Hi Experts, Our plant is having knock out drum which are not internally inspeted for date of commisioning(9 years).We have measured the thickness survey on th shel plate ,nozzles and dish end.No thickness reduction observed. But we are concerened about the area of plate below the RF pad of nozzle.Here we are suspection some Stress Corrosion Cracking.Also thickness survey is not possible in this area due to gap betwwen RF pad and shell plate. I would like to know any of you have done any NDT method to assure the integrity of this portion?Please suggest us with any advanced NDT method which can be carried out.

Inspector 1978 From SCC detection, main vessels in the system would not be an exception and would show symptoms even before K.O drum problem is identified by NDT tests. When you have access to inspect the main vessel - LPG Or Propane or Butane etc., and the main vessel had not shown any deterioration or had not shown any symptom of SCC from N.D.T tests, K.O. Drum shell plates will not be an exception from SCC inspite of the fact that K.O drum internals are not accessible for a thorough inspection from inside. However, K.O drum external UT flaw of welds is possible to detect SCC problem- if any. From detection of SCC, thickness test or thickness reduction will not show. If you suspect SCC only in the area around nozzle holes with R.F pad provision given in K.O drum, symptoms of SCC and subsequent crack in the shell plate below the RF pad area would definitely show thru' tell-tale holes provided in R.F pad. For detection of SCC, you can do UT Flaw check of the main welds in K.O drum also. If this does not show then you have to assume that the RF pad area had not been affected due to SCC. If it is pitting due to low pH and high H2S in the system, main vessel will not be an exception to this trend also. Main vessel would be affected due to pitting trend than K.O drum internals. Hope this helps you C.V.Srinivasan Nishi Engineers Pvt Ltd India Dec 14, 2009 E-mail: nishi@vsnl.com >Hi Experts, > > Our plant is having knock out drum which are not >internally inspeted for date of commisioning(9 years).We >have measured the thickness survey on th shel plate ,nozzles >and dish end.No thickness reduction observed. > >But we are concerened about the area of plate below the RF >pad of nozzle.Here we are suspection some Stress Corrosion >Cracking.Also thickness survey is not possible in this area >due to gap betwwen RF pad and shell plate. > > >I would like to know any of you have done any NDT method to >assure the integrity of this portion?Please suggest us with >any advanced NDT method which can be carried out.