No Sir. Crack has stopped at the pit like dent like if you draw a straight line between 2 points. No crack beyond the pit like dent. > >Check if the cracks originated from the dented locations at >either ends of the crack tip. Fractograph taken would have >given some clues on this. > >Hope this helps >C.V.Srinivasan Nishi Engineers Pvt Ltd India April 13, 2008 >E-mail: nishi@vsnl.com >>Thank U Sir. >> >>I missed to point out that at both the extremities of the >>crack tip there exist visible shallow dent. >> >>regards>Debasis >>> >>>Your furnace tube - P 9 - had seen external wide mouth >>>cracks seen upto 70% - outer to inner wall thickness (from >>>what is described). >>> >>>This could be probably due to impingement from flames or >>>direct impingement from burner nozzle - fuel configuration >>>not kept properly. >>> >>>Localized over-heating and short term stress-rupture due to >>>over heating from flame impingement is a common phenomenon >>>seen in such burner (burner nozzle angles not kept) >>>impinged tubes ( whether related to steam-boiler water wall >>>tube failures or in furnace tubes in refinery heaters). >>> >>>LME is a different phenomenon which external Al painting - >>>if it had penetrated would have shown as intergranular >>>cracks. For this heater coil should have seen around 650 deg >>>cent at least. >>> >>>At 650 deg cent, P 9 would have shown other effects - viz., >>>more creep related voids and cracks. The fact that you had >>>seen only isolated creep voids - to me it appears - this may >>>not be a cause. >>> >>>Point raised by Krish - on hammer test ( No one does sledge >>>hammering but in some refineries still slight tapping only >>>is done during hydro test period). Slight hammer tapping >>>will not be a big stress raising area to cause stress >>>rupture. No one does a sledge hammer test during hydro test. >>> >>>Still evidence of this would have been noted from >>>metallography. Your description did not indicate the same. >>> >>>Fish mouth rupture in heater coil is mostly due to direct >>>flame impingement. Please examine from this angle. >>> >>>Hope this helps >>>C.V.Srinivasan Nishi Engineers Pvt Ltd India April 11, 2008 >>>E-mail: nishi@vsnl.com >>> >>>>A typical longitudinal, linear, wide mouth, unbranched >>>>external crack noticed in one 9cr-1Mo H-Oil Furnace Tube . >>>>The crack has propagated approx. 70% WT from outside and not >>>>through. >>>> >>>>By careful partitioning of the crack face fractography done >>>>and surprisingly by EDX some high level of "Al" peaks are >>>>seen alongwith isolated population of creep voids. >>>> >>>>We are quite confused with the presence of "Al" peaks which >>>>could have been happened if there was any Aluminium paining >>>>etc. >>>> >>>>If anyone can share regarding possibility and any reference >>>>of Liquid Metal Embrittlement of P9 tube by "Al" it will be >>>>of help. Or any other discussion >>>> >>>>regards

Luis Crack - seen in P 9 material - had reportedly occurred from external to internal wall upto 70% ( please read first communication by Debasis on description of failure). Creep, as you are aware, is an internal to external fissure phenomenon most likely to start at mid wall and propagate to both inward and out ward of the wall thickness. Description given by Debasis did not indicate this. This may not be the cause of failure of this P 9 material tube. To me it looks like flame impingement from burner configuration change on external wall of the particular tube to get this failure. Coking problem, raised by you in your query, would have promoted internal to external wide mouth cracking with external hot spot supply. Cracks seen were from external to internal upto 70%. Considering this coking may not be the cause for the failure. Hope this helps you C.V.Srinivasan Nishi Engineers Pvt Ltd India April 24, 2008 E-mail: nishi@vsnl.com >How old are the tubes? > >Have the tubes been initialy submitted to calorizing or >aluminizing? > >It seems that your failure was due to creep under some hot >spot operation condition. > >Is it possible to know the tube skin temperatures?coking >condition?At the time of the rupture. > > >Regards > >luis marques