CATHODIC PROTECTION OF DUPLEX STAINLESS STEEL 3

[FYS]

Dear All,

What is the upper/lower limit cathodic protection criteria for coated buried DUPLEX STAINLESS STEEL pipeline in soil.

Thanks
Best Regards

 

[TVP]

Have you reviewed ISO 15589-2? The limits are essentially -500 to -800 mV. DNV-RP-F103 and NORSOK M-503 are good resources that are freely available to download over the internet in case you have not purchased ISO 15589-2.


DNV-RP-F103 CATHODIC PROTECTION OF SUBMARINE PIPELINES BY GALVANIC ANODES

http://exchange.dnv.com/OGPI/OffshorePubs/Members/rp-f103.pdf

NORSOK M-503 Cathodic protection

http://www.standard.no/PageFiles/1198/NORSOK_M-503_utgave_3.pdf

 

[strider6]

have a look also at:
DESIGN OF DUPLEX STAINLESS
STEEL SUBSEA EQUIPMENT
EXPOSED TO
CATHODIC PROTECTION

http://www.dnv.com/binaries/RP_F112_tcm4-184069.pdf

S

Corrosion Control

 

[SJones]

Why are you all quoting offshore design specifications when the question relates to onshore buried pipe?

Steve Jones
Materials & Corrosion Engineer

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

 

[TVP]

Wow, I am not sure how I missed that. My apologies for the oversight, and thanks to Steve for noticing the error. ISO 15589-1 is the appropriate standard for on-land (buried) pipelines. The following is an excerpt from section 5.3.2 Protection criteria:

Stainless steels and other corrosion-resistant alloys generally need protection potentials more positive than ?850 mV referred to CSE; however, for most practical applications this value can be used.

This limit is similar to that for offshore applications due to the detrimental effects in the material caused by hydrogen formation at the metal surface when using CP. An upper limit of ?500 mV could likewise be implemented, although it is not specifically stated in the standard.

 

[SJones]

It's OK. Most CP questions relate to offshore, so it's easy to go into auto mode. Having said that, the hydrogen embrittlement issue is still a valid one and this degradation mode will have to be considered in establishing a lower negative potential limit. EN 12954 quotes an upper (positive) limit of -0.45V CSE but also advises that the protection potential should be established by testing. CP of duplex is just that bit trickier compared to austenitics because of hydrogen embrittlement.

Steve Jones
Materials & Corrosion Engineer

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

 

[EdStainless]

You have to treat duplex grades like ferritic alloys (since they are 50% ferrite). They will hydrogen embrittle if you get too carried away.

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