Chemical and Thermal Compatibility in Filtration – Part 1

This first article in a two-part series focuses on chemical and thermal compatibility in industrial cartridge filtration. However, the tenets in this document are not limited to industrial cartridge filtration and can be applied to other filtration and separation equipment.

Chemical and thermal compatibility of the components of a filter element and filtration system with the fluid process are essential to successful filtration. If any part of the filter or filtration equipment is compromised during start-up, the filtration operation or shutdown of the fluid process, due to incompatibility, not only will the filtration be unsuccessful, but it also could create a very hazardous and unsafe situation for operations. Therefore, it is critical that a full review of chemical and thermal compatibility with all components be conducted during the design phase of a filtration system.

Material incompatibility can come in many forms, including this short list:

• Dissolved filter materials from solubility of material in fluid
• Swelling due to absorption of process fluid into the filter components
• Shrinkage from components in material being extracted from the filter
• Leaching of filter component materials into fluid, causing downstream contamination
• Melting of filter components due to thermal incompatibility
• Softening of filter cap potting materials due to chemical attack
• Fracturing of materials due to brittleness or thermal shock
• Corrosion of metal components
• Hydrogen-induced or stress corrosion cracking of metals

Chemical compatibility and thermal compatibility are not independent of each other. In fact, they are very much dependent on each other and need to be considered collectively. For example, higher temperatures increase kinetic energy, which increases chemical activity, or the movement of molecules, in the fluid, which increases contact of the molecules of the fluid process with the components of the filter. Increased contact can increase chemical attack on a material, which can have a significant impact on compatibility. Additionally, the system design engineer must consider compatibility with all conditions to which the filter elements and all wetted parts of the pressure vessel will be subjected during their life (defined as the exposure time to the conditions). Exposure time is a critical part of the compatibility evaluation because chemical attack is a time dependent process. The size or thickness of the filter components and how much of the component is actually exposed to the fluid will also come into consideration. In short, compatibility goes beyond the filtration process operating conditions.