3.1 The methanol wall wash test is performed to determine the cleanliness and suitability of cargo tanks or compartments on a marine vessel prior to loading polyester grade monoethylene glycol. Polyester grade monoethylene glycol has very high quality requirements and must be handled with care, as it is adversely affected by oxygen, hydrocarbons, water and chloride. It is especially susceptible to aromatic contamination, which degrades UV transmittance. Possible sources of contamination are the prior cargoes and cleaning agents. The methanol wall wash procedure provides a representative sampling of the impurities and contamination present on the sides of the cargo tank.

3.2 The test methods used for analysis of the methanol wall wash samples are capable of determining low levels of impurities or contamination in methanol. These tests include appearance, color, hydrocarbons and chloride. The producers of polyester grade monoethylene glycol need confirmation of the cleanliness and suitability of the marine vessel's tanks prior to loading with in-specification material. Cargo tanks that do not pass the wall wash test should not be loaded.

3.3 Alternative test methods and technology for several of the methods can be found in the Appendix. The alternative test methods do not have precision data for the application of these methods in analyzing methanol. Use of these methods is optional and individuals using the alternative methods should assure themselves that the method is sufficiently precise. Precision data is only for the original test methods listed.