Selection of material for minus temperature

[Pipingclassic]

Hi,
For carbon steel material, based on the curve in B31.3 we can use impact tested carbon steel pipe and other option to go for LTCS pipe material too.
but doubt is upto what limit we can go for Impact tested Carbon Steel material instead of selecting LTCS.

 

[metengr]

The range for impact tested pipe is based on material, design thickness and minimum metal temperature. Do you know how to use Figure 323.2.2A in B31.3 for exemption to impact testing?