Abstract
A metallurgical evaluation was conducted involving a 316Cb tube removed from an atmospheric distillation unit heater, after 18 years of service. Since this steel is not a standard material for heater tubes, the design used creep properties from type 347 stainless steel tube. A tube sample was submitted for remaining life assessment. The material properties reported for type 347H stainless steel were used for this study. The creep tests were conducted following the Omega method, but LMP data were also derived to make an assessment based on this method as well. Applying both methods, the type 316Cb steel appeared creep stronger than 347H steel. The 316Cb steel in this tube sample did not undergo significant microstructure degradation and creep life consumption, thus, estimation indicated ample remaining life for future service. Type 316H steel was not used as reference because the original design used type 347 stainless steel tube properties to determine the required wall thickness.
