The requirements for lining inspections are set forth in 49 CFR 180.407(f). The integrity of the lining on all lined CTs, when lining is required by this subchapter, must be verified at least once a year. Rubber (elastomeric lining) must be tested for holes. This test requires equipment that consists of:
- A high-frequency spark tester capable of producing sufficient voltage to ensure proper calibration.
- A probe with an L–shaped, 2.4-mm (0.09-inch) diameter wire with up to a 30.5-cm (12-inch) bottom wire leg (end bent to a 12.7-mm [0.5-inch] radius), or equally sensitive probe.
- A steel calibration coupon 30.5 by 30.5 cm (12 by 12 inches) covered with the same material and thickness as that to be tested. The material on the coupon shall have a test hole to the metal substrate made by puncturing the material with a 22-gauge hypodermic needle or comparable piercing tool.
Begin the test by calibrating the probe. The probe must be passed over the surface of the calibration coupon in a constant, uninterrupted manner until the hole is found. The hole is detected by the white light or light blue spark formed. A sound lining causes a dark blue or purple spark. The voltage must be adjusted to the lowest setting that will produce a minimum 12.7-mm (0.5-inch) spark measured from the top of the lining to the probe. To assure that the setting on the probe has not changed, the spark tester must be calibrated periodically using the test calibration coupon and the same power source, probe, and cable length.
After calibration, the probe must be passed over the lining in an uninterrupted stroke. Holes that are found must be repaired using equipment and procedures prescribed by the lining manufacturer or lining installer. Linings made of anything other than rubber (elastomeric material) must be tested using equipment and procedures prescribed by the lining manufacturer or lining installer.
Results of the inspection must be recorded and include any defects discovered and steps taken to remedy the defect. Degraded or defective areas of the CT liner must be removed, and the CT wall below the defect must be inspected. Corroded areas of the tank wall must be thickness tested.
Defects in the integrity of corrosion-resistant rubber, polymer, and similar linings are detected by visual examination and by high-frequency spark-testing equipment. Procedures for performing this testing and repair must be written using the lining manufacturer’s instructions. Personnel performing the testing and repair must be trained in the procedures and equipment used. Personnel qualifications must be certified by the employer.
Voids detected during inspection require removal of the lining at the defect and surrounding area and an inspection of the tank shell for corrosion and remaining metal thickness. Welded repairs must be accomplished in accordance with the requirements of the NBIC. The elastomeric lining must then be repaired and re-examined.
