API 5L X65MS Microstructure

[goodbadgood]

Hi

I have 1 metallurgical sample of API 5L grade X65MS pipe.
I have done micro structure analysis and found microstructure to be granular bainite.
Let me know with your experience if my interpretation is right.
Also there is an HIC crack and in that crack i found inclusions marked by red circle. Does it look like an inclusion?

 

[metengr]

The microstructure looks more like an acicular ferrite matrix containing small colonies of carbides. The crack is transgranular but I see no red circles indicating inclusions.

 

[goodbadgood]

metengr

Sorry to missed the red circles. Actually the micro graph is not giving correct contrast but i see clear differentiation in contrast under the microscope. These inclusions are located at few locations inside the crack. literature states that the presence of inclusions makes the material susceptable to HIC. I will send this sample for EDS analysis.

 

[metengr]

goodbadgood;
Yes, I would agree that is an inclusion you identified. I take it the pipe was supplied in the normalized HT condition.

 

[pradipgoswami]

goodbadgood,

Effect of sulfide inclusion, MnS in particular is well documented for generation and propagation of HIC cracking in sour media.Pipeline steels resistant to such damages are often Calcium treated so as to control the extent of MnS formation and avoid excessive formation of MnS stringers on rolling.

The photo shown above have multiple stringers along the length of the crack. It's important to know how high was the PH2S,and the pH level of the operating media, which are one of the major contributing factors of HIC. The micro structure shown above is generally uniform in all other places, except it shows some banded micro-structure , both on top and bottom half of the crack. This may be be some in-homogeneity during rolling of the plates. Banded structures are more prone to HIC attack than the uniform ones.
Going back to the basic:- the manufacturing history of the steel would be important. Also if this pipe is a seamless or welded pipe.If the later chances of HIC would be more, due to high residual stress and hardness.

You may refer the attached article to get additional information.

Thanks.




Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Ontario,Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299
All provided answer are personal opinions or personal judgements only. It's not connected with any employers by any means.

 

[SJones]

Since this is TMCP material it is more likely to be a seam welded pipe. It is assumed that it has been subjected to a standard NACE TM0284 HIC test with 1 bar H2S. It would be interesting to know the following:

a) magnifications of the micrographs
b) thickness
c) the location of the cracking within the pipe wall
d) which TM0284 cracking parameter(s) has the material 'failed' to comply with and what are the acceptance criteria




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.

 

[goodbadgood]

@Pradipgoswami

Thanks for your reply. Yes stringers were observed throughout the length of the crack.
The HIC test was carried out as per the requirements of NACE TM0284.
Pipe is seam weld pipe and the sample was extracted near the weld.
a) Pressure: H2S concentration, saturated condition = 2,600 ppm to 3,200 ppm
b) Environment: pH = 2.9 to 3.3


@Sjones
a) Micrograph was taken at 500X magnification due to low quality camera, photographs are not as good as it looks with naked eye in the eyepiece of the microscope.
b) Thickness is 10mm
c) At midthickness cracks were observed after the test
d) Average CTR ≤ 3%, CLR ≤ 10%, CSR ≤ 2%.
e) Crack length is 6mm

 

[SJones]

See if the microstructure in the immediate vicinity of the crack can be ascribed to low temperature transformation products.

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.

 

[goodbadgood]

The max. Sulfur content allowed in the specification is 0.002% but it was found that S content is actually 0.004%. This could explain the presence of inclusions (MnS)

 

[weldstan]

Inclusion shape control may also have been omitted.

 

[SJones]

All good points, but if the material has only cracked in one specific location it suggests something more than sulphur content and shape control issues.

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.

 

[goodbadgood]

Sjones

Is it something to do with plate bending process or expansion process what do you think about it?

 

[metengr]

I believe it would have more to do with segregation of alloying elements in the TMCP material. I have seen this happen with PV plate steels affected by the Mn content.