Holiday Detection Dispute on a Buried Pipeline Coating
A buried steel pipeline is coated with a fusion-bonded epoxy at 400 µm. The inspector runs a high-voltage holiday detector at a test voltage the contractor set 'by feel.' Several holidays are found near field joints where the coating was patched. The contractor argues the holidays are false readings caused by too high a voltage and wants to skip repair. The specification requires holiday testing at a voltage based on coating thickness and requires repair of all holidays. Ambient conditions are dry and the coating is fully cured.
1. How would you determine whether the holiday indications are real or artifacts of test voltage?
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Establish the correct test voltage from the specification or the coating manufacturer's guidance, which is typically based on coating thickness (higher thickness needs higher voltage to detect defects, but excessive voltage can perforate sound coating and create false indications). Set the detector to that voltage, verify the equipment is functioning and the electrode is in good contact, and re-test the suspect areas at the correct setting.
Re-test the same spots and nearby sound coating. If indications persist at the correct voltage and are localized at the patched field joints, they are likely real defects (pinholes, thin spots, or patch edges). If indications disappear at the correct voltage and only appear at excessive voltage, they were artifacts. Either way, the decision must be based on a controlled re-test at the specified voltage, not on 'by feel' settings.
2. Assuming some holidays are real, what repair and verification would you require, and how would you document the disposition?
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Repair: mark each confirmed holiday, remove the defective coating locally to sound material, clean and prepare the area per the coating system's repair procedure, and re-apply the compatible patch to the specified thickness. Allow cure, then re-test the repaired area at the correct voltage to confirm no holiday remains. Verify patch thickness and adhesion where applicable.
Documentation: record the test voltage used, equipment calibration/verification, location of each holiday, repair method and materials, re-test results, and the final disposition (repaired and accepted). Note the initial 'by feel' voltage as a nonconformance and the corrective action. The contractor's request to skip repair is not acceptable where the specification requires repair of all holidays.