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In our FCC, we are facing problem i.e. flue gas line TSS-FSS flange leak, causing heavy erosion of the flange and catalyst loss through the leak. Therefore, i request you to confirm whether is it possible to do lip seal joint for these flanges or any other parameter to check the compatibility for lip seal joint of these flanges..
 
Answers
10/04/2016 A: Peter Marsh, XBP Refining Consultants Ltd, peter.marsh@xbprefining.co.uk
I agree with Eric Hennings. Erosion leaks typically only get worse and the rate of erosion tends to increase with time. If the TSS-FSS line cannot be isolated temporarily to enable a permanent repair to be made then the safest option is to shutdown the FCC to carry out the repair. An external clamp fitted around the leak and filled with sealant will be difficult to install and probably won't last long in this service.
I recommend you carry out a failure analysis to determine the root cause of the leak. If the TSS-FSS line is fabricated from 304H stainless steel or similar, polythionic acid stress corrosion cracking (PASCC) may have caused the initial loss of containment and erosion by escaping catalyst particles will have exacerbated the problem. In this case, a lip seal joint in the same metallurgy would provide no additional protection. A better solution would be to ensure procedures are in place to avoid operating conditions which promote sensitisation of the steel and avoid condensation of moisture and acidic components. Furthermore the TSS-FSS piping layout should be arranged to avoid deadlegs which would allow accumulation of acidic components.
04/04/2016 A: Ed Versluis, James Walker, ed.versluis@jameswalker.biz
Have done in 2013 a in depth study on hot wall flue gas flange designs on a FCC unit. The problem on these flange connections was that the pipe line from third stage separator to the expander was not refractory lined and therefore flange materials functioned in the creep region of 700°C (1300°F). Therefore the bolted joint connections are extremely sensitive for overloading and subsequent flange leaks. Previously 25% of all the hot wall flanges connections leaked back in 2012 and were ASME B16.47 series B flange designs in a SS304H stainless steel configuration, some flanges in B16.5 in class 600#. We resolved the issue not by the use of a lip seal but just a spiral wound gasket with high temperature filler. But more important we reduced the bolt area on the flange by at least 40% by the use of bolt collars to prevent the flanges from overloading in the elevated conditions. As the pressure is just only maximum 2 bar, while flange connection is designed for 55 bar pressure. The big bolt area is causing additional issues in the elevated conditions. This turned out extremely positive and we've a successful solution now for hot wall flange connections as these are all free of leakage since the implementation back in 2013. If you need more details please revert back to me.
22/02/2016 A: Eric Hennings, Technip Stone & Webster, EHennings@technip.com
Once a erosion leak starts, it usually gets worse. Refiners have “boxed in” leaking flange using a retaining ring, but it must be filled with a pumpable sealant-as there will be leaks in gaps at stud bolts. Consider stresses in the design.