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.