NACE SP-0188-Holiday testing of internal lining.
Equipment-The holiday testing equipment shall be used as high voltage spark tester for coating thickness above 500microns (20mills) ASTM SP D0188.The equipment should be battery operated type and metal brush shall be capable of scanning the tank coating.
Calibration of holiday equipment-The holiday detector shall be calibrated once in every 6 months.The tester shall be tested for sensitivity prior to initial use and periodically thereafter as per manufacturer’s recommendation.The voltage accuracy shall be checked periodically to ensure absolute accuracy of the voltage settings.Also the battery shall be tested for proper voltage output as per manufacturer’s instructions.
Holiday Testing proceedure-The lining/coating sufficient drying or curing of the coating shall be ensured prior to conducting the holiday test of coating.Curing of the coating shall be completed as recommended by the coating manufacturer.
High voltage spark tester-High voltage spark testers are suitable for determining discontinuities in coating films of all thickness.It is recommended that the coating materials manufacturer shall be consulted before carrying out the test because certain type of coating can be damaged with high voltage spark tester.
The high voltage holiday testing shall be adjusted to proper voltage for the coating thickness being tested.In selecting the test voltage,sufficient test voltage shall be provided to break the air gap that exists at the holiday.This air gap varies depending on the total applied film thickness.The below given table may be used as a guideline for selecting the voltage to carry out spark of coating.
|Total dry film thickness (mills)||Recommended test voltage|
|8 ̴ 11||1,500|
|12 ̴ 15||2,000|
|16 ̴ 20||2,500|
|21 ̴ 40||3,000|
|41 ̴ 55||4,000|
|56 ̴ 80||6,000|
|81 ̴ 125||10,000|
|126 ̴ 185||15,000|
Prior to conducting holiday testing.The ground wire from the high voltage spark tester ground output terminal shall be attached to the conductive substrate,and positive electrical contact shall be ensured.Prior to starting the testing,coated surface shall be wiped and cleaned of all foreign particles,moisture etc.Holiday testing shall not be carried out using high voltage spark tester during rain or moisture weather.
The travel speed of the holiday exploring electrode shall be at a rate of approximately 0.3meter/second (1foot/sec.) using a single pass.
All hand held high voltage equipment shall be operated by authorized personnel only.When equipment is in on position the operator should not make body contact with the electrode.The operator should wear a rubber or plastic gloves and conductive boots while operating the equipment.The equipment shall not be operated in any combustible atmosphere.Damaged cables and plugs of the equipment shall be repaired or replaced immediately.
Procedure for repair of fiber glass internal lining.
Three repairs upto the metal of size less than 1 square inch per one square meter shall be spot repaired.Defective mats which exceed this criterion shall be stripped and relined.Pinholes and irregularities or holiday are found/detected,the defective area shall be completely removed,blasted to bare metal,primed and recoated with the same coating system as per client and manufacturer’s recommendation.Clicks the below mentioned link and see the details.https://jittuqaqc.com/surface-preparation-of-fiber-glass-lining-surface/
The repaired area and surrounding also shall be checked for holiday and thickness compliance.
When repair work is done under proper protection to the tank coating/lining shall be provided during blasting of damaged coating area.
Holiday testing of repaired lining area.
Sufficient drying or curing of repaired area coating shall be permitted prior to carrying out re-tested.Curing of the coating shall be completed as recommended by the coating manufacturer.
The repaired area testing also shall be carried out following the same procedure previously used with the same type of tester used.
All hand held high voltage equipment shall be operated by authorized personnel only.When equipment is in on position the operator should not make body contact with the electrode.
The operator should wear a rubber or plastic gloves and conductive boots while operating the equipment.The equipment shall not be operated in any combustible atmosphere.Damaged cables and plugs of the equipment shall be repaired or replaced immediately.