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minimum carbon in API 5L pipe steel

minimum carbon in API 5L pipe steel

minimum carbon in API 5L pipe steel

(OP)
A pipe mill is proposing a minimum level of 0.04% carbon for API 5L X65 steel.  This is for subsea pipe that will be operating around (+) 40 deg. F, subjected to near 0.25% strain levels during installation.  Anyone have an opinion on if this is too low?  The client specification stated a minimum of 0.07%.

RE: minimum carbon in API 5L pipe steel

I expect that you will have problems with meeting the tensile requirements in welding procedure qualification with such low carbon content - without further steel chemistry info.

RE: minimum carbon in API 5L pipe steel

Issue is low strength long seam HAZ of what I assume is TMCP plate long seam welded into pipe.  Laying strains will concentrate in tbe low strength region and could fail/collapse there first.  

The mill wants to shoot for 0.05 to 0.06C.  The 0.07min means actual would be 0.08-0.09 which is quite high for TMCP.  The client thinks they can avoid the problem by specing 0.07min.  And for an offshore laying job, it is a real concern.  

If you have suppliers that meet all requirements, honor the clients requirements.  If not or if big $$ difference, ask the pipe mill why they want the lower carbon and then see if the client will go for it.

RE: minimum carbon in API 5L pipe steel

Agree with grampi1 as well.  I would ask the pipe manufacturer to provide weld qualification records to verify tensile properties after welding.  Too low Yield strength in the girth seam HAZ could lead to a major fishing expedition!

RE: minimum carbon in API 5L pipe steel

(OP)
The pipe is seamless any may possibly be reeled.  As I can tell, there is no good reason the client had specified a minimum carbon level of 0.07%.  Thanks for the info on the girth weld HAZ, that may lead to an interesting discussion.

RE: minimum carbon in API 5L pipe steel

Note 0.07C is actually quite low for a seamless.  Am guessing this is for an X60-X70 grade, which usually means Q&T for seamless.  Even 0.07 will have trouble making the enhanced strength.  If 0.07C or less and strength from Q&T, watch out for high microalloy additions (V and Nb).

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