Hi Kerosene tank had been leaked after two years in services. Inspection was done and revealed that three pin hole leaks under by side corrosion .The tank foundation is asphalt and had been dissolved by keorsene. Tank history showed during T&I 2003 two pin hole leaks were patched and kerosene product already contaminated under the tank foundation and it is the main cause for the failure at 2005. Now the tank foundation is dissolved and the tank bottom had metal loss 40-50% at all plates also, three pin hole leaks. In regard to that it recommended to reproflie the asphalt foundation and patch all plates that had metal losses or replace all the bottom plate major replace . Your input will be valued.

Further to my earlier response I thought to share few more things. (1) Bottom plate ( except critical zone area) is essentialy a membrane and there exist little stress. Thus under practical consideration , it may be allowed to loose approx. 60% - 80% of its design thickness because of corrosion before repairs are required. (2) 100% bottom plate critical scanning reqd. and it has to be certified as"no pinhole leak or no about to leak condition". (3) But the concern is if again any leak happens the asphalt will be dissolved in time. So pl. think about some suitable alternate to conventional asphalt/bitumen . You may discuss the matter with your API 650 Tank Designer or API 653 Tank Inspector to evaluate out the merit in using COAL TAR Bed matrix as good coal tar has little solubility in Petrol, Kerosene, I believe. Also you may think about use of some non-biodegradable polymeric plastic bed liner at bottom plate soil side of suitable thickness slurry mixed with fine sand and compacted. In case you do get any alternate solution pl. also share with me. regards Debasis.Mitra@hpl.co.in HALDIA PETROCHEMICALS LIMITED ; West Bengal : INDIA Mobile : 94342 36119

Dear Mark Mor, I went thru' your letter as well as the replies. Would you please clarify some of my doubts ? The tank had two pinhole leaks in 2003 T&I. Whether these were due to corrosion from product side or underside of the plates ? Were there substantial corrosion from product side ? Did you do "coupon cutting" of bottom plates at few locations to check the condition of underside ? Whether any pneumatic testing was done to ascertain leaktightness of bottom plates ? Regarding your queries, it is prudent to go for complete replacement of bottom plates alongwith replacement of degraded foundation. Regarding patch welding of bottom plates - please don't do it. Our experience in similar plate overlaying of bottom plates is very poor. By the way, what is the time interval between two tank T&I in your place ? One more thing - tank foundation are designed, among other things, to reduce underside corrosion. Are they designed to withstand dissolution by the product ? In that case we will see different criteria for different product, won't we? Regards