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0 1 0 MI6.2 SECTION GAUGING - Thickness The percentage of original tank metal thickness gauging measurements shall be taken at the shall be determined by dividing the tank's center of each section in the tank wall and present average tank metal thickness (as heads. Thickness readings of 75 percent or less computed in figure 132) by the original tank of the original tank metal thickness shall metal thickness. require further gauging as described in thin wall target area gauging. Thickness readings greater than 75 percent of the original tank metal MI7.3 THICKNESS GAUGING REPORTS thickness shall be recorded on Report Form A contained in Chapter B as the measurement for the section (See Figure B2, Part 1 and 2 of MI7.3.1 Thickness gauge measurements shall Chapter B). be recorded on an ultrasonic thickness gauging report(See Figures B2 and B3 in Chapter B). MI6.3 THIN-WALL TARGET AREA Any M17.3.2 The thickness gauging reports in section with a thickness gauge measurement of figures B2 and B3 of Chapter B shall be 75 percent or less of the original tank metal provided to the tank owner. These reports shall thickness shall be subdivided into 9 subsections be maintained by the owner and the person with the gauge readings of the 9 subsections performing the test. Alternate report forms recorded on Report Form B (see figure 133). maybe utilized provided the alternate report Each subsection shall have a thickness reading forms contain all the information outlined in at the center of each subsection. The average of figures B2 and B3. the nine subsection readings shall be recorded as the tank metal thickness measurement of the section. If the average of the 9 gauge reading MI8.0 PASS/FAIL CRITERIA measurements is less than 75 percent of the original tank metal thickness, that section may be repaired in accordance with Chapter A, MI8.1 The average tank metal thickness shall Section A10.4.5. All repairs to thin wall target be at least 75% of the original tank metal areas shall be performed prior to final gauging thickness; and, the average tank metal thickness measurements. of a section which was designated as a thin wall target area shall be at least 75% of the original tank metal thickness to pass. MI7.0 AVERAGE TANK METAL MI8.2 Tanks not meeting the wall thickness THICKNESS requirements of section 8.1 shall be failed and shall be closed in accordance with applicable MI7.1 Average tank metal thickness shall be local,state,and federal regulations. determined by averaging all the section gauge measurements using the computation contained MI9.0 OPERATIONAL LIFE in Figure B2 of Chapter B. MI9.1 If the average tank metal thickness is MI7.2 PERCENTAGE OF ORIGINAL TANK determined to be 75 percent to 85 percent of the METAL THICKNESS original tank metal thickness,a cathodic 6