Orimulsion is the trade name of a relatively cheap fuel extracted from a large bitumen-tar deposit in Venezuela, and burned in power stations. It is mixed with water to allow transportation through pipelines and onboard oil tankers. Chemicals have to be added to hold the bitumen in suspension with the water.
Orimulsion is normally shipped in crude oil tankers, and shippers do not generally require any special cleaning after a crude oil cargo and prior to loading orimulsion.
While it might be difficult to imagine quality problems with such a low-grade cargo, there has recently been one case of receivers rejecting orimulsion as being off-spec. This was apparently because the orimulsion contained solid particles which were too large to pass through burners at the receiver's power station, or because the bitumen / water mix was not properly emulsified.
Although these problems appear to have occurred in the production stage, prior to loading, it is still recommended that ships in the trade take and preserve proper cargo samples in order to protect Members against any allegations of contamination or deterioration of orimulsion cargoes onboard ship.