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Pressure water jetting test

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PRESSURE WATER-JETTING TEST

Components with large surface areas are often cleaned with a high-​pressure washer. Paints and other coatings need to be able to withstand the forces associated with 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 test, the damage that a pressurized water jet can cause is not solely dependent on the adhesion properties of the coating. Other factors include:
 

  • The water pressure
  • The water temperature
  • Duration of jetting
  • Distance of the high-​pressure nozzle to the component tested
  • The geometry of the nozzle and the surface area impacted.
     

The pressure water jetting test is specified by the standard ISO 16925
 

The test procedure follows below:
 

  • Two straight cuts are etched into the coating of the component. The minimum length of the first cut is 100 mm and the length of the second cut is at least 20 mm long. Both cuts are made at an angle of approximately 30° to each other.
  • The component is secured in the test chamber of the pressure water-​jetting device. The distance between the high-​pressure nozzle and the sample is 100 or 130 mm. If the shorter distance is chosen, the pressure is higher. The geometry of the nozzle is also defined.
  • The water jet impacts the component vertically at a right angle (90°). It is aimed directly at the interface of the two cuts.
  • The sample is subjected to a jet of de-mineralized water heated to 60°C for 30 or 60 seconds. If the longer time is selected, the coated part is subjected to greater stress.
     

The flow quantity is 11.3 l/min.
 

Water pressure at nozzle outlet is 68 bar.
 

Immediately after the test, the degree of separation or cracking is assessed with the naked eye.
 

Experts compare the test results with images from the ISO 16925 standard and assign the separated surface areas or cracks rating on a scale of 0 to 5 for the test report. A rating of 0 corresponds to very good adhesion with water jet impact whereas a rating of 5 is a very poor result.
 

Ratings 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 located 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 a multi-​layered coating is tested, it is also determined if the loss of adhesion occurs only in the topcoat layer or within the basecoat as well.

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