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9 0 <br /> B7.5.1.1 WALLS - The tank cylinder wall shall be A10.4.5.All repairs to thin wall target areas shall be <br /> divided into three-foot by three-foot sections beginning at performed prior to final gauging measurements. <br /> one of the tank's ends at the bottom and extending <br /> vertically around the tank circumference and horizontally B7.5.2 AVERAGE TANK METAL THICKNESS <br /> along the tank's cylindrical length. Any additional area of <br /> the tank's cylindrical sections which are less than three Average tank metal thickness shall be determined by <br /> feet by three feet shall be designated as additional averaging all the section gauge measurements using the <br /> computation contained in Figure B2. <br /> sections (See Figure B 1). <br /> B7.5.3 PERCENTAGE OF ORIGINAL TANK METAL <br /> B7.5.1.2 HEADS - Tank end caps (heads) shall be THICKNESS <br /> divided into four equal quadrants by extending The percentage of original tank metal thickness shall be <br /> horizontally and vertically from the center of the end cap. determined by dividing the tank's present average tank <br /> Each quadrant shall be divided into three-foot by three- metal thickness (as computed in figure 132)by the original <br /> foot sections beginning at the center of the tank head and tank metal thickness. <br /> extending vertically and horizontally toward the tank <br /> walls. Any additional areas of the tank heads which are <br /> less than 3 foot by 3 foot shall be designated as additional B7.6 THICKNESS GAUGING REPORTS <br /> sections(see figure B2,Part 2). <br /> B7.6.1 Thickness gauge measurements shall be recorded <br /> on an ultrasonic thickness gauging report (See Figures <br /> B7.5.1.3 SECTION GAUGING - Thickness gauging B2 and 133). <br /> measurements shall be taken at the center of each section <br /> in the tank wall and heads. Thickness readings of 75 B7.6.2 The thickness gauging reports in figures B2 and <br /> percent or less of the original tank metal thickness shall B3 shall be provided to the tank owner. These reports <br /> require further gauging as described in thin wall target shall be maintained by the owner and the person <br /> area gauging. Thickness readings greater than 75 percent performing the test. Alternate report forms maybe utilized <br /> of the original tank metal thickness shall be recorded on provided the alternate report forms contain all the <br /> Report Form A as the measurement for the section (See information outlined in figures B2 and B3. <br /> Figure B2,Part 1 and 2). <br /> B8.0 PASS/FAIL CRITERIA <br /> B7.5.1.4 THIN-WALL TARGET AREA Any section B8.1 The average tank metal thickness shall be at least <br /> with a thickness gauge measurement of 75 percent or less 75% of the original tank metal thickness; and, the average <br /> of the original tank metal thickness shall be subdivided tank metal thickness of a section which was designated as <br /> into 9 subsections with the gauge readings of the 9 a thin wall target area shall be at least 75% of the original <br /> subsections recorded on Report Form B (see figure B3). tank metal thickness to pass. <br /> Each subsection shall have a thickness reading at the <br /> center of each subsection. The average of the nine <br /> subsection readings shall be recorded as the tank metal <br /> thickness measurement of the section. If the average of B8.2 Tanks not meeting the wall thickness requirements <br /> the 9 gauge reading measurements is less than 75 percent of section 8.1 failed and shall be closed in accordance <br /> of the original tank metal thickness, that section may be with applicable local,state,and federal regulations. <br /> repaired in accordance with Chapter A,Section <br /> 47 <br />