ASTM-D2803:09(R2020) pdf free download – Standard Guide for Testing Filiform Corrosion Resistance of Organic Coatings on Metal.
8. Use of Control or Reference Materials
8.1 When several coatings are being compared, select a coating as a control. Apply the control coating to the same substrate as the test coatings. For best results there should be two controls, one known to perform well and one known to perform poorly.
9. Procedure A
9.1 Expose the test specimens to the salt-fog atmosphere in accordance with Practice B 117 for at least 4 h and not more than 24 h, or as agreed upon between the producer and user.
9.2 Remove from the salt-fog cabinet and thoroughly rinse with distilled or demineralized water. Do not permit specimens to dry before placing in the humidity cabinet.
9.3 Place the specimens in the humidity cabinet so that they are no closer together than 40 mm (1.5 in.) and not in contact with any metal. Set the cabinet to operate at 25°C (77°F) and 85 % relative humidity unless otherwise agreed upon between the producer and user. The allowed operational limits are ±2°C (±3.5°F) and ±10% relative humidity.
Nom 6—The recommended means of maintaining the specified relative humidity is to utilize trays of saturated potassium chromate solution (650 gIL). Practice E104 describes other methods for maintaining relative humidity. hut they may affect the degree and rate of fihiform corrosion.
9.4 Inspect the specimens at intervals of approximately 168 h for development of threadlike filaments from the scribe. Exercise care to maintain wetness of specimens during inspection, since drying stops the original pattern of fihiform corrosion. New lihiform may develop on continued exposure but at different points.
9.4.1 Filiform corrosion will be noted as threadlike filaments (see Note 7), initiating at the scribe. A standard method of rating failure due to fihiform is not available. The uniformity of filament growth in direction, width, height and frequency precludes a precise rating system. Photographs of tiliform failure are preferred for recording test results. Otherwise, a brief description of the filament growth and their frequency can he made. ISO 4628—10 provides a method for the measurement of tiliform filaments. Filiform corrosion may continue to develop after specimens are removed from the humidity cabinet.
Nom 7—The nawre of grinding and grain direction on panels can influence the direction of Illiform growth.
9.5 The normal test period is 6 weeks (1008 h). Other periods may he used at the option of the producer and user.
10. Procedure B (ISO 4623)
10.1 Two alternative initiations of corrosion are available, based on initiation by dipping in sodium chloride solution (see Note 8) or exposure to salt fog. The dipping technique is generally preferable for air drying and low-durability materials. For high-durability systems such as automotive finishes applied to phosphated steel, the dipping technique may not produce tiliform corrosion and for these systems, it is preferable to adopt the salt-fog technique.