Comparing ASTM A333Gr6 and API 5L X52N PSL2

[HJS7]

ASTM A333Gr6 seamless pipe, CVN 14 / 18 J at -50°F / -45°C, is available up to 24”. Above the 24” ASTM A333Gr6 welded pipe is available. As alternative API 5L X52N PSL2 welded pipe is prescribed often. At material certificates we find both standards with material descriptions also.

Comparing ASTM A333Gr6 with API 5L X52N PSL2 standard we find differences in yield strength, tensile strength, chemical requirements and (standard) impact requirements.

Why is API 5L X52N an alternative for ASTM A333Gr6 instead of a lower API 5L grade? I’ve been told the larger amount of carbon in a steel, the more negative influence at the low temperature physics, e.g. CVN test, of this steel.
Isn’t it easier to made less brittle steel out of material with a lower amount of Carbon?

Thank you,

HJS

 

[metengr]

There is a balancing act between notch toughness (impact) and strength properties of steels. In general, as the carbon content is increased the strength properties increase, however, notch toughness decreases.

So, lower carbon versions may have increased notch toughness but have lower mechanical properties, like tensile and yield strengths, which may not suffice for ASTM A333 Gr 6 material.

 

[SNORGY]

The link may be of interest.
Depending on Code Of Construction, from the point of view of "toughness" alone, API 5LX 52 PSL2 might indeed be an acceptable substitute for A 333 Gr 6 in certain cases, but the reverse would not be true if examination of the DWTT or CVN fracture surface are of interest. To my knowledge there is no examination of the fracture surface when qualifying material to A 333 Gr 6.

http://www.pipemag.com/publications/journal/currentSample/JPE June 2010 - sample issue.pdf

 

[SJones]

The base Charpy test temperature for the API pipe is 0 deg C. -46 is not overly onerous, but it would most probably cause pipe mills to alter their target chemical composition dependent upon the dimensions of the pipe. Chemical composition requirements are generally maxima which means that the composition isn't actually forced to the values reviewed.

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.

 

[HJS7]

Thank you for your comments.

When ASTM A333Gr6 is prescribed, because the impact values are mandatory, probably we can order API 5L PSL2 pipe according para 9.8.2.1 of this API 5L standard with impact tests at low temperature.
If we have a look at the yield- and tensile strength in the API 5L standard, we find these values of API 5L GrB, X42 and X46 equal or higher than the ASTM A333Gr6 yield- and tensile strength values.
So why is API 5L X52 an equivalent for ASTM A333Gr6 and not API GrB, X42 or X46?

Thank you,

HJS