Pour Point & Cloud Point

Standard test for Pour Point: ISO 3016
Upper Pour Point (Winter): 30°C
Upper Pour Point (Summer): 30°C


For a suitable safety margin it is recommended that the heating system in tanks and transfer pipes be able to maintain the fuel minimum of 5-10°C above the Pour Point of the fuel in question, otherwise the pumpability of the fuel will be vastly reduced as wax crystals begin to precipitate with the drop in temperature as the solubility of paraffins in the hydro-carbon drops. These will accumulate and stop the flow of oil. 

Questions to ask?

  • Can the heating systems cope with the higher pour point?
  • Is there enough safety margin between minimum pumpable temperature / maximum temperature for treating and flash point?

As before if the answer to either or these questions is no than a call at the next port will be necessary to offload the product. There are pour point depressants called flow improvers which can be added to a fuel which work effectively and may avoid a port call in the first instance. However, the additives cannot prevent the crystallization but rather delay the agglomeration of the wax. Instead the crystals will tend to accumulate at the bottom of the tank and there is the added problem of potential clogging of fine filters when the temperature does drop below the start of the crystallization point known as the Cloud Point.

Standard test for Cloud Point: ISO 10478


Special distillate fuels with a lowered Cloud Point are produced with sub 0°C for vessels working in colder conditions or for emergency service vessels with external Diesel generators to allow full operation.