Why are thermo-mechanically formed steels so popular for piping? 1

[kingnero]

For piping of many products in the oil and gas industry, standard API 5L and ISO 3183 pipes are of the TM variety.
The commercial advantage is that a lower C% (and according C-equivalent) of TM steels is favorable for welding.
However, during welding, the zone surrounding the weld is no longer of the high, TM quality but is locally transformed, quite possibly coarse-grained steel with lower mechanical properties as the not-affected base material, introducing a weak spot at every weld zone.

Why do most suppliers (only) offer TM, instead of normalized or as-rolled steel?
When asked to suppliers, they hide after "that's the way we've always done it", without offering a valid, technical reason.

Reasons I do not believe are valid are:
- TM is cheaper to produce (probably on the contrary)
- AR or N has lower mechanical properties (you'll need a suitable chemistry, but you'll get into TM territory without problems)
- AR or N needs is more difficult to weld (partially correct, but can easily be solved with a procedure requiring 50F higher preheat, if that much is required)

I appreciate your input!

 

[kingnero]

Small bump:
Does nobody answer this question because I'm asking things that don't occur or play no part in the States (I presume most of the members are from the USA) ? Perhaps you're using other steel qualities for pipelines ?

Anybody cares to share his/her opinion, even if it is only slightly related to this question?

Many thanks in advance!

 

[LittleInch]

Maybe because we don't know either.

The materials engineers might have a view.

For me as long as it complies with 5L / 3183 I don't really care how they make it.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[IRstuff]

Question more suitable for forum330?

To avoid double posting, perhaps post a link to this thread

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[weldstan]

TM pipeline steels were developed by Japanese mills in the 1970s and a number of countries' mills eventually followed suit to provide low toughness proerties desired by ever more customers. With regard to circ seam welds weld procedure qualification on these TM tubulars proved that the HAZ met toughness requirements. It is more than likely that once mills had introduced the equipment necessary to produce TM steels, it was simply easier and less costly to make all their tubulars in the same way.

I truly abhore the one size fits all aspect to carbon steel making today when most X-42 pipe meets X60 pipe mechanicals. And more and more carbon steels are produced with fine grain melting when coarse grain steels would be better for the particular service.

 

[kingnero]

For me as long as it complies with 5L / 3183 I don't really care how they make it.

It's not about the way they "make" it (as in producing the steel), more of a question how they work with it afterwards (welding, bending, ...). There you will see the differences in execution quality!

Question more suitable for forum330: Metal and Metallurgy engineering?

This exact thread has been lingering there for about a month without any replies, so I asked the mods to move it here...

TM pipeline steels were developed by Japanese mills in the 1970s and a number of countries' mills eventually followed suit to provide low toughness proerties desired by ever more customers. With regard to circ seam welds weld procedure qualification on these TM tubulars proved that the HAZ met toughness requirements. It is more than likely that once mills had introduced the equipment necessary to produce TM steels, it was simply easier and less costly to make all their tubulars in the same way.

Thanks weldstan, it makes sense that the steel mills use a standard production process for all of their pipes. As I don't see a "technical" reasoning behind the use of TM steels, this is indeed a logical explanation. I was just hoping for a more technical reason apart this "we've always done it this way..." explanation
But it is indeed correct that the execution conforms to all the requirements (correct welding procedures yield indeed the required charpie values aso), so from a paperwork point of view, there is no reason to change. I'm just lying awake at night (as a figure of speech) because according to my humble opinion there are better/more efficient ways to work...

 

[SJones]

It's not only strength and toughness that drive steel design. Sour service performance requirements have grown steadily over the years impacting upon production techniques. Gas pipelines demand high toughness for fracture arrest that may be difficult to achieve without TMCP. And so on, and so forth. 'Decent' pipe mills won't hide behind stock answers, instead, they publish papers.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

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

 

[blacksmith37]

We did various testing of TMCP pipe starting with some Sumitomo X60 in the early 70's . I was always impressed by mechanical properties and weldability . I was on API Com. 5 in the 80's and 90's and don't remember hearing any complaints about TMC pipe.
And it is great for ERW pipe; excellent properties in the weld zone and very few/none stringers in the outbent fiber zone which so often causes failure of regular carbon pipe Also good for OCTG casing and tubing. I can't easily think of a reason to use N & T high carbon instead of TMCP but I have been retired 25 years

 

[weldstan]

Steve is so correct. Owner/Users dictated metallurgical and mechanical requirements of line pipe thru the 1970s and beyond and in order to compete with Japanese mills, other mills needed to follow suit. I could never quite understand US mills lagging behind. Two mills that I knew (one that I worked for) put hundreds of millions into their melting and casting facilities but omitted to upgrade their plate mills to make the TMC plate. Both went out of business in the 1980s.