temporary cathodic protection

[loukasse]

Dear expert,
Our Contractor have to Install temporary cathodic protection in buried pipeline
Length 12 km
Diameter 14 INCH
COATIONF 3 LPE
He purpose to install only 3 anode MG weight 15 kg.
My opinion is insufficient 3 anodes for 12 km.
Please advise

 

[SJones]

Ask to see the calculations made by the ISO 15257 Level 4 certificated CP specialist for on land metallic structures employed by the Contractor. Ensure that the calculations include a copy of the certification.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

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

 

[alain0707]

I think is not sufficient if you consider intensity values of anode.
This pipeline must to be protected fully lenght.

 

[LittleInch]

Your opinion is the same as mine.

The spacing of sacrificial anodes inshore is about 500m maybe, but very dependant on soil conditions.

Ask for the calcs like Steve says and see what happens.

As these are only for a short period you don't need many kg, but you need a lot closer spacing.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dik]

What is the normal spacing for 'normal' environments; I'd thought that the spacing was in the order of 200m. I suspect it can vary a lot.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[SJones]

Gents don't mix up your experiences of anode spacing with offshore sacrificial anodes for a 30 year design life. With a quality 3LPE coating, it's surprising how much pipe length can be protected from a sacrificial anode groundbed. Nevertheless, get the calcs, and the qualification of the person making them.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

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

 

[dik]

@Steve: Do you have a copy of the calculations for this? I'd just like to know what really goes into this. By sacrificial ground bed, are you referring to a granular bed with conductors and sacrificial anodes embedded in it? It's a learning process.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[TugboatEng]

SJones, out of curiosity, how does soil conductivity affect anode spacing? Do more conductive soils allow greater spacing?

 

[SJones]

Gents - your interest in CP is admirable. Unfortunately, I can only give you outline answers.

The governing standard for the subject of the thread is ISO 15589-1, and the calcs to run through are highlighted there. Unfortunately, I don't have any samples (produced by specialists, which in no way I am). As the ISO document says, sacrificial anodes work best when current demand is low, as is the case with a high quality, as-installed pipe coating with any damage located and repaired); and, in low resistivity environments: swamps, marshes, high water table areas. However, those statements are geared towards whole of life protection of the pipeline, and not just a relatively brief period prior to commissioning of the impressed current system (that I hope the OP will be deploying). The anodes are not just stuck in the ground as is. They are usually supplied in bags containing a mixture of materials to provide a low resistivity, moisture retaining environment in proximity to the anode:

http://www.bacgroup.com/Global/BAC/CP Catalogue/1.1.4 SuperMAG Anodes.pdf

. Three anodes does seem a bit light as it usually takes two or three anodes at each drain point location to get the necessary geometry for the electrical characteristics. There should then be an attenutation calculation to work out the separation of anodes along the line. All of this needs to be documented and presented.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

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

 

[dik]

Thanks, Steve...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[LittleInch]

Steve,

Trust me I'm not mixing it up.

Everything I've even seen for onshore pipelines with sacrificial anodes says that in "normal" soils, the throw of an individual anode is between 150 to 200m. Hence a spacing of around 300 to 400m between each one. Which is why you don't see it done very often for any pipeline more than a few km long or to boost the protection in small areas.

Now for temporary protection you don't need the mass of an anode to be very high to supply voltage for very long, especially for new pipelines so indeed the temporary effect might be better, but I wouldn't like to see much more than 500m spacing. Sacrificial anodes only have small driving voltages compared to impressed current.

So the point remains that 3 anode bags of 5kg each (we don't even know if these are in one place or every 3km) is woefully inadequate to actually protect a 12" onshore pipeline 12km long.

CP remains thought the blackest of black arts when it comes to pipeline design....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dik]

That's why I'd like to get added info on this black arts juju...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[SJones]

It's only a 'black art' when it's performed by unqualified people, and reported poorly. My interpretation of the OP was 3 x 15kg anodes, i.e. 45 kg

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

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

 

[dik]

@Steve: Thanks for the caution.

I like to have a good understanding of things, even technical stuff (I'm a bit of an info junkie, and I haven't lost my childhood curiosity)... and there still can be some 'magic' in how they work. Don't worry, I'm not going to jump into designing cathodic protection systems just because I have a better understanding of them.

With this particular thread, 3 anodes in 12 km would have run up a flag since spacing that I've encountered is approx 200m and I would have had someone look into it or at least raised the question... had it been 500m, I may or may not have asked the question... but 4000m is a lot greater than anything I've ever encountered. The disturbing issue was the distance and not the mass.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[SJones]

@dik - you're not alone. I'm sure many on here share your desire to carry on learning. I certainly do.

What I'm trying to get across is that we shouldn't bandy figures about when we have the minimal amount of information. The quoted standard has the methodology and formulae to work through. All the competent (certified) person then has to do is plug in the variables, and produce a quality report.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

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

 

[dik]

thanks, Steve

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[EdStainless]

It was explained to me once that CP in water is limited by the anodes, you know the water properties.
In soil the limit is the soil, the results that you get will be limited by how accurately you characterize the soil conditions. And being aware that the soil properties will change seasonally in most places.
I can't imagine getting enough throw to cover that length with 3 anodes. The 15kg may be right, but as 30 x 500g or something like that.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[dik]

more info... thanks. Can a geotekkie drop in?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik