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r? <br />r? <br />5.6 Described below is the visual testing procedure. If corrosion and pitting is <br />found, determine the minimum remaining wall thickness. <br />5.6.1 Do not enter a tank until you have determined that a breathable, <br />non-explosive atmosphere exists within the tank. Follow OSHA <br />requirements for confined space entry and see NFPA 326, <br />"Standard for the Safeguarding of Tanks and Containers for Entry, <br />Cleaning or Repair." <br />5.6.2 Use sufficient light to illuminate the interior of the tank. <br />5.6.3 Check for the presence of water, excessive corrosion, and other <br />forms of deterioration. <br />5.6.3.1 Measure the extent and depth of any pitting found. <br />5.6.3.2 Inspect all welds. <br />5.6.3.3 Determine the extent of general corrosion. <br />5.6.4 Consider the construction of lap joints in all inspections. Lap joints <br />which allow water to accumulate may lead to accelerated corrosion <br />and therefore require special attention during inspections. <br />6.0 CERTIFIED TANK INSPECTION CRITERIA <br />6.1 After the minimum remaining wall thickness is determined in paragraph 5, <br />apply the following criteria to determine if the tank may remain in service: <br />6.1.1 If less than 5% of any 12 inch by 12 inch square area of the tank <br />has a remaining wall thickness less than or equal to 50% of the <br />original thickness, remove the tank from service and contact a <br />qualified tank manufacturer to have these sections repaired. Bring <br />the thickness of these areas back to the original design thickness. <br />Have the qualified inspector re-inspect the tank after the repairs <br />have been made. Identify and correct the cause of corrosion. <br />Re-inspect the tank in 5 years, or less as recommended by the <br />qualified tank inspector. <br />6.1.2 If more than 5% of any 12 inch by 12 inch square area of the tank <br />has a remaining wall thickness less than or equal to 50% of the <br />original thickness, remove the tank from service and contact a <br />qualified tank manufacturer to have these sections repaired. These <br />sections must be repaired by cutting out these sections and <br />replacing them with new steel of the original design thickness or <br />else by welding new steel of the original design thickness over the <br />damaged areas. These repairs must be made from the side that is <br />corroded. Have the qualified inspector re-inspect the tank after the <br />repairs have been made. Identify and correct the cause of <br />corrosion. Re-inspect the tank in 5 years, or less as recommended <br />by the qualified tank inspector. <br />6.1.3 If the remaining wall thickness is more than or equal to 50% but <br />less than 75% of the original thickness, identify and correct the <br />cause of corrosion. Re-inspect the tank in 5 years, or less as <br />0 AST Inspection Standard 7 <br />September 2000