Analysis of O-Ring Seal Failure under Static Conditions and Determination of End-of-Lifetime Criterion.

Anja Kömmling,Mikael Hedenqvist,Dietmar Wolff,Matthias Jaunich,Payam Pourmand

doi:10.3390/polym11081251

Abstract

Determining a suitable and reliable end-of-lifetime criterion for O-ring seals is an important issue for long-term seal applications. Therefore, seal failure of ethylene propylene diene rubber (EPDM) and hydrogenated nitrile butadiene rubber (HNBR) O-rings aged in the compressed state at 125 °C and at 150 °C for up to 1.5 years was analyzed and investigated under static conditions, using both non-lubricated and lubricated seals. Changes of the material properties were analyzed with dynamic-mechanical analysis and permeability experiments. Indenter modulus measurements were used to investigate DLO effects. It became clear that O-rings can remain leak-tight under static conditions even when material properties have already degraded considerably, especially when adhesion effects are encountered. As a feasible and reliable end-of-lifetime criterion for O-ring seals under static conditions should include a safety margin for slight dimensional changes, a modified leakage test involving a small and rapid partial decompression of the seal was introduced that enabled determining a more realistic but still conservative end-of-lifetime criterion for an EPDM seal.

Highlights

Due to their excellent elasticity and resilience, seals made of elastomers are widely used in many technical applications to prevent leakage of fluids
The temperature region where a drop in the storage modulus and a peak in the loss modulus is observed increased with increasing aging time. This indicated an increased glass transition temperature and hardening due to the dominant crosslinking reactions occurring during aging of hydrogenated nitrile butadiene rubber (HNBR) [17,18]
At −30 ◦ C, which is the lower temperature for leakage rate measurements in Section 3.3, the material is in the glassy state

Summary

Introduction

Due to their excellent elasticity and resilience, seals made of elastomers are widely used in many technical applications to prevent leakage of fluids. Like all polymers, elastomers age under the influence of e.g., oxygen, heat, time, UV radiation, and dynamic loads. For elastomer seals, both physical and chemical aging can deteriorate the seal performance. Physical aging involves reversible effects, e.g., relaxation through chain rearrangements [1,2], that lead to a loss of sealing force over time. Chemical aging involves irreversible processes such as oxidation, chain scission, and additional crosslinking. During aging of EPDM, generally both chain scissions (mainly in the propylene segments [16]) and crosslinking reactions (mostly via the termonomer [8]) take place [17]

Methods

Results

Conclusion