Agenda Item: 653-209

Title: Additions to API 653 Appendix G To Enhance Performance Of Tank Bottom Examinations.

Date: 16th September 2007

Contact: Name: Jim Riley Company: Chevron Phone: 510- Email: [email protected] Others involved: Frank Furillo (ExxonMobil), Kelly Jones (ProInspect); Jim Johnston

Purpose: Improve and extend the guidance in Appendix G based on feedback from field inspections and examinations.

Source: Sub-Committee on Inspection

Impact: Non-Mandatory so minimal but does provide enhanced and useful field application guidance.

Proposal:

Draft of proposed new section to be added to API 653 Appendix G.

G.6 OWNER/OPERATOR FIELD CHECKS OF TANK BOTTOM EXAMINATIONS

G.6.1 Field audits by the owner/operator, the authorized inspection agency, or a third party that is independently employed from those performing the examinations, directly improve the field results of tank bottom examination. The practice of field audits is strongly recommended as an important way to reduce variability in results, improve performance of the examinations, and increase the accuracy of, and confidence in, the results in assessing the actual condition of the tank bottom.

G.6.1.1 The successful performance of tank bottom examination has several interdependent areas of best practice:

a. Personnel training and qualification, as well their familiarization and experience in using the particular type of equipment involved. b. The capabilities of the equipment and the cleanliness and first-rate mechanical condition of the equipment. c. The operating procedures used by the personnel that are specific to the job situation as well as the specific equipment involved. This includes verification and calibration of the equipment and the procedural practices of accomplishing the work.

G6.1.2 The list of potential items to check in Tables G.6.1 and G.6.2 is aimed at directly improving field results by focusing on the important aspects of best practices. The owner/operator or authorized inspection agency shall establish the content and level of field checks of tank bottom examinations. The list of things to check in the field is not intended to replace any established field audit procedures, but to supplement them as directed by the owner/operator or authorized inspection agency.

Table G.6.1 Focus Item Abbreviations: Abbreviation: Focus Area Description: E Equipment adequacy, cleanliness, mechanical condition, and functionality VC Verification and calibration OP Operating procedures JSC Job site cleanliness of tank bottom plate to be scanned SC Scope and coverage of tank bottom plate scanning work PT&Q Personnel training and qualifications

Table G.6.2 Potential Field Check Steps Focus Description of Potential Check Steps for Tank Bottom Examinations Areas PT&Q Verify the vendor records for training and qualification of tank bottom scanner operators and UT prove-up examiners. Verify that UT prove-up examiners are qualified by the API UT Tank Bottom Prove-up Examiner performance demonstration. OP Copies of the relevant written operating procedures are available at the job site. SC The scope and coverage of the tank bottom scanning is reviewed. The reporting format and content required is reviewed. E The equipment is mobilized in first-rate mechanical condition, clean and ready for use, and off-loaded without damage. VC A verification plate shall be available at the job site that matches the required plate thickness for the work scope, including applicability to coating simulation if the examination involves scanning through the coating. The owner/operator or authorized inspection agency may elect to test the tank bottom scanning operators and equipment using a blind test plate for the purpose of performance demonstration (may not be practical in all situations) prior to job-site verification and calibration. All final threshold adjustments must be completed inside the tank. E, VC The magnets and sensors are verified as being set to the proper height consistent with written procedures and OEM requirements. Magnets must be adjusted to accommodate plate warping (particularly important on plates thicker than 0.25-inch). Sensors are adjusted as low as possible for FRP/GRP liners. OP Each bottom plate being scanned is verified for nominal thickness using at least 1 UT reading. For lined tanks, the nominal and maximum thickness throughout the tank must be confirmed with a minimum of 1 DFT reading per plate area being scanned. JSC The tank bottom throughout the tank areas to be scanned is assessed for cleanliness and general condition of the plate product-side prior to scanning. VC, OP The examiner must readjust the equipment threshold setting to provide maximum gain consistent with the noise threshold on the actual tank bottom. VC, OP A 4-quadrant (including center and edge) soil-side search is conducted for a small volume pit with a depth approximately equal to the specified threshold to confirm the “calibration defect”. Then the scanner sensitivity must be readjusted so that it clearly indicates the presence of the “calibration defect”. The scanner sensitivity must be reconfirmed with the “calibration defect” (preferable) or verification plate at least once every 2 hours during scanning examinations to verify that the expected scanner indication has not changed. OP The scanning must be performed with specified amount of overlap (suggest at least 2 inches). OP Deformed tank bottom plates must be scanned from multiple directions. Deformed areas may require manual UT scanning. OP, PU The areas identified for UT prove-up should be less than that of a 3-inch circle and identified with highly visible markings. The UT operator should attempt to mark out the shape of larger flaws with chalk to differentiate between laminations and corrosion. PU All scanner indications must be identified and the cause recorded during the UT prove-up (includes false causes such as inclusions, welding arc strikes, areas of deformation and laminations). OP Scanners that require use of on-line data interpretation require highly skilled operators. Scanning set-up shall be checked before scanning is started, and then periodically checked during the scanning operation, by the overseeing qualified UT Level 2 examiner. E, OP The operator of the tank bottom scanning equipment must periodically inspect and clean the magnets and sensors and document the cleaning performed. OP The UT prove-up should be performed using an A-scan unit rather than a digital read-out instrument. The flaw detector should use a 5 MHz transducer and diameter in the range of 0.25 to 0.35 inch. In some cases, use of a B-scan unit may be required by the owner/operator if product- side conditions permit. OP Examination of the tank bottom plate near the shell or bottom welds is performed using an MFL edge scanner. Examination of the tank sump is included where applicable. The scanner operator must quantify and record the method of examination and extent of coverage/access to plate welds and shell-to-bottom welds. Document whether or not the inspection results were verified utilizing a second technique and whether it was random or 100%.

G6.1.3 The owner/operator or authorized inspection agency may elect to perform unannounced, periodic field audits to verify the job-site control by the vendor and that the best practices are being followed.