Wall wash testing for chemical tanker cargo tanks
The commercial tank acceptance test measured against the cargo's product specification, its permanganate time, colour and chloride limits, and why no IMO instrument requires it.
A wall wash test is the tank acceptance test carried out before loading a high-purity chemical parcel. Solvent, usually laboratory-grade methanol, is washed down measured areas of the tank bulkheads and collected, and the collected liquid is analysed against the purity specification the cargo is sold under.
No provision of the IBC Code or of MARPOL Annex II requires a wall wash. It is a commercial acceptance regime, not a statutory one: the cargo buyer writes the specification into the voyage instructions and the loading terminal’s independent surveyor takes the samples for shore laboratory analysis. Failing the test does not make the ship non-compliant. It makes the ship unable to load that parcel, which is commercially worse and is why a wall wash failure is a serious operational event.
For methanol, the commonest case, the governing document is the IMPCA Methanol Reference Specifications, version 10 of 25 October 2024, whose parameters include a permanganate time of at least 60 minutes at 15 degrees C by ASTM D1363, a platinum-cobalt colour of 5 maximum by ASTM D1209, chloride at 0.5 mg/kg maximum by IMPCA 002-98, and a hydrocarbon miscibility pass by ASTM D1722. The shipboard result is indicative and the loading decision rests on the shore analysis. The full article will cover the sampling practice, the supplementary tests, and how coating memory in an epoxy-lined tank complicates the interpretation.