Proper compression of a gasket in a hygienic clamp (Tri-Clamp®) union is critical for consistent sealing of the connection and reproducible clean in place (CIP) processes. An under-compressed gasket is prone to leaks and possible entrapment areas between the gasket and ferrule. Excessive compression typically results in high stresses on the gasket material, clamps and ferrules often leading to premature failure. Furthermore, over-compressed elastomeric gaskets can lead to excessive intrusion of elastomer into the pipe lumen. Subsequent thermal cycling can magnify this effect; see the figure on the right. Since intrusion serves as a dam at the connection, it prevents complete draining and makes cleaning more problematic. While achieving the correct compression is important during installation, measuring compression is difficult in the field, to say the least. Controlling the torque applied to the clamp is an approach used by many biopharmaceutical manufacturers as a substitute. While prone to other variables such as friction loss, controlling the applied torque does provide a standardized installation process and therefore more consistent gasket compression.
There are no specific industry requirements for the proper torque setting of a hygienic clamp (Tri-clamp®) fitting, nor can there be. The correct torque setting is directly related to the properties of the seal material. Generally speaking, softer materials like elastomers (EPDM, Silicone) require less torque than more rigid materials (PTFE, PTFE/SS blends). Common practice in the industry uses torque ranges from 25-30 inch pounds for elastomers and 50+ inch pounds for the PTFE and PTFE blend materials.Typical Applied Torque Settings
Since the required compression, and therefore torque, can vary even between different formulations of elastomers, the seal manufacturer is best positioned to indicate the proper torque requirements for their gaskets. In fact, the 2009 edition of the ASME-BPE Standard requires that seals used in bioprocessing meet either Category I (+/- 0.025") or Category II (+/- 0.008") intrusion classification after initial installation. In specifying the intrusion category, the seal manufacturer must also provide an installation method that includes torque. For example, James Walker Elast-O-Pure EP75 Black™ gaskets meet Category I and in some cases Category II requirements when tightened to 30 in-lbs.