Note 3
Vegetable and animal oils, fats, greases and waxes are esters of polyols with fatty acids, and nearly always will contain free fatty acid.

If in contact with water at higher temperatures these esters can saponify, resulting in increased free fatty acid content. Free fatty acids, especially the short chain types, can be very aggressive to tank coatings. Thus, during loading, storage and discharge the acid values should not exceed the maximum values indicated in the table. 

 Tank Coating System Maximum acid value
(acc. to ISO 660-1996)
Approximate Percentage 
Free Fatty Acid
 Sigma PhenGuard

No Limit

up to 100 %

 Sigma NovaGuard


30 - 50 %

 SigmaGuard 720 (S'guard EHB)


6 - 10 %

 SigmaGuard 750 (S'Silguard MC)


1.5 - 2.5 %

The acid value according to ISO 660 - 1996 is the only accepted method to determine a cargo’s suitability for carriage. The Free Fatty Acid percentages given are a guide as the acid value is dependant on the molecular weight of the Fatty Acid(s).

The fatty acids (including fatty acid distillates and acid oils) accepted in this list can be transported provided they comply with the following criteria:
- the water content must be limited to 1,0 percent maximum.
- no free mineral acid content is permitted.

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