MC-99-93 Metallurgical Condition and Remaining Life of FCCU Vessels After 30 Years Operation

Description:

The project has shown that heavy section carbon-manganese and 1¼CrMo steel components which have operated at temperatures of ~1000°F for very long periods (in excess of 30 years), and which exhibit soft and severely over-aged microstructures, are capable of retaining high levels of creep rupture strength and can be underwritten for further long periods of secure operation provided the rupture strength levels of the welds are determined by testing. It may, as in this case, be possible to substantiate a significant increase in secure operating temperature based on the test results. The effect implies the occurrence of an hitherto unsuspected creep strengthening mechanism at times in excess of 15-20 years which, depending on its generality, may have significant implications for the continued operation of old plant.