Questions We are Asked on Problem Bunker Fuels from the Houston Area


Q1 – Can we look at the ISO 8217 standard report and identify a problem fuel?

A – The only parameter from the standard analysis which will indicate the current Houston area problem fuels is TAN (Total Acid Number). Normally the TAN value is about 0.2 to 0.3 mg KOH/g (unless it is a naphthenic fuel which is quite rare). If the TAN exceeds 0.4 mg KOH/g, you should start worrying.

The problem fuels also have high RSN (Reserve Stability Number) above 9 and up to 15. Many labs do not have the facility to test for RSN but if you test and find RSN greater than 9, you should start worrying.

Q2 – Because of the problems, we have stopped buying fuels from the Houston area. Can you advise if it is safe now and from what date the bunkers in Houston are safe to buy?

A ‐ Most of the Houston supplied bunkers that caused problems were bunkered in March to Mid‐April and it took over 20 days for the problems to show up. As of now, there have been no complaints of machinery problems with fuels supplied from May 1st 2018. The TAN values are also in the normal range of 0.2 to 0.3 mg KOH/g. We are not ready to certify that Houston fuels are fine because it is still only one month from May 1st. However, you can insist on the supplier providing you a test certificate and warranty regarding these contaminants before you bunker.

Q3 – Why is it taking 20 days to 1 month for these bad fuels to start causing problems to the machinery?

A – This is an interesting question. In some of these fuels, we have carried out the same test over a period of time. We have seen that the Xylene Equivalent test value (indicative of the stability) which is in the range of 30 during initial testing is going up to 70 (more unstable) after 3‐4 weeks. Also, the RSN (Reserve Stability Number) test values which were initially around 3 to 5 (normal) are reading over 10 (more unstable) after 3‐4 weeks. On ships, the fuels are not only stored but they are also heated. What changes are taking place in the fuel during this period is not known. The tests that we conduct pertain to the fuel at the time of bunkering.

Q4 – Another testing lab is reporting that the damage is caused because of the presence of 4‐cumyl phenol. Your diagnosis seems to be different?

A – We can only comment on the fuel samples we have received and tested. In these samples, the 4‐cumyl phenol has been very low (equal to or less than 20 ppm) and at this level, this cannot be the reason for the problems in the samples received by us.

Best regards,

Dr. Vis

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