How to check the water vapor permeability of rubber and plastic insulation pipes

How to check the water vapor permeability of rubber and plastic insulation pipe The water vapor resistance of insulation material is an important factor affecting its service life. Therefore, it is necessary to test the water vapor permeability of rubber and plastic insulation pipes, which is one of the indicators that related enterprises must pay attention to and control. This paper briefly introduces the water vapor permeability test of rubber and plastic insulation pipe in combination with water vapor transmission rate tester.

1. Significance of water vapor permeability testing for rubber and plastic insulation pipes

For the realization of the insulation ability of rubber-plastic foam insulation materials, it relies on a large amount of gas inside the tiny bubbles. In a reasonable range of bubble diameters, the more complete the foaming, the higher the gas content in the material, and the better the heat insulating effect. In actual use, there is always a temperature difference and a humidity difference on both sides of the inner and outer walls of the rubber-plastic insulation pipe, which forms a difference in partial pressure of water and gas, and the water gas gradually penetrates into the interior of the material. Because the thermal conductivity of water (0.599w/m·k, 20°C) is much higher than that of air (0.026w/m·k, 20°C), the thermal conductivity increases with the accumulation of internal moisture. Lead to reduced or lost thermal insulation and reduced service life. Therefore, the water vapor permeability resistance of the insulation material is very important, which is directly related to the service life of the material. The stronger the resistance to water vapor permeation, the more difficult it is for water vapor molecules to penetrate into the interior of the material. The slower the thermal conductivity increases, the longer the service life of the thermal insulation material. For rubber-plastic insulation pipes, the ability to resist water vapor permeation can be characterized by the water vapor transmission rate of the material.

2. Method for testing water vapor transmission rate of rubber and plastic insulation pipe

The water vapor transmission rate test of rubber and plastic insulation pipes mainly refers to the standard: BS EN 13469-2001 "Insulation products for building equipment and industrial facilities, and determination of water vapor transmission rate of prefabricated pipe insulation layers". This standard requires the test chamber environment to be controlled at a constant temperature and humidity of (23 ± 1) °C and relative humidity (50 ± 3)%. The air velocity in the chamber is between 0.02 m/s and 0.3 m/s. The intercept height of the sample is (100 ± 1) mm. If the outer diameter of the sample is larger than 100 mm, it is taken at 150 mm. Keep the section as smooth as possible. A certain amount of desiccant (providing a 0% humidity environment) was placed inside the sample, and the upper and lower ports were sealed with aluminum foil. Thus, there is a humidity difference between the 0% humidity inside the sample and the 50% humidity in the test chamber, and the water vapor in the test chamber will penetrate into the inside of the sample. The water vapor transmission rate can be calculated by periodically weighing the sample cup.