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may be required. Personnel performing this procedure shall be trained and certified in Non-Destructive <br /> Testing,Level 1 as specified by the American Society for Non-Destructive Testing,Recommended Practice <br /> SNT-TC-1 A or equivalent.See Appendix 2 for ultrasonic thickness gauging procedures. <br /> 2.3.4 Various criteria are used to determine whether a tank qualifies for internal lining. Making the <br /> determination requires assessment of the structural soundness of the tank,which may be accomplished by <br /> visually inspecting the tank for quantity and size of perforations in its walls. <br /> 2.3.5 Guidelines to be used in determining whether a tank should be lined are: <br /> a) Perforations no larger than 1-Y2'in diameter,and under the gauge opening,no larger than <br /> 2-1/2'in diameter. <br /> b) Less than five (5) perforations (none exceeding 1/2'in diameter in any one (1) square foot <br /> area). <br /> c) Less than twenty(20) perforations (none exceeding 1/2"in diameter)in a five hundred (500) <br /> square foot area. <br /> 2.3.6 Perforations to be repaired must be reamed until the metal thickness at the edges of the hole is a <br /> minimum of 1/8". <br /> 2.3.7 Tanks exceeding any of the above criteria may not be internally lined unless approved by an <br /> authority having jurisdiction. Tanks meeting the above criteria would be deemed suitable for a minimum <br /> of ten (10) years life extension by lining with EnvirolineTM 1250. <br /> 2.4 Tank Repairs <br /> 2.4.1 To permanently repair perforations and split seams,either weld and/or seal the perforated area <br /> with a reinforced epoxy laminate patch. <br /> 2.4.2 Weld Repairs <br /> a) Plates may be welded over perforated areas of the interior tank walls so as to comply with <br /> the perforated criteria specified in 2.3.5.Welding may also be used to repair breaks or splits <br /> in the seams. <br /> b) Welding operations must be performed after abrasive blasting the tank to white metal. If <br /> welding is needed on a lined tank, the lining should be removed a minimum of six (6) <br /> inches in all directions from the area to be welded. <br /> c) Continue to test for flammable vapor and oxygen concentrations throughout the entire <br /> welding operation. Monitor vapors within three (3) feet of where the welding is being <br /> performed. <br /> d) All personnel within the tank must wear respiratory protection. Use an exhaust hood to <br /> control fumes generated during welding.Place hood within twelve(12)inches of the area <br /> being welded, and maintain a minimum velocity of 200 cubic feet per minute to remove <br /> all smoke,vapors and flammable substances generated during the welding operation.In <br /> addition, use an eductor to provide continuous ventilation in accordance with 2.1.8(b). <br /> e) The use of welding to repair perforations must be by continuous welding of the steel plate <br /> edges to the existing tank wall. Plates must overlap perforation(s) by at least one (1) inch. <br /> Steel plates used for weld repairs must be equal to or greater than the original tank metal <br /> thickness, and match the contour of the tank wall. <br /> 2/99 <br /> Page 9 of 30 <br />