo, blending, sampling and testing procedures will be carefully reviewed and findings promptly reported to the customer(s);
4. Test method precision limits (repeatability and reproducibility) will not be used to adjust the analysis results of any sample except as specifically authorized in ASTM method D3244.

CARGO RETENTION CLAUSES.

Cargo retention clauses provide a means for interested parties to account for the quantity of cargo
remaining in a vessel’s tank/s when discharge is concluded. This quantity is reported as ROB


[Remaining on Board] on completion of discharge.
Such clauses may require the inspector conducting the ROB inspection to offer, in addition to a record
of volume, a description to be applied to the ROB material.
In accordance with internationally accepted petroleum measurement documents produced by
API/ISO/EI (previously IP), the only standard terms which IFIA member companies are prepared to
use when describing ROB are “liquid”, “non-liquid” or “free water”. The use of any other terms for the characterization of ROB material, would be subject to a written definition agreed to in writing prior to the transaction, by all interested parties.
The requirement to operate under closed or restricted conditions is becoming more common and
under these conditions it is not possible to carry out direct visual examination of retained volumes in cargo tanks. This impairs the ability of the Inspector to describe the nature of any ROB, as the assessment is limited to small amounts of material which may be retrieved via vapour lock valves.
Where a description is made, particularly under these conditions, it may not necessarily be
representative of the total volume of ROB.
Irrespective of the operating conditions, when the terms, liquid, non-liquid and free water are used by Inspectors to describe ROB, it should be noted that they apply only:

1. To the material observed by the inspector
2. At the time of measurement
3. To the material at the point of measurement


ROB - Quantity remaining on board
Sum of liquid volume, including free water and non-liquid volume in cargo tanks just after discharge has been completed, excluding clingage, hydrocarbon vapours and the contents of associated lines and pump