CP and duplex stainless steel 2

[Farzin1342]

As we all know application of CP on duplex stainless steels may make them vulnerable to hydroegn embrittlement, the mechansims being that the hydrogen atoms formed as a result of CP, will be joined together while inside the crystal structure of the steel, thus producing hydrogen gas that within those very tiny vacancies can produce very high pressures, resulting in failure.I wonder if by the advances in materials science any solution has come up yet to overcome this problem.

Thank you in advance.

 

[pradipgoswami]

HiFarzin 1342,

Industry experinces indicate Duplex S.S are prone to HISC under cathodic protection.

Duplex stainless steels are regarded as potentially susceptible to HISC,independent of SMYS(typically 400 to 550 MPa)or specified maximum hardness.Welding may cause increased HISC susceptibility in the weld metal and in the HAZ adjacent to the fusion line.This is related to an increased ferrite content rather than hardness.
Qualification of welding should therefore prove that the maximum ferrite content in the weld metal and the inner HAZ
about 0.1 mm wide) can be efficiently controlled; contents of maximum 60 to 70% are typically specified.

Design precautions should include 1) measures to avoid local plastic yielding and 2) use of coating systems qualified for e.g.resistance to disbondment by mechanical and physical/chemical effects.

Good design principles are very essential requirement for design of cahtodic system,more so since working environments of Duplex S.S always are demanding.

The attached documents provides a good design background on cathodic protection of duplex S.S.

Thanks

Pradip Goswami.

 

[SJones]

hydrogen atoms formed as a result of CP, will be joined together while inside the crystal structure of the steel, thus producing hydrogen gas that within those very tiny vacancies can produce very high pressures, resulting in failure

This is the explanation for HIC of carbon steel in H2S containing service. NACE Corrosion 2005, Paper 05098 gives an overview of hydrogen embrittlement of duplex stainless steels. Unfortunately, the adopted terminology for the phenomenon now appears to be HISC.

The document that appears not to have been attached in the above posting, may have been:

https://exchange.dnv.com/Publishing/Codes/download.asp?url=2008-10/rp-f112.pdf

Steve Jones
Materials & Corrosion Engineer

http://www.oilandgaspeople.com/cv/11499664

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