Visual inspection of paint film

Inspect the surface condition of the paint film with the naked eye, and the paint film should be free of defects such as pinholes, bubbles, cracks, peeling, sagging, and missed coating.

(1) All projects covered by this specification must be inspected by the purchaser, and any projects found to have not complied with the specification shall be reworked until satisfactory to the purchaser. (2) The purchaser can randomly sample and inspect the painted materials, equipment, etc. by using acetone to paint small samples onto exposed metal and inspecting the surface with a magnifying glass to observe whether there is rust under the primer layer. The supplier shall repair and repaint the non-conforming parts at their own expense. (3) The dry film and wet film thickness can be determined by using a meter. (4) When checking the amount of diluent added, a viscosity cup can be used to determine the viscosity of the paint in the bucket and compare it with the value obtained from the manufacturer. The inspection of the amount of diluent added, the viscosity of the paint in the tank can be determined by comparing it with the value provided by the paint manufacturer by pouring the paint into a cup. (5) The continuity of the paint film on the metal surface can be checked by a low-pressure holiday detector. Insufficient coating areas should be marked with chalk. If five or more defects are found within an area of 10m2, it can be considered that the entire area has defects. (6) The surface temperature can be measured using a surface thermometer. The moisture content on non-metallic surfaces can be measured using a moisture analyzer. (7) The paint should have sufficient adhesion to prevent a layer of hardened paint from peeling off when the putty knife blade is inserted underneath. The interlayer adhesion force should be such that when using a sharp knife test, two or more hardened coatings should not delaminate. Paint should have sufficient adhesion, and when a putty knife is inserted into the bottom of the paint film, it should be able to prevent the hard paint film from becoming a layer and being lifted up. The adhesion between each layer should also be sufficient, and there should be no delamination when using a fast knife to measure the adhesion between two or more layers. (8) Each coat of paint, such as primer and intermediate coat, should be free from dry spray, splashing, small pores, and discontinuities as much as possible. The appearance can be checked according to the table below, and areas that do not meet the requirements should be repainted.

Paint film thickness inspection

During construction, the coating should be carried out according to the usage amount, and the dry film thickness (DFT) should be measured frequently with a paint film thickness gauge. After each coating, the thickness of the paint film should be measured, and the total thickness of the paint film should be measured after the coating is completed. For edges, corners, welds, cuts, and other areas, a coat should be applied before spraying, and then a large area of coating should be carried out to ensure the thickness of the paint film on the protruding parts. In general, the distribution of paint film thickness should be controlled within two 90% or more, which requires that the dry film thickness values measured at more than 90% of the measuring points must reach or exceed the specified dry film thickness value, and the dry film thickness values measured at the remaining less than 10% of the measuring points must not be lower than 90% of the specified dry film thickness value. Otherwise, a touch up or additional coating should be applied. The selection of measuring points should be representative, and the frequency of testing should be determined based on the specific conditions of the coated surface. In principle, one point should be measured every 1-3 square meters (or as otherwise specified, for flat surfaces, one point can be measured every 10 square meters, and for complex surfaces, one point can be measured every 5 square meters. For small areas or components such as narrow cabins and small liquid tanks, there are three or more measuring points per free surface.)

Measurement of paint film thickness

Every time a layer of paint is applied, the film thickness should be measured, and the total thickness should be measured before leaving the factory. After on-site touch up painting and topcoat application, the final film thickness measurement shall be carried out. Measurements can only be taken after the paint film has completely dried. If the minimum dry film thickness required cannot be achieved according to the dry film verification, additional paint coating should be applied to obtain the specified thickness. Set a measuring point every 10m2 during component measurement. The thickness of dry and wet paint film can be measured using a film thickness gauge or Nordson micro meter. The discontinuity of the metal surface paint film can be checked by a low-pressure detector. The surface temperature of metal can be determined by using a surface thermometer.

Judgment criteria

If 5 or more defects are found on a 10 square area, the purchaser may consider the entire area to have paint defects. 90% of the measurement points require the paint film thickness to meet the specified standard value. For points that do not meet the specified standard value, the thickness of the paint film shall not be less than 90% of the specified standard value, otherwise, repainting shall be applied.

Adhesion test of paint film

The adhesion test of paint film should follow the 0-1 level standard

Topcoat adhesion test -->Topcoat film thickness test -->Primer adhesion test -->Sample film thickness test