Testing Above Grade Isolating Flange

[salimkas]

We have in our company about 3 KM length pipeline with cathodic protection. The line take about 3 A Current. The contactor gave the reason for this high current is draining of the current from isolation flange. We tried ON/OFF survey and the results of it shown the difference of 10 mV between the ON and OFF in station side (after isolation flange), , is this indication evidence of failure in the flange ? any one has NACE standard for this point

Thanks in advance

 

[LittleInch]

Is this line new or existing?. If new then make him replace the flange.

If not have you tried measuring the resistance across the flange? A well coated pipeline should have a significant resistance.

The fact that there is any change in potential on the station side (where was this referenced from ?) gives rise to some concern, but could be due to other reasons.

Isolating flanges are notorious for failure either of the gasket or the insulating washers and sleeves for the bolts. Can you post a photo or give some details, size, flange rating etc.

Also check if there is any other contact between the pipeline and any support or metallic item connected to ground before the flange.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[brimmer]

You can easily check with an insulation checker to determine if shorted or not. You may also be able to try a signal trace method to see if any current makes it past the flange. The fact that you do get a shift in the station piping from on to off is telling you that there is some current getting into the station piping from the rectifier(s) you interrupted. It may be getting there from a different path than the flange with the kit though, but you can start with measurements at the flange. More tests needed to get a difinitive answer of laction of short.

Don't know what size/age/conditions there are at your line. Sandy/rocky soil, poor coating, larger diameter pipeline will require more current. If the line is new I would say this is too much current.

 

[SJones]

NACE SP0286 (and no, I cannot email you a soft copy)

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.