Conductivity on a buried pipeline

[awol]

We have applied an insulator to a buried pipeline and are in the process of validating the effectiveness of the insulator. The insulator isolates a bolt-on sleeve from the pipline. One engineer used an ohm meter and measures resistance. Any resistance reading is considered a failed validation test. Another engineer uses the connectivity setting on the ohm meter and hears a beep if a connection is located. The latter engineer is using the setting normally used to check if a wire has a short.

Which method is accurate? Which method provided the true answer if a component is checked for contact to the steel pipe? Is there a threshold ohm value that defines connectivity or is any resistance measured a bad thing?
Thanks, AWOL

 

[rconner]

Not claiming expertise here but while perhaps not intentionally, it appears you have indicated that the line may have been "buried" when this conductivity check was somehow conducted. You may want to provide perhaps more/better information, to get a response that might help you. e.g. maybe at least a brief dscription of the piping/surroundings involved, exactly where were the probes or clamps etc. placed, and also what was the exact resistance measured by one "engineer"/the ohmmeter? Wasalso curious if the piping was empty or full (of a fluid/water etc.?) and was any of it between the connections actually already backfilled when checked? Also, what exactly is the specific design function of this "insulator" you are talking about (this could help experts with your last question)?

 

[IRstuff]

The simple question is "What is the requirement?"

Do you need 200 ohms isolation or 2 megohms isolation?

Once you know the requirement, the correct test method will be obvious.

TTFN

FAQ731-376

 

[brimmer]

A quick check is to use the ohm setting on multimeter to see if the circuit is open or closed. If it is not open, you might have a short somewhere or current transfer in a different manner. I suspect there is some transfer of electric current in this case from your description. Testing the insulation kits can also be completed by potential difference method. There is specialized equipment to test the kits, if partial or complete continuity is noted or suspected you can test with a “Swain” meter to measure current transfer, quantity and direction of current. An insulation checker such as a “Gas Electronics Model 601 Insulation Checker” can be also be used, can even tell magnitude of short at each bolt. The “Insulation Checker” works by applying a radio frequency across the insulating kit to determine any transfer.

 

[awol]

As always, great responses from all.
*Our final application will be on buried liquid and gas pipeline under pressure. Our test is on empty pipes in a lab (not buried). Our goal is to provide a steel repair clamp that is isolated from the pipe as not to affect any induced current or other corrosion protection systems that the pipeline already has in place. The purpose of our insulating material is to isolate the clamp from the pipe and avoid a location of corrosion.
*Knowing the requirements is one of our biggest issues. Company xyz that supplies Flange Isolation Kits to pipeline operators use a 500 ohm plus guideline. If the flange-to-pipe measures greater than 500 ohms, is is considered to be isolated. We cannot use this value for our application but I am looking for guidance, such as a NACE standard.
*The RF isolation meters are great tools for this project as suggested. I will look into a service to have this done. Again, if I cannot validate a go/ no go answer, I will be back to measuring an ohm value and have to determine if it is high enough per industry standards.

Here is some information a NACE engineer in CA shared. Set up the Wavetek (we have the 85XT) to measure ohms. Even if it reads ohm values, the meter must stabilize to a value. If the ohm value jumps around and does not stabilize, there is no connectivity. Period. In trying this, I cannot get a stable reading; it jumps around.
I plan to pursue the model 601 to get thrid-party opinion.

Any more ideas? Thanks for the great responses.-awol

 

[rconner]

You have now certainly at least some better explained what you are actually doing, but I am still a little confused as to the intent. This is probably a stupid question, but I was just curious how corrosion protection is to be supplied to your "steel repair clamp"? (I guess I'm just trying to understand why it would not be adviseable e.g. to reasonably bond the clamp to the pipeline e.g. with field jumpers, instead of insulated from, and then it would seem the clamp could perhaps be cathodically protected along with the line/as I suspect most oil and gas pipelines now are?)

 

[dcasto]

I'm with rconner. You have isolated the clamp and now it will corrode instantaneously (so to speak). I would also guess that the unbonded piece of steel will rob the pipe of protection, just like an interference from another pipeline.

I'd hope you would at least coat and wrap the device and put a small mag anode on it, if it is indeed isolated from the pipeline.

 

[awol]

There is a concern about placing a conductive (steel) part on a cathodically protected pipeline. Something about disrupting a balance and causing accelerated corrosion. Our clamp is wrapped and coated well and I don't anticipate a stand-alone corrosion issue with it. The pipeline owners are acceptable to the addition of the clamp IF we can validate that it is in fact "isolated" from the pipeline. Hence the reason for an isolation barrier and a method to validate the isolation. Again, cathotic protection and isolation is not my strong point. We provide bolt-on items for pipelines. We may need an anode as suggested after isolation is achieved. Thanks again.

 

[rconner]

I would certainly not question the general utility of a suitably designed repair clamp, nor would I necessarily want to "disrupt a balance" (whatever that means!) Also, I would not downplay the encouragement, "The pipeline owners are acceptable to the addition of the clamp IF we can validate that it is in fact "isolated" from the pipeline."
However, you might also want to check the requirements of regulators/laws etc. in the application/locales you are dealing with (even though you " don't anticipate a stand-alone corrosion issue with it).

 

[brimmer]

Thanks for the additional info, this changes things a bit, I thought you were just installing an insulating gasket where the pipe comes above ground. This brings up an interesting dilemma, to isolate the clamp or not. Generally the idea here is when you attach a new piece of steel to an older piece, that new section will be anodic to the old piece, and you can have accelerated corrosion (large cathode/small anode scenario), so the concept is isolate the new piece (same is true for old pipe/new piece of pipe scenario). The problem is when you isolate the new piece, which you will coat, it will not be protected and any holiday/coating defect over time will be anodic producing the same scenario, large cathode/small anode where localized corrosion will occur at a fast rate. If you do isolate the clamp, I would suggest you install an anode to protect it. The other scenario is to not isolate the clamp, coat it, and allow the existing cathodic protection to protect this piece as well. If the clamp is the same material as the pipe, well coated with no defects, CP system is working well and you complete tests this should work as well. You could again install an anode attached to the clamp if you don't think there is sufficient protection, some current will leak out on the pipeline of course but the entire area will be augmented by the anode.

 

[brimmer]

Forgot to mention, if you do isolate the clamp you might have to put a bond connecting the pipeline sections upstream and downstream of the clamp depending on the current CP system (not sure if there is only 1 recitfier or more and where they are located in relation to the clamp). I think the best alternative is to forego the isolation, just make sure the clamp is electrically connected to the pipeline (you might have to bond the clamp to the carrier pipe depending on how the clamp is attached) and it will be protected as well. CP system shouldn't loose current here as it is newley coated. Many pipeline operators only use clamps as a temporary repair method, they are not accepted as a permanent repair, but this is a different issue...