Anyone knows familiar with M suffix with API 5L X120M? 2

[salmon2]

Hi all,

This newest 44th edition of API 5L got some new pipe grades such as X100M or X120M.

The M means it is themomechanical rolled to 120ksi min yield. By the way, N means normalized and Q quenched&tempered.

So what is this themomechanical rolled process? According to 4.50 and 4.51 of API 5L, it is like a hot rolling followed by normalizing to me. Can it really get 120 yield without Q&T?

I am just curious about this new grade 5L and wonder if anyone can shed some light on me.

 

[SJones]

4.51 is the term applicable to X120 M. Since the plate rolling usually has an accelerated cooling by water spray at the end, it's not hot rolling plus normalising.

The attached 1995 paper from Europipe

http://www.europipe.de/pls/

http://www/wt_show.text_page?p_text_id=9769&p_lang=en&p_flag=(europipe)

shows that X100+ is not really a 'new grade' - it's just taken a while to formalise into a standard.

Steve Jones
Materials & Corrosion Engineer

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

 

[salmon2]

SJones,

Very good stuff, thanks a lot.

So it is ferritic-banitic microstructure achieved by hot rolling with accelerated cooling on plate. But I couldn't help wonder about integrity on the weld seam.

With the question mark on the weld, I really don't see any benefits compared with seamelss pipe which can be easily quenched and tempered to 100+ ksi. Of course, a little bit extra hardenability is needed for Q&T on seamless.

 

[metengr]

So what is this themomechanical rolled process?

There is lots of information on thermomechanical processing of steel plate. The plates are normally microalloy grades and are worked in the intercritical temperature region.

http://www.google.com/search?hl=en&q=thermomechanical+processing+of+steel+plate&btnG=Google+Search

 

[SJones]

seamless pipe which can be easily quenched and tempered to 100+ ksi

It can be achieved but, as you point out, only by pumping it full of alloying elements which have a serious impact on weldability.

Yes, there may be integrity worries over the weld seam as there could also be with the more established grades. It would be down to the purchaser's evaluation of the supplier's quality assurance and control for determining the necessary measures to ensure integrity.

If you can get a 30-inch, seamless X120 pipe from somebody - please let us know :-D

Steve Jones
Materials & Corrosion Engineer

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

 

[salmon2]

SJones,

I agree, for large OD, welded pipe will be more practical.

But still, the best weld seam will be normalized after welding. Therefore, I am still not convinced on the benefits of this special process over full body normalizing.

Salmon2

 

[SJones]

But if you normalised then you wouldn't get X120 properties! TMCP is not a special process - in fact, for most European and Japanese welded pipe mills, it's a long established, normal process.

Steve Jones
Materials & Corrosion Engineer

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

 

[salmon2]

I understand that if I normalized then I wouldn't get X120 on base. But my point is if anything overloaded, it will break at the weaker weld. The superior properties are not helping. The shortest board of a wood barrel determins how much water it can hold.

 

[SJones]

Why would the weld be weaker?

Steve Jones
Materials & Corrosion Engineer

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

 

[metengr]

If I may interject here, the weldability of TMCP steels has been studied over the years and these steels are known for both superior mechanical properties and weldability based tweaked carbon equivalents. I would not rush to any conclusion regarding TMCP welded pipe being weaker to N&T seam welded pipe without first reviewing current literature.

 

[salmon2]

I did review couple reports suggested by you guys, not all of them because I already understood TMCP will have or potentially if done correctly better properties than N or N&T.

But the best treatment you can do on weld of TMCP pipe is N or N&T, am I correct? So this welded TMCP pipe is as good as full body normalized on the weld seam. So I am curious how to justify the benefits of TMCP.

 

[SJones]

Well, one of the benefits has already been hammered out in this thread: achieving high strength without significant alloying. Another would be achieving an optimum microstructure without subsequent heat treatment thereby increasing productivity.

So this welded TMCP pipe is as good as full body normalized on the weld seam

What is the issue with the weld? It would be unusual (in Europe & Japan) to normalise SAWL (DSAW) pipe anyway - if you consult the old ISO 3183-3 you would note that Q&T was the only permitted post pipe forming heat treatment. The secret is to undertake sufficient research to select the optimum consumables and welding parameters such that 'good' welds are achieved without need for recourse to heat treatment. The principal 'bad' spot is more likely to be the HAZ and, as a purchaser, I would be looking for evidence from the manufacturer that they had 'cracked' any HAZ issues if you will excuse the pun.

Perhaps we are missing your point and it would be helpful to elaborate upon your specific concerns.

Steve Jones
Materials & Corrosion Engineer

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

 

[salmon2]

I do feel that I didn't make my point clear enough - maybe because of English being my 2nd language.

Per you say, I think I understand that TMCP has its benefits over traditional methods, such as high yield with low alloy (good weldability) and without heat treating afterward (high productivity). But to me the benefits only apply on the base material, not on the weld seam. For the weld seam, you still only got traditional methods which is why I boldly called weld is weaker.

For example, we use electric-welded 5L line pipes, tests have shown that the transverse Charpy @ weld is always lower than the one at base. The weld is the weaker point, right? With TMCP, it will further strengthen the base, but pretty much doing nothing on the weld (am I right on this statement?). So the weld seam remains as weak as before.