Components with large surface areas are often cleaned with a high-pressure washer. Paints and other coatings need to be able to withstand these pressurized water jets.
The degree of resistance of a coating on a component to such a cleaning process can be simulated with a pressure water-jetting test. In this the damage that a pressurized water jet can cause is not only dependent on how well the coating adheres. The water pressure, water temperature and duration of jetting influence the degree of damage, as does the distance of the high-pressure nozzle to the component tested, the geometry of the nozzle and the surface area impacted.
ISO standard 16925 of the International Organization for Standardization (ISO) exists to ensure the worldwide comparability of the results of such tests. The German version is DIN EN ISO 16925 coatings – testing of resistance of coatings to water jetting.
A number of examples for the uniform procedure of the standard:
Experts compare the test results with images from the ISO 16925 standard and assign the separated surface areas or cracks co-efficients of from 0 to 5 for the test report. A co-efficient of 0 corresponds to very good adhesion with water jet impact, a co-efficient of 5 a very poor one.
Co-efficients from 1 to 5 are supplemented with a letter specifying the type of damage: the letter “a” is added where the coating breaks off along the longer cut. The letter “b” is selected where the damage is local, at one or more points. Experts use the letter “c” to indicate that the coating has not flaked off, but that cracks are formed.
If the resistance of a multi-layered coating is tested in this way, it is also investigated whether only the top coat flakes off, or also the base coat.