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Cathodic Protection for Super Duplex Stainless Steel buried pipeline

Cathodic Protection for Super Duplex Stainless Steel buried pipeline

Cathodic Protection for Super Duplex Stainless Steel buried pipeline

(OP)
Hi,

We have installed 4 inch Super Duplex Stainless Steel (SDSS) pipeline around 2Km long and its service is Sour Gas. Our client suggested us to make a study whether Cathodic Protection (CP) system applicable or not? This pipeline was laid from Gas Compressor station to a Satellite station in a desert area (remote location). Please note,pipeline was coated with 3Layer Polyethylene/Polypropylene coating and thickness 0.010mA/m2.

My question is, why CP system required for this buried pipeline which material is SDSS, which is superior for all types of corrosion effects? (I have to prove to our Client that CP system is undesirable for SDSS pipeline)

RE: Cathodic Protection for Super Duplex Stainless Steel buried pipeline

Did the client specify CP as a requirement? What do the corrosion control standards that were to be applied demand? Several cathodic protection design standards incorporate duplex stainless steel requirements. Ultimately, someone has to be responsible for demonstrating that risk associated with failure of the pipeline is as low as reasonably practicable.

As to trying to assess the likelihood of corrosion damage occurring in order to assess the risk of a failure, you might wish to consult publications such as:

http://bookshop.europa.eu/en/corrosion-resistance-...

It is also worth noting that incorrectly applied CP can damage duplex stainless steel.

You would also have to ask why, if corrosion is not expected, does the pipe have a robust coating, even if the thickness has been quoted as an electrical current density (Freudian slip perhaps?).

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.

RE: Cathodic Protection for Super Duplex Stainless Steel buried pipeline

(OP)
Dear Jones,

Thanks for your information.

Basically the requirement for CP system was mentioned in FEED documents and even in engineering stage CP system was included in the scope. During installation our Quality person has requested Client for the approval of pad welding on pipeline and for that Client has responded by stating that "Cp system is not necessary for this pipeline as its material is SDSS". So our construction team has proceeded to complete the pipeline installation works. After a year our Client has requesting to install CP system for the pipeline, which will consume labor man hours, extra cost and time.

So we have to show to Client that, CP system was actually suggested for over protection which is not necessary for this SDSS pipeline.

Please guide me if we didn't install CP system then what other measures we have to take to ensure the safety of the pipeline?

RE: Cathodic Protection for Super Duplex Stainless Steel buried pipeline

I have every sympathy for you given the comedy of errors. Sounds like the average Middle East pipeline job. Good luck.

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.

RE: Cathodic Protection for Super Duplex Stainless Steel buried pipeline

Is the entire pipeline route always dry? Like forever?
If not then you need to pay attention to CP.
The customer may not always be correct, but they are 'right'.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Cathodic Protection for Super Duplex Stainless Steel buried pipeline

CP system was indicated in FEED docs and it was also included in the scope of work. Is there any excuse for not installing it then during project execution?

RE: Cathodic Protection for Super Duplex Stainless Steel buried pipeline

Yes, because the client said it wasn't needed. Hopefully, that statement was recorded in an official communication.

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.

RE: Cathodic Protection for Super Duplex Stainless Steel buried pipeline

It will depend on temperature and moisture and chloride content. What is the temp immediately after compression or do you cool the gas after compression? Is the line near a sea? Can it be located in a seasonal water table?

Finally if the owner has specified, in writing, that CP is not required, simply comply. You may comply with a caveat as well indicating your evaluation as to the need for CP.

Many years ago the gas utility that I worked for installed 316 as risers to the gas meters without CP. Crevice corosion due to chlorides being concentrated due to lawn watering an evaporation caused perforations in the a number of risers within a few years.

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