Porosity testing of enamel coatings on equipment used in the chemical and pharmaceutical industries
Because it is impervious to high temperatures and chemically reactive substances, vitreous enamel makes an excellent anti-corrosion barrier for the boilers and tanks used in the chemical and pharmaceutical industries. But this protection is only guaranteed if the coating is 100% continuous and has no pores, cracks, or other defects that could allow exchange between the equipment and its contents. This requires a reliable porosity test.
Steel tanks, pipes and mixers are often used in the manufacture of chemical and pharmaceutical products. To protect these parts from corrosion, they are coated with enamel 0.8-2.4 mm thick, depending on the requirements at hand. To ensure 100% protection, the enamel must be checked for gaps: To this end, the ISO 2746 standard test for enamelled articles for service under highly corrosive conditions specifies that the electrode of a high-voltage probe be moved slowly across the surface of the enamel. If the layer’s electrically insulating effect is interrupted (indicating a pore), the voltage drops suddenly. It is this voltage drop that is detected and signalled by the testing instrument.
Fig.1: Porosity test using the POROSCOPE® HV20 on a container in a chemical plant
The new POROSCOPE® HV20 is perfectly suited for the porosity testing of enamel coatings. The robust design of the probe head ensures longevity and meets all safety requirements for working with high voltage. Depending on the topology of the object to be tested, various electrodes are available for use, including flat brushes, sweepers or smaller whisks for testing inside of cavities.
Fig.2: Different electrodes are available for porosity testing
Porosity testing ideally takes place right after the enamelling process. The voltage applied is typically between 12 and 20 kV, depending on the thickness of the enamel layer. Based on the values laid out in the ISO 2746 standard, the correct voltage can be set directly on the probe head. Regular porosity evaluation during the fabrication of such pipes, tanks and mixers is the only way to verify the integrity of the enamel – a critical barrier that not only provides for corrosion protection of these components but also safeguards against contamination of their valuable contents.
The new POROSCOPE® HV20 is ideal for high voltage porosity testing of the vitreous and porcelain enamel coatings often used on equipment and infrastructure for the chemical and pharmaceutical industries. The adjustable range of 4-20 kV ensures that all common thicknesses can be reliably checked for defects such as cracks, pores and other weaknesses. For more information or a demonstration of the POROSCOPE® please contact your local FISCHER representative.