As advised by Mr.CVS grid blasting may not be required for taking Metallography samples.Along with Metallography you can also check for the hardness using Ultrasonic Hardness Testing(to check thru'thickness hardness)to assess the fire damage.If necessary yu can think of replacing the affected portion if the out of roundness/bulges is very alarming.Further check the verticality of vessel due to fire damage. Since the tower top portion will experience less temperature during normal operation as compared to bottom flash zone you can think of providing additional external patch to run the vessel for some time until replacement during next shutdown. regards,

Debasis Hardness values given and micro structures seen (described) do not seem to indicate any significant metallurgical transformation in the affected portions of the vessel to cause worry. As a metallurgist, you should be able to distinguish and interpret results of this micro structure. Hope this helps you C.V.Srinivasan Nishi Engineers Pvt Ltd India March 27, 2008 E-mail: nishi@vsnl.com >If the structure demonstrates a ferrite/peralite structure >where perlite phase seem as onset of dissotiation but not >fully dissotiated to spheroids but the pearlite lamellarity >is not seen . In general hardness is in the range 120 - >150HB and the MOC is SA285 gradeC. But at different areas >hardness appears 90- 100HB. > >Please put some discussion light here, sirs. >regards

Debasis Main risk with packing is presence of pyraphoric iron. This compound doesn't need spark to ignite, only oxygen. This is particulate dangerous in refinery vacuum towers. Usually before opening for maintenance such column are chemically washed. Even after cleaning during maintenance it is good idea to keep packing wet. Good article: http://www.cheresources.com/ironfires.shtml About your failure you need to do some replica to evaluate the steel structures you got I agree with CVSRINIVASAN that Hardness values given seen do not seem to indicate any significant metallurgical transformation in the affected portions of the vessel to cause worry. Regards Luis Marques