Luis Antonio Segregations and Laminations in your storage tank is present since inception - 1967. You have not explained the size of segregations, lamination length and width. Segregations may not play any harmful problems unless there is a possibility of linkage of the segregations. Yes the plate thickness at laminated locations will be varying from a minimum of 16 mm (for a 4 mm thickness lamination from inside of the tank plate) and would be 4 mm (for a 16 mm thick lamination from inside of the tank plate). If the length of laminated locations and the thickness at the worst measured is 16 mm, the first shell course would be close to discard for an atmospheric tank storing gasolene. If the laminated location thickness is mostly in the range of 4 mm - 6 mm from inside, you still have sufficient thickness of 14-16 mm out of 20 mm thickness. This may not give any major problem to store gasolene. You have to take a profile mapping using A scan or regular UT thickness at the first shell course plates to ascertain if this lamination is restricted to one heat of a plate or it is distributed widely in some other plates of the bottom first shell course. From the profile mapping of lamination and segregations you will get the lowest thickness and also the highest thickness in each segment plate of first shell course. One approach would be to consider and provide reinforcement from outside for the first shell course with another 10-12 mm so that effective thickness remains around 20-24 mm taking the old laminated plate and the new strength giving additional first shell course plate from outside. This will no doubt affect the aesthetic appearance of the tank. Ultimtely, from safety consideration this will be faster, easier and less time consuming and will additional safety to the tank bottom shell course even for the worst case of 16 mm is affected due to lamination from inside out of the original thickness 20 mm. Segregations - even if it MnS inclusions, Al2O3, Fe-Si inclusions, Phosporus inclusions will not affect. Trust this will help you to do another survey to take a complete profile mapping of each and every affected plate with lamination / segrgations (this should give the exact width, orientation, length of each lamination seen and also the depth from inside of the plate). C.V.Srinivasan Nishi Engineers Pvt Ltd India Dec 6, 2006 E-mail: nishi@vsnl.com >Good morning!!! > >I'm storage tank inspector and I would like help to discuss >a problem about segregations and laminations in one first >shell plate. > >The tank already is very old (1967) isolated to storage fuel >oil. Now he it's storage gasoil. > >Following a out of service inspection (during this week) e >detected in one first shell plate (after inside A-Scan >control) that all plate contain segregation between 4mm and >16 mm (nominal thickness is 20 mm). > >I would like know, according with tank records (any remarks >during in-service since 1967) what it your opinion about >this case, because according API 653 we can't permit this >situation. > >What kind of END (as alternative) you sugere? >Must we replace the plate? >I will appreciate a answer as soon as possible. >Thanks in advance > >Luis Ant%C3%B3nio

Luis Antonio Segregations and inclusions in plates or rolled pipes would not give any major problem for your tank. A similar problem was observed by us in many column leg supports for a sphere (1500 MT capacity) which takes both axial and hoop load sresses. Since this was observed in column leg supports, additional reinforcement was given in leg supports. This has strengthened the weak areas and no problem is expected. I agree mapping is a laborious problem. One approach would be to restrict profile mapping to ASTM A 432 or better still to DIN Standard of 1972. DIN standard or BS specifies a grid profile mapping using a smaller head probe much closer than ASTM A 432 grid profile mapping. ASTM specifies a probe head of 25 mm. whereas DIN or BS specifies smaller probe head of even 10 mm. From the description of your problem, it appears to me, you do not have to unduly worry on your first shell course plates even though you might have isolated spots with lower thickness of 4 mm (due to 16 mm spot location of segregation or local lamination). Also this is a static vessel under atmospheric pressure conditions inspite of handling gasolene. If you are prepared to sacrifice aesthetic appearance of the outer of the tank, reinforce those local spot ares with patch plates from outside to take care of the small varitaitons in drop in thickness due to segregations or local laminations. This should solve your problem Trust this will help you to map more accurately and re-inforce the widely affected areas with a 10 mm or 12 mm plate addition from outside. For small areas with variations in thickness you can ignore. C.V.Srinivasan Nishi Engineers pvt Ltd India Dec 7, 2006 E-mail:nishi@vsnl.com >Dear Sir, >In first place I would like thanks. >Really we try to take a profile mapping using A Scan >(according with EN10160) from tank inside (20 000 m3 >capacity). >When we started with A Scan, we got a couple of screen >picks, resulting from a couple of indications (segregations) >in all parts of the plate. We firstly defined a grid and >after a "spot" areas and the signal always was the same ==> >mainly segregations mix with small laminations at different >deeps. Was completely impossible for us mapping indications >because in any "spot" area the display scan values jump >between 4 and 16 mm (like a cruise signal) in deep with >reflectors between 2 and infinite. Was completely impossible >get the segregation / lamination orientation with A scan. >Really We don%E2%80™t know what kind of discontinuities we have >inside, but we suppose have segregation inside which could >be linkage at differents depps. >The worst situation was 16 mm eco from inside (remaining 4 >mm in wall thickness). > >I hope hear news from you. > >Many Thanks. > >Luis > > > > > >>Luis Antonio >> >>Segregations and Laminations in your storage tank is present >>since inception - 1967. >> >>You have not explained the size of segregations, lamination >>length and width. >>Segregations may not play any harmful problems unless there >>is a possibility of linkage of the segregations. >> >>Yes the plate thickness at laminated locations will be >>varying from a minimum of 16 mm (for a 4 mm thickness >>lamination from inside of the tank plate) and would be 4 mm >>(for a 16 mm thick lamination from inside of the tank >>plate). >> >>If the length of laminated locations and the thickness at >>the worst measured is 16 mm, the first shell course would be >>close to discard for an atmospheric tank storing gasolene. >> >>If the laminated location thickness is mostly in the range >>of 4 mm - 6 mm from inside, you still have sufficient >>thickness of 14-16 mm out of 20 mm thickness. This may not >>give any major problem to store gasolene. >> >>You have to take a profile mapping using A scan or regular >>UT thickness at the first shell course plates to ascertain >>if this lamination is restricted to one heat of a plate or >>it is distributed widely in some other plates of the bottom >>first shell course. >> >>From the profile mapping of lamination and segregations you >>will get the lowest thickness and also the highest thickness >>in each segment plate of first shell course. >> >>One approach would be to consider and provide reinforcement >>from outside for the first shell course with another 10-12 >>mm so that effective thickness remains around 20-24 mm >>taking the old laminated plate and the new strength giving >>additional first shell course plate from outside. >> >>This will no doubt affect the aesthetic appearance of the >>tank. Ultimtely, from safety consideration this will be >>faster, easier and less time consuming and will additional >>safety to the tank bottom shell course even for the worst >>case of 16 mm is affected due to lamination from inside out >>of the original thickness 20 mm. >> >>Segregations - even if it MnS inclusions, Al2O3, Fe-Si >>inclusions, Phosporus inclusions will not affect. >> >>Trust this will help you to do another survey to take a >>complete profile mapping of each and every affected plate >>with lamination / segrgations (this should give the exact >>width, orientation, length of each lamination seen and also >>the depth from inside of the plate). >> >>C.V.Srinivasan Nishi Engineers Pvt Ltd India Dec 6, 2006 >>E-mail: nishi@vsnl.com >>>Good morning!!! >>> >>>I'm storage tank inspector and I would like help to discuss >>>a problem about segregations and laminations in one first >>>shell plate. >>> >>>The tank already is very old (1967) isolated to storage fuel >>>oil. Now he it's storage gasoil. >>> >>>Following a out of service inspection (during this week) e >>>detected in one first shell plate (after inside A-Scan >>>control) that all plate contain segregation between 4mm and >>>16 mm (nominal thickness is 20 mm). >>> >>>I would like know, according with tank records (any remarks >>>during in-service since 1967) what it your opinion about >>>this case, because according API 653 we can't permit this >>>situation. >>> >>>What kind of END (as alternative) you sugere? >>>Must we replace the plate? >>>I will appreciate a answer as soon as possible. >>>Thanks in advance >>> >>>Luis Ant%C3%B3nio