Study on the lifetime of EPDM seals in nuclear-powered vessels

DCNS provides the French Navy with ships and services, including through-life support (TLS). For that activity, the lifetime of seals has to be studied, either because periods between maintenance stops are longer, or because some seals cannot be replaced in short time and without removing big equipments.Among different kinds of seals we studied, we focus on EPDM seals. First of all, we studied their thermal ageing in service, through accelerated ageing procedures and Arrhenius law. Their mechanical properties after 19 and 32 years were estimated. They showed a reasonable evolution.Then, the effects of gamma-radiations were studied at different doses: 10, 20 and 400 kGy combining temperature and radiation and 18, 33 and 250 kGy (only radiation). In both cases, seals were irradiated after thermal ageing.Mechanical properties (compression, tensile, and hardness) were measured at the surface and in the middle of the seals (10×10 mm2 section and 68 mm diameter). In addition, physicochemical tests were performed (TGA and DSC).The results showed that in normal conditions, the properties of the EPDM seals vary a little till 32 years in service (<20% in compression, and <30% in elongation at break in tension).On the other hand, with doses of 250 and 400 kGy, the evolution of the seals is important (+130% compression force).These results are in good concordance with other studies on this kind of polymer, where the dose at which there is a significant modification is about 250 kGy (Madani, 2004 and Zaharescu and Podina, 2001).