Bulk items such as cast and forged valves are commonly to be installed randomly without information on operating conditions. Therefore, inorganic copolymer coating products covering a wide temperature range are applied with a thickness of 250 μm (10 mils) to 300 μm (12 mils).
The inorganic zinc coating system is also able to be applied in a wide temperature range, but it is limited to up to 400°C (752°F) due to the zinc melting point of 420°C (788°F). However, if zinc coating is not applied as a topcoat, it may be retarded from being oxidized even at high temperatures. Thus, considering the application of a mixed coating system of inorganic zinc and inorganic copolymer, the complex cycling test of the heating furnace at 540°C (1004°F), QUV exposure, and salt spray was carried out for 3 months to compare with the inorganic copolymer system for coating performance. As a test result, it is confirmed that applying a mixed coating system composed of inorganic zinc and inorganic copolymer to a bulk valve is a suitable and optimal system under various temperature conditions for improving anti-corrosion performance and adhesion performance.
Bulk items such as cast and forged valves are installed under various temperature conditions as shown in Table 1. It is exposed to a wide range of temperatures, therefore the coating product applied to bulk items should have appropriate heat resistance performance. However, it is very difficult to select a suitable coating system since the temperature condition is not determined in the valve manufacturing stage. For this reason, unsuitable coating systems are often applied, causing coating defects in the field operation. Therefore, it is necessary to apply a coating system that can cover a wide temperature range to prevent this problem.
Paint manufacturers have developed heat resistance paints that can cover the wide temperature range of minus 196°C (-321°F) to 650°C (1202°F). It is an inorganic copolymer or an inert multi-polymeric matrix coating covering various temperature ranges for bulk items and the coating products are required to be applied to a thickness of 250μm (10mils) to 300μm (12mils) to ensure sufficient anti-corrosion performance.
