Luis Can you specifically inform at what depthand the length and width of lamination seen whether it is from internal surface or from external surface, and the correct length, depth and size of lamination detected in the first course shell plates (Lamination is a two dimensional linear defect). If the lamination seen is superficial lamination but located clsoe to or just 1 to 2 mm depth with length and breadth not wide spread from external surface to internal surface, then you may not have a major problem. If the laminationis superficial but located close to or just 1-2 mm depth and length and width of lamination not wide spread in each of the shell plates from internal surface, then you may have to consider factors to give additional support at the local lamination affected plates. Based on the info, you would like to share and the technique used to evaluate the lamination profile, the remaining wall thickness of the first shell course has to be worked out and then the tank's integrity to take the load stresses. Hope this helps C.V.Srinivasan Nishi Engineers Pvt Ltd India Nov 7, 2007 E-mail: nishi@vsnl.com >Dear Sirs, > >I have a question about aboveground storage tank integrity. >Following internal inspection was detected a couple of laps >(superficial laminations) in first shell. >Do you know if I have any suport code to study the >admissibility of concentration / deep of this type of >defects? API doesn't give us any information? > >Many thanks > >Luis

Luid/Debasis Lamination behavior under dynamic load stress and specifically under corrosive environment condition factors will vastly differ. It may or may need not remain dormant but may act as local stress raisers at the weakest points where lamination is sandwitched in the plates. Talking about specific case of atmospheric storage tank, lamination other than load bearing first shell course will be different in performance. This depends on the length, depth, size of lamination observed at the bottom first shell course plates, even in atmospheric tanks, under tensile load. If enough wall thickness is available either from inside or outside surfaces to take the load stress factors, discounting taking into account the length, depth, width of lamination observed in a specific plate and the areas where critical stress factors do not come into play, one can take comfort that lamination may not play important role in failure or in propagation of growth in a particular plate. Since API code constructed tanks have a good margin of safety factor, depending on the length, width and size of flaw sandwitched, one can assume that safety in operation may not be affected if left out but with monitoring done on performance. Although not related to atmospheric storage tank cases, we have had experience and have monitored carefully a critical vessel where lamination detected in time had an increasing trend to cause concern in safety of vessel operation. This was in a critical corrosive service and with medium pressure and medium temperature service in a fertilizer operating company. Failure is the ultimate which can become catastrophic also even in atmospheric storage tanks. One should not look at a problem from failure angle but from prediction and prevention aspects with timely detection and monitoring. Forum members who participate and express freely their independent views should consider aspects related to problems that can crop up in omissions to look at a problem. If individual members have limited exposure and experience, they can learn from the experience of other users. Hope this helps C.V.Srinivasan Nishi Engineers Pvt Ltd India Nov 8, 2007 E-mail: nishi@vsnl.com >with due respect to Mr. Srinivasan, in many Indian scenario >Lamination has been there as detected while UT thickness >gaging at mid-wall , aligned towards external or internal >sub-surface in various shell plates after commisioning >during periodic monitoring. It has been seen that for >Atmospheric Storage Tanks in diverse cases but usually not >taken as serious or fatal w.r.t. the continued operation of >the Tanks. This is because laminations are static defect and >does not grow so far it remain sub-surface and unoxidised. >And as it is principally 2D with very very little height it >rarely put any impact on redundancy of thickness. > >As a better safety measure reinforcement plate can be welded >but that need appropriate calculations and contour matching. > >If any one has any experince of tank Failure w.r.t. >lamination history kindly share pl. >regards >