Estimation the Remaining Life for Reformer Unit Tubes Furnace Operated Beyond the Design Life

Abstract

The aim of this work is to study and model creep damage accumulation for remaining safe working life estimation of tube material used in petroleum industry plants operated at a high temperature for long time beyond the design life. Material constants and other data required for life estimation were extracted from the output results of real accelerated creep rupture tests conducted at three test temperatures (700, 725, and 750(oC and at three constant stress applications (120, 130, and 140 MPa). Also, a time-temperature parameter method (Larson-Miller Method) was modified to be applied based on the results of the accelerated creep rupture tests to build life predicted master curve for austenitic stainless steel type 321H. It is found that creep rupture time for stainless steel alloy decreases as temperature or stress increase. Also, it distinguished from the creep curves for the serviced stainless steel alloy, that the onset of tertiary creep stage starts early (about 50% of creep curve), this reflects the reduction in creep strength of the alloy as a result of the degradation in alloy properties that take place during the service life. It is also found that the estimated remaining working life for the serviced tube samples made from austenitic stainless steel type 321H is about (54703 hr) based on the calculated stress level (40 MPa) and service temperature 570 oC. The difference between the estimated remaining life and the experimental creep test life is due to the differences between the applied stresses, where higher level of stresses in the experimental creep testes are used to accelerate failure of specimens. The application for the result of this work can be the petroleum industries that where heaters tubes serviced at such industry need to be estimated for the remaining life after the design life expire.