Methods of testing the integrity of isolation joints and flanges.
- High resistance voltmeter.
- Megga style ground resistance meter.
- 12 volt battery.
- Sensitive magnetic directional compass.
18.1. The isolation joint or insulated flange should be supported in electrical isolation from the ground. This can be achieved by supporting it on dry wood and a neoprene pad.
18.1.1. Connect an electrical resistance meter from one side of the isolation joint to the other. The meter should show the maximum resistance. If it does not, then the whole joint should be cleaned and dried, both inside and out.
NOTE. A thin film of moisture, or a small amount of dirt can conduct enough current to cause an error in the meter reading.
126.96.36.199. Connect one pole of a 12 volt battery to an earthing pin and the other pole to one side of the isolation joint.
188.8.131.52. Place the copper/copper-sulphate electrode in the ground remote from the 12 volt earthing pin.
184.108.40.206. Connect a high resistance voltmeter between the electrode and the side of the isolation joint which is connected to the battery.
220.127.116.11. Note the voltage reading.
18.104.22.168. Connect the high resistance voltmeter between the electrode and the side of the isolation joint which is NOT connected to the battery.
NOTE. There should be no reading obtainable on this side of the isolation joint as the insulation should be greater than that of the meter. If there is a reading then the condition should be checked to make sure that there is no contact with the ground. This contact can be through the human body or a tuft of grass etc. so great care must be taken.
Do not attempt to test the joint by 'shorting' the battery to see if a spark occurs. This has been practiced in the past but can result in permanent damage to a joint which merely needed cleaning or drying.
18.2. Clean the joint and make sure that there is no direct metallic connection from one side to the other.
NOTE. It might be necessary to make continuity tests on instrument fittings and electrical earthing points which are common within manifold areas.
18.2.1. Ensure that the cathodic protection system is on.
18.2.2. Connect a high resistance voltmeter from one side of the isolation joint to the other and note the voltage.
18.2.3. Switch the cathodic protection system off and note the voltage again.
NOTE. The voltage should change substantially and might even reverse polarity if the insulation of the joint is good.
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