Sour Service Guided Bend Test

[mcsteel]

CSA Z245.1 specifies that ERW pipe must pass a root guided bend test in order to be qualified for sour service.

My question is: why is a root guided bend test necessary for sour service qualification?


Background: In the process of converting an existing Grade 359 Cat II pipeline for sour service, one of the cutouts met the microhardness requirements but snapped in half during the guided bend test...

 

[SJones]

One might assume that it is because CSA require proof of weld zone integrity that could lower the likelihood of SSC initiation. However, is it valid to apply the requirements for brand new pipe to pipe that has been in service? Did anyone look at ISO 15156-2, B.3 as a means of qualifying the existing material for H2S service?

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.

 

[mcsteel]

Steve,

Thank you for you comments, I agree that ISO 15156-2 B.3 may be a valuable test, especially if we encounter more failed bend tests.

The pipeline in question was previously in miscible hydrocarbon service and had no signs of degradation so I am still unsure as to what factors would cause the ERW to fail the bend test?

 

[SJones]

Was the pipe buried with cathodic protection?

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.

 

[mcsteel]

Steve,

Yes buried with extruded polyethylene coating and CP since about 1985.

Mike

 

[SJones]

There is a possibility that hydrogen generated by the CP could be playing a role in embrittlement during the test, but that theory gets a little difficult to follow if by "root bend" it is meant that the inside surface of the pipe is placed in tension (use of "root" in an ERW seam?). Ultimately, you will need to examine these failed tests in more detail to identify the fracture initiation point, ascertain the failure mode, and ascribe a degradation mechanism. It would be advisable to do this before embarking on an ISO 15156-2 test programme.

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.