The experiences we have had appear to be the result of two different things. If the tubes are only sagging in between hangers we have attributed that to simple overheating. This used to happen a lot more often during “Steam Air Decoking” with less than Ideal control of the process.[ Poor operations] we no longer do “Steam Air decoking” Tubes coming out of the hangers were the result of “Uneven Heating of the length of the tube”. [we think.] This has happened mostly on lower tubes with a burner impinging on a tube causing that area to overheat, or some other upset causing the particular tube to “Move” in the hanger and eventually come out of the hanger, [they rarely return to the original position] We have not had a tube rupture but have shut down a coulpe of times to replace/repair the problem. Our engineers tell us there is an industry standard of maximum excursion without rupture, and that has driven our unscheduled shutdowns
