Method of determining diametrical growth of reformer tubes

A method for determining diametrical growth in a reformer tube comprising:

• providing a reformer tube having a circumferential reference marking on the outside of the reformer tube achieved through welding at least one metallic ring on the outer surface of the reformer tube;
• measuring a first set of outside diameters at a time t1 along a predefined length of the reformer tube that contains the circumferential reference marking(s) as well as at least a portion of the tube that while in operation gets heated to a temperature greater than 1300° F.;
• measuring a second set of outside diameters along the predefined length of the reformer tube after operating the reformer tube for an additional period of time, Δt, where t2=t1+Δt;
• aligning the second set of diameter measurements using the circumferential reference marking and a second available reference point to ensure that the axial locations of the entire length for the measurements from time t1 are the same as the axial locations of the entire length of the measurements from time t2;
• and
• calculating creep strain along the length of the tube by dividing the difference in diameter measurements at times t1 and t2, by the diameter measurement at time t1, for each location along the length of the tube, thereby determining diametrical growth in a reformer tube.