Holiday Detection

Holiday detection finds, electrically, pinholes, thin spots and discontinuities in an insulating protective coating. A voltage is applied to the coating surface; at a discontinuity the current reaches the metal and the instrument gives an audible or visual alarm.

The aim is to find, before the item enters service, the discontinuities that defeat the corrosion protection of the coating. A single millimetre-sized hole reduces the protective effect of the whole coating system to zero at that point and starts accelerated corrosion.

• External pipeline coatings
• Storage tank interior and exterior coatings
• Ship and marine structure paints
• Concrete protective coatings
• Chemically resistant linings

NDT has no interval of its own; how often it is applied follows the inspection programme it serves. In manufacturing the governing factor is the coverage required by the product standard and the specification (e.g. a given percentage of welds); in operation it is the asset integrity or risk-based inspection programme.

• Invisible pinholes in the coating
• Thin coating areas
• Coating continuity at weld seams and corners
• Coating integrity at repair areas
• Assessment together with coating thickness

• ISO/IEC 17020
• ASTM D5162
• ASTM G62
• NACE SP0188
• ISO 2746
• ISO 29601

• Low-voltage (wet sponge) holiday detector
• High-voltage (spark) holiday detector
• Coating-thickness gauge
• Calibration and verification rig
• Earthing connection equipment

1. 1Selection of Method and TechniqueThe type and location of the discontinuity sought and the material properties are assessed to select a suitable method and technique; a written procedure is prepared.
2. 2Verification of Personnel and EquipmentThe level and industrial-sector qualification of the operator under EN ISO 9712 and the calibration records of the equipment are checked.
3. 3Surface PreparationThe inspection surface is prepared as the method requires; coating, rust and contamination directly affect the sensitivity of the method.
4. 4Calibration and Sensitivity VerificationA reference block or control specimen is used to demonstrate that the system can detect the discontinuity sought.
5. 5Performing the InspectionScanning is carried out according to the procedure; indications are recorded and located.
6. 6AssessmentIndications are evaluated against the applicable acceptance standard to determine whether they are defects; they are sized.
7. 7ReportingMethod, technique, equipment, calibration, findings and acceptance criteria are reported together.

Every discontinuity found is marked, recorded and repaired according to the coating specification. After repair, the area is retested. The acceptance criterion is usually 'no discontinuity found'.

• The inspection body and the personnel's EN ISO 9712 level and sector
• Method and technique applied and the written procedure number
• Part and weld examined, with a location sketch
• Equipment, consumables and calibration records
• Surface condition and inspection conditions
• Indications recorded, with their location and size
• Acceptance standard applied and the result of the evaluation
• Accept / reject decision

Non-destructive testing is carried out as an accredited inspection activity under ISO/IEC 17020. The second decisive factor in NDT is personnel qualification: the operator must be certified under EN ISO 9712 for the method, level and industrial sector concerned. An examination performed with a method outside the scope of that certificate is not valid. EUROLAB holds internationally recognised accreditation under ISO/IEC 17020, granted by accreditation bodies that are signatories to the ILAC mutual recognition arrangement.

• VT Visual
• PT Penetrant
• MT Magnetic Particle
• UT Ultrasonic
• RT Radiographic
• ET Eddy Current
• PAUT
• TOFD