Seal life of EPDM O-rings at high temperature determined by unique method

Abstract

A recurrent concern in the design of packaging for the transport of radioactive material is to determine the life of the elastomeric O-ring at high temperature. Most O-ring suppliers specify maximum allowable temperatures during 'continuous service' and 'peak service' (such as '200°C in continuous service' or '250°C in peak') but they do not specify the definition of 'continuous' or 'peak' service, the acceptance criteria or how these maximum temperatures are determined. It is difficult on the basis of these types of data to assess the acceptability of an O-ring submitted to fluctuating temperatures. Cogema Logistics has launched a test programme to determine the maximum seal life at different temperatures (e.g. 200°C, 210°C,…, 250°C…) of the different rubber grades used on its casks, based on clearly defined criteria. The goal is to establish, for each rubber grade, the seal life versus temperature curve. These curves can be used to determine if an O-ring exposed to any specified temperature profile can guarantee leaktightness. The principle of the method is to calculate a sum of 'elementary damage rates' on the temperature profile (split up into elementary time intervals) and to compare this sum (the 'global damage rate') with a 'maximum permissible damage rate'. If the global damage rate is lower than the maximum permissible damage rate, the leaktightness of the packaging can be guaranteed for the given temperature profile.

Keywords:

• EPDM
• O-RINGS
• HIGH TEMPERATURE
• SEAL LIFE