Heater Tubes

[Anonymous]

With the vast amount of experience on the boards here, Id like to have some input on some heater issues we are currently having. On one of our heaters the bottom  3 tubes nearest the burners have become detached , and are no longer resting comfortably in their tube hangers, some have raised vertically about 6 to 8 inches out of the hangers themselves, while other parts have come completly out of the hangers all together, and appear to be suspended in mid-air, and bent, kind of like those bendable straws, as odd as it may seem. If you can visualize this description ( pictures to post later) or if you have seen or heard of something similar your input would be greatly appreciated.

[Anonymous]

It sounds like you have some sagging on those tubes.  There are certain allowances on how much tubes can bend or sagg from their respective hangers, but if the bottom tubes are touching the floor or are too close to the burner you are probably looking at shutting down and fixing the problem.  You may experience some burner impingement if the tubes keep getting too close to the burner.  Try to do some heat scans or some thermal images and see if that part of the heater has more heat than others.  Good luck.

[coked]

We had the same problem with sagging tubes. We check on the burners and replace those that have pinching flames. We also included a routine thermal inspection on the tubes to make sure there is no hot spot. 

[Ray Pollard]

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

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