Significance and Use

5.1 The water-break test as described in this test method is rapid, nondestructive, and may be used for control and evaluation of processes for the removal of hydrophobic contaminants. A water-break “free” test is commonly used for in-process verification of the absence of surface contaminants on metal surfaces that may interfere with subsequent surface treatments such as priming, conversion coating, anodizing, plating, or adhesive bonding

5.2 This test method is not quantitative and is typically restricted to applications where a go/no go evaluation of cleanliness will suffice.

5.3 The test may also be used for the detection and control of hydrophobic contaminants in processing environments. For this application, a witness surface free of hydrophobic films is exposed to the environment and subsequently tested. The sensitivity of this test will vary with the level of airborne contaminant and the duration of exposure of the witness surface.

5.4 For quantitative measurement of surface wetting, test methods that measure contact angle of a sessile drop of water or other test liquid may be used in some applications. Measurement methods based on contact angle are shown in Test Methods C813, D5946, and D7490; and Practice D7334.

5.4.1 Devices for in situ measurement of contact angle are available. These devices are limited to a small measurement surface area and may not reflect the cleanliness condition of a larger surface. For larger surface areas, localized contact angle measurement, or other quantitative inspection, combined with water-break testing may be useful.

5.5 For surfaces that cannot be immersed or doused with water, or where such immersion or dousing is impractical, such as previously coated large parts or assemblies, prior to the application of paints, primers or other organic coatings, Test Method F21 may be better suited for the evaluation of surface cleanliness than this test method.

Note 2: This test method is not appropriate where line of sight evaluation is not feasible; or for assembled hardware where there is a risk for entrapment of water in faying surfaces or complex structures where it may not be effectively removed.