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Minimum Carbon content for API 5L X60
3

Minimum Carbon content for API 5L X60

Minimum Carbon content for API 5L X60

(OP)
Dear all,

Anyone know about the minimum carbon Wt% for API 5L X60. According to the specification the maximum carbon content 0.28 wt%. My PMI results shows the carbon content of 0.05 wt%. However the microstructure is tempered martensite with the hardness of 210HV, Yield strength of 520 MPa, UTS=564 MPa and elongation is 31.5%. Mn content is 1.33 wt.%. Is the carbon content sufficient to form martensite? Is the carbon content represent hardness and UTS value?

Any comment is highly appreciated.

Thank you

RE: Minimum Carbon content for API 5L X60

I always thought PMI didn't show carbon content. Apparently it does? If so, what is the accuracy?

RE: Minimum Carbon content for API 5L X60

Are you sure of the carbon content? Most PMI equipment (XRF) cannot accurately measure C.

RE: Minimum Carbon content for API 5L X60

(OP)
I always thought PMI didn't show carbon content. Apparently it does? If so, what is the accuracy?
Kingnero ..Laser Induced Breakdown Spectroscopy (LIBS) by Brunker claims that it can detect carbon but I am also worried about the accuracy. LIBS using laser instead of XRF. I will reconfirm using spark spectroscopy.

Are you sure of the carbon content? Most PMI equipment (XRF) cannot accurately measure C.
Weldstan..Agree with you and I will confirm by spark spectroscopy. Will update the results when available.

Thank you for the comments.

RE: Minimum Carbon content for API 5L X60

In 1993 and 1994 when I worked in the UK, we had a contractor with an portable optical spectrograph who could accurately detect C under an Argon shield and we compared it with a number of LECO tests on same samples. We performed 100% PMI on materials and welds.

RE: Minimum Carbon content for API 5L X60

(OP)
In 1993 and 1994 when I worked in the UK, we had a contractor with an portable optical spectrograph who could accurately detect C under an Argon shield and we compared it with a number of LECO tests on same samples. We performed 100% PMI on materials and welds.
Weldstan...LIBS used laser to spark under argon environment and analyse using spectroscopy. I did not analyse using LIBS but I used XRF. I doubt about the value for carbon as it is too low to get the measured mechanical properties and microstructure.

RE: Minimum Carbon content for API 5L X60

I expect you have the traditional micro alloy / control rolled pipe material . The carbon should be very low. The key is Nb ( used to be Cb in the US), maybe Ti . I assume it is ERW pipe , skelp is rolled and coiled at a specific temperature . The steel age hardens in the hot coil. Not dependent on martensite. The great advantage is you can have very low carbon for excellent weldability of the ERW weld and the field welds. The critical point is recrystallation of the ERW weld . The induction reheat must cover the whole ERW . The mill people on API 5 kept trying to get loop holes in the 5L ( the latest 5L I have is about 1995 , as obsolete as me ). If the steel is not very clean ,outbent fibers at the ERW could be a problem . Great steel with a little QC. This material is also used extensively for API 5 CT casing. Mill certs should say something about metallographic exam of the ERW at some frequency.

RE: Minimum Carbon content for API 5L X60

(OP)
Blacksmith...This is not the ERW pipe but seamless production riser used to transport methane offshore from the platform to another platform. The riser is seamless made of API 5L X60. According to the specification, the pipe can be supplied as rolled, normalised rolled, thermomechanical rolled, thermomechanical formed normalizing formed, normalizing and tempered and quenched and tempered. Since we do not have the manufacturing data about this pipe, we did metallography and found out that the microstructure is tempered martensite and the hardness of 210HV, Yield strength of 520 MPa, UTS=564 MPa and elongation is 31.5%. So we concluded that the pipe is seamless (no indication of weldment in the microstructure) and supplied in the form of quenched and tempered as the microstructure is tempered martensite. The mechanical properties meets the requirement for API 5L X60. However when we did the PMI we found that the carbon content for the pipe is 0.05Wt% . With low carbon content and Mn of 1.33% I just wondering how martensite can be formed. I doubt the PMI result and will try to analyse the pipe using spark spectroscopy tomorrow. If the maximum carbon content for API %L X60 is 0.28Wt% without stating the minimum, is 0.05% acceptable?

RE: Minimum Carbon content for API 5L X60

I am not familiar with an XRF that can detect carbon. The when we bought a Niton several years ago we looked at all of the competitors and none would provide carbon. Even the OES and LIBS that can give you carbon are very dependent on your surface prep. Just testing the surface can give you a false reading depending on how it was processed. Your best bet is to send a sample to a lab for analysis. It is pretty trivial for someone with a spectrometer and LECO to tell you what you have.

RE: Minimum Carbon content for API 5L X60

C is measured by OE, combustion, or LIBS, it cannot be measured by XRF.
This may well be TMF seamless.
My guess is that you misinterpreting the micros. Yes, there are multiple phases but they are not traditional martensite.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Minimum Carbon content for API 5L X60

(OP)
Does anybody know why we do not see any comment from mtengr lately?

RE: Minimum Carbon content for API 5L X60

For what it is worth ; the 1995 5 L( 41 st Ed.) lists no minimum carbon for any grade. Did you get a Nb /Cb , or V or Ti ?

RE: Minimum Carbon content for API 5L X60

(OP)
For what it is worth ; the 1995 5 L( 41 st Ed.) lists no minimum carbon for any grade. Did you get a Nb /Cb , or V or Ti ?
blacksmith37...Thank you for your comment...Nb=0.008, Ti=0.011, V=0.021
Nb+V+Ti=0.0409<0.15.
I am sorry, I am familiar with microalloyed steel. Can anybody comment on the microstructure?. What microstructure is it and in what condition the material was supplied. It looks like martensite/bainite with ferrite and carbides or could it be acicular ferrite with carbides.. We lost the mill certificate as it was manufactured in late 80s.
There is a mistake in my statement. We are not using XRF far the analysis. I have to check it out.

Based on the carbon content, if the result is true, is 0.05% acceptable for API 5L X60?

Another issue is that, should the material is ERW can we see the microstructure of the weldment by macro etching?

RE: Minimum Carbon content for API 5L X60

Yes - the result is acceptable and is typical of current Japanese pipe mill chemistry. And, yes, you should pick out a weld seam by macroetching as the seam should have received a local inline heat treatment that will affect the etching response.

Steve Jones
Corrosion Management Consultant

www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

RE: Minimum Carbon content for API 5L X60

(OP)
Sjones ...Thank you very much for the the info...Actually we used spark spectroscopy for the analysis and not XRF..I made a mistake. We try to confirm carbon content and it shows almost similar value 0.048% carbon.
So I conclude as follows:
1. The composition meet the specification for API 5L X60.
2. Seamless
3. Complex microstructure with martensite/bainite and acicular ferrite.
4. Supplied in the TMF condition.

Thank you very much for the comments. I really appreciated them.


RE: Minimum Carbon content for API 5L X60

Quote (replica)

3. Complex microstructure with martensite/bainite and acicular ferrite.

That seems exceedingly complex for X60. Is the metallurgist performing the assessment familiar with this type of steel?

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Minimum Carbon content for API 5L X60

@ironic

Take a look at the quoted yield strength - it's heading towards higher grade territory

Steve Jones
Corrosion Management Consultant

www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

RE: Minimum Carbon content for API 5L X60

(OP)
If we want to change the riser ..what material is suitable for the offshore application? The operation exposed to cyclic loading, tensile, torsion and bending. The methane contains CO2 and also traces of H2S even though the area is 'sweet crude'. Is upgrading to API 5L PSL2 X60N will be better than API 5L PSL1 X60. The riser parted at the splash zone due to corrosion fatigue ..hydrogen blistering induced fatigue. We found many hydrogen blisters at the internal surface of the riser. Does internal cladding at splash zone with stainless steel will be a good idea for the application?

Comments are highly appreciated.

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