Full definition
Seal chemical compatibility is a critical factor in the selection of seal and gasket materials, determining how well these materials will perform when exposed to different fluids and environments. The ability of a seal to maintain its integrity and functionality when in contact with the intended fluid is essential to prevent leaks and ensure system reliability. Incompatibility can manifest in several ways: excessive volume swell can lead to oversized seals that become extrudable, while hardening or embrittlement can occur due to cross-link scission, resulting in cracks under compression. Additionally, softening may happen due to plasticizer extraction or polymer chain scission, causing a loss of sealing force. Surface cracking may indicate a chemical attack on the seal's surface, and in extreme cases, complete dissolution of the material can happen. Each of these failure modes can have severe implications for system performance and safety.
To evaluate seal chemical compatibility, a common method involves immersing the specimen in the specific fluid at the expected service temperature for a duration of 70 to 168 hours, as per ASTM D471. After this exposure, critical parameters such as volume change, hardness change, and tensile or elongation change must be measured. Understanding the nuances of various elastomeric materials is key; for instance, Nitrile Butadiene Rubber (NBR) is compatible with oils, fuels, and greases but is not suitable for ketones or esters. Ethylene Propylene Diene Monomer (EPDM) is often used for water, steam, and acids, but not for mineral oils. Fluoroelastomer (FKM) provides good compatibility with a wide range of chemicals except for amines and hot water. Silicone elastomers can withstand wide temperature variations but may not perform well in steam or hydrocarbon solvents. Perfluoroelastomer (FFKM) offers exceptional chemical resistance across a broad spectrum but comes at a higher cost, typically ranging from $50 to $500 per seal.
It's crucial to verify compatibility with the specific fluid at the actual service temperature, as generic compatibility charts serve only as preliminary guidance. Manufacturers such as Parker, Trelleborg, and Freudenberg provide detailed chemical resistance guides that can aid in the selection process, ensuring that the chosen seal material will perform effectively under the anticipated operating conditions.