The 36 in. diameter retort was previously constructed from RA330 alloy. Operating temperatures average 1950 F. RA330 retorts typically lasted eight months before distortion required repair of the sidewall near the flange. Sharp thermal gradients in this area lead to distortion. RA 353 MA was selected due to its very high creep strength. At 1900 F, RA 353 MA offers more than double the stress rupture strength of RA330. After 24 months of service, the RA 353 MA retort has not required repairs. As a result, RA 353 MA is now specified for all retorts.