Differencies between ASTM A320 L7M and ASTM A320 L7 1

[Vinzzzz]

hi, to all.

I'm interested to know if there are differencies between ASTM A320-L7M and L7.I'm selecting bolts and nuts for Low Temp Valves. About their differencies i have found that L7 are mechanically better than L7M and also that L7M are in accordance to NACE requiremnts. Tis means that L7M can be considered NACE?

I have also noted, for example that comapny as Shell uses indistinctly for sour and not sour always ASTM A 320 L7M.

Thanks for all.

Best Regards Vincenzo

 

[CoryPad]

Both classes use the same chemical composition (C 0.4 - Cr 1.0 - Mo 0.25). The difference is that L7M is required to be tempered at 620 [°]C minimum, which reduces the mechanical properties, but improves toughness and resistance to embrittlement. L7M can meet NACE requirements for use in sour service.

 

[Vinzzzz]

Hi Cory,

Thanks for your help/explanation i want to attach a good document that i have found on web about Nace Stud Bolts Classes and API requirements in wich it is clear when the L7M or 7M is necessary instead L7 or 7 grades.

Nace after 1997 had eliminated the classes and now speaks only about h2s presence or not.
For these reasons the stud and bolt Classes 1 and 2 means the use of L7M and 7M grades while for the Classes 3 and 4 it is not necessary the use of a NACE material (h2s not present)so are suitables 7M and 7 grades rispectively for ASTM A320 and ASTM A194.

Thaks for all i hope that the attached document is usefull not only for me but to the other peopole.

With my best regards Vincenzo Saviello.