Comparing Test Results with Limit Values

Fuel should be ordered and delivered to a product quality standard. ISO 8217 is a typical example of such a standard and is the most significant in the marine industry. Ordering by viscosity or generic trade name is still often used, the full specification of the fuel is incomplete and limits may be applied in an arbitrary fashion. This practice can be much improved by the use of proper standards and tools for interpretation. 

The analyses presented here deal with the ISO 8217:2010 specification and the rules of interpretation.



When the reported test results exceed the specification limit, there is often a judgement made, without an understanding of the limitations of the testing, that the fuel is out of specification. Frequently, the claim is unwarranted and the fuel is on spec despite the apparently anomalous test result. 



There are at least two significant limitations to the testing of residual fuels - the test method used and the equipment/laboratory itself. As in any measurement, all tests are subject to tolerance factors. The allowable tolerance in a test or technique is referred to as the "statement of precision" and some tests are significantly less accurate than others. In recognition of this, ISO 8217:2010 states:



The test methods specified in Tables 1 and 2 [marine distillate and residual fuels] all contain a statement of precision (repeatability and reproducibility), [except for CCAI which is contained in ISO 8217]

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ISO 4259:2006, which covers the use of precision data in the interpretation of test results, shall be used in cases of dispute. [The relevant clauses of ISO 4259 are 9 and 10]

The Process:

1.    Value specified - on ordering
2.    Value tested - on delivery
3.    Precision data - apply test results
4.    What can be used?
5.    Debunker if all else fails

It should be noted that MARPOL Annex VI contains a specific procedure for the verification of fuel sulphur content using ISO 8754 test method (Petroleum products -- Determination of sulfur content -- Energy-dispersive X-ray fluorescence spectrometry) and states

“The results obtained from the verification procedure are final”