USP Class VI is a biological reactivity classification associated with tests under USP chapter 88. It tells you about the tested compound and test conditions. It is useful evidence when a pharmaceutical specification calls for it. It does not by itself say that a seal is suitable for your product, CIP chemicals, steam cycles or mechanical duty.
Ask the supplier for the certificate for the exact compound, not just the words “USP Class VI” beside a broad material family. Check that the supplied part can be traced to the compound declared. Then check chemical resistance, temperature, compression set and the actual product contact requirements separately. Where extractables or leachables matter, the site quality team should assess the material and its intended use. A Class VI result is not a substitute for that assessment.
I treat Class VI as one part of a specification, not a promise of seal life. A seal can meet the requested biological test and still leak after repeated steam cycles if the grade is wrong for the duty.
Andrew Sykes | Acumen Seals & Pumps Limited | Independent mechanical seals and sealing specialist