Laserfiche WebLink
Appendix 2 - Ultrasonic Thickness Gauging Procedure <br /> A2.1 Scope <br /> A2.1.1 This Appendix prescribes minimum requirements for internal inspection and assessment <br /> of installed underground storage tanks by ultrasonic thickness gauging.In general,it prescribes personnel <br /> certification requirements, test equipment capabilities, tank interior surface preparation, gauging <br /> procedures, minimum acceptable grid patterns for ultrasonic thickness gauging, tank inspection report <br /> requirements, and pass/fail criteria. <br /> A2.2 Personnel Qualifications: <br /> A2.2.1 Personnel qualified for ultrasonic thickness gauging of underground storage tanks shall be <br /> trained and certified to Nondestructive Testing, Level 1 Competence in accordance with the guidelines <br /> specified by the American Society for Nondestructive Testing, Recommended Practice No. SNT-TC-1 A, <br /> Personnel Qualification and Certification in Nondestructive Testing. Qualification requirements shall be <br /> limited to ultrasonic thickness gauging. <br /> A2.2.2 Qualified personnel shall be responsible for conducting ultrasonic thickness gauging, data <br /> interpretation, and evaluation. <br /> A2.2.3 The employer shall establish and maintain a written procedure for administration of <br /> training, examination and certification of nondestructive testing personnel. <br /> A2.3 Equipment Capability Guideline: <br /> Equipment used for gauging shall meet the following minimum requirements: <br /> Measurement range: .050 inches to 2 inches <br /> Resolution: .002 inches minimum <br /> A2.4 Surface Preparation <br /> After the tank has been emptied, the interior tank surfaces shall be cleaned as required for the use of <br /> ultrasonic thickness gauging equipment. <br /> A2.5 Gauging Objective: <br /> The objective of thickness gauging is to assure the average tank shell thickness is greater than 75%of the <br /> original shell metal thickness through a series of identified,averaged measurements or three-foot by three- <br /> foot quadrants;one-foot by one-foot subdivisions of quadrants;perforations;and thin metal target areas. <br /> A2.6 Original Shell Metal Thickness: <br /> Original shell metal thickness shall be established by gauge measurements taken at the tank top man- <br /> way. <br /> A2.7 Ultrasonic Thickness Gauging Procedure: <br /> A2.7.1 Control Quadrants:For gauging measurement control,tank walls shall be divided into quadrants <br /> as follows: <br /> a) Walls:Measurements for tank walls shall be divided into three-foot by three-foot quadrants <br /> beginning at the fill end of the bottom of the tank and extending outward around the tank <br /> circumference and along the tank length.Any additional area of the tank wall which is less <br /> than three-feet by three-feet shall be measured and treated as additional quadrants.(See <br /> Figure A2.1). <br /> 2/99 <br /> Page 24 of 30 <br />