DEAR lIMA As we don't have any such tell-tale systems for our tanks, I am quite ignorant about this issue. H2S ACTIVATE THE HCL REACTION TO DESTROY THE CARBON STELL. Really In the CUI I am not hear any new method to inspect the CUI as I am corrosion Engineer in the inspection unit we use the UT reading on the location and I advise them to use the Through screen to avoid the CUI. And also, there were locations the insulation not needed so we remove the insulation for ever. So try to use the through screen to see the condition. If we want to know the corrosion and CUI I will sent you a document discuss the CUI deeply. Thanks Mark Mor Corrosion engineer /Inspection Unit

Lima CUI - in marine (coastal areas) atmosphere is a known problem. Real time RT will not help - as it is as laborious and as expensive as removal of insulation and provide new insulation. Other method - ET is also ineffective for CUI corrosion condition detection. One effective way of ensuring evaluating the condition of C.S pipe or plate material under CUI is to cut windows - depending on the wind drection that has prevailed at your area - and estimate by both UT thickness profile of cut window areas of CUI and also localized RT of the same. Selected location of cut windows and UT / RT profile monitoring in a periodic way will give the corrosion profile of the equipment or piping. For the next periodic inspetion, monitor again the worst affected area of the first inspection and choose some more selected area of cut window of CUI areas in the same equipment and piping. A progressive record of such monitoring over a two year peiod will give enough data to know the pattern, location of severe or moderate and extent of pitting and other surface attack on C.S , the depth of corrosion under insulation and the extent of external replacement criteria for the same equipment / piping in your coastal refinery. We did a similar CUI for a marine (coastal) piping operating under sub-zero conditions for a period of 2 years and established the pattern of corrosion, extent and severity of pitting. direction of wind affecting CUI in steel material . This included under-ground piping. Over a period of 2-3 years of periodic monitoring by simple UT thicknes and selective RT of some locations, prepared planning for replacement of a cross-country pipeline of 5-6 km was done effectively in a coastal area in severe CUI conditions for above ground and under ground pipelines . To my mind, this simple testing tools like UT thickness, pit depth gauge, RT at selected areas, DP at selected welds appear to be the best inspection tool and inspection strategy to monitor and determine the severity and extent of degration under CUI for a refinery piping and equipment in coastal areas. We have done this progressive evaluation using such simple NDT technicques for a client in coastal belt in India . We, as a consulatant, have been quite successful in predicting the rate of deterioration and in pre-determining the areas and effetively plan for replacement for the severely affected portions in a cross-country pipeline at sub zero condtions of - 32 deg centigrade where the severity is much worse combined with marine atmosphere and the prevalent conditions of dust and boiler and furnace stack emissions from nearby plants (externally afffected or degraded areas under CUI). Trust this is of some help to you C.V.Srinivasan Nishi Engineers Pvt Ltd Chennai India June 20 E-mail:nishi@vsnl.com >CUI is a problem in our case also. > >Let's see. Among many refineries we operate, we have one >of the oldest refineries (estd in year 1901). Except that >refinery, our other refineries are 30-45 years old. > >CUI is problem here too, especially due to very high >rainfall & in our coastal refinerues. We have discussed in >some of the NACE corrosion meets and with some well known >experts in the field. The answer we finally get is to"remove >insulation - inspect". In our case manual labor is cheap >and we can afford to do so. > >Even then we try to segregate the high risk and low risk >category. Above, say 180 C, CUI is less likely. Betwen >150-180 C, some CUI. Between 130-150 C, moderate to severe. >Below 130 C, it is too severe. Wherever possible (if our >energy conservation group allows it), we try to remove >insulation permanently. > >My idea is, identify eqpt as per service category and temp. >category. Remove insulation and inspect. While >re-insulating, take steps to reduce CUI. Anyway, any >decision will ultimately depend on local socio-economic >condition. > >'Hope it helps > >Regards