Could a piece of SA-106B pipe which has been in service for 10 years be rerated for another service with lower pressure and low temperature (-40°C) withought impact test using Fig 323.2.2B of B31.3 or API 579 should be used for this purpose?
Yes, it is possible provided the current condition of the pipe is evaluated, and a FFS evaluation for the new design conditions is performed using ASME/API FFS-1.
Correct; ASME B31.3 is a design/construction Code only. However, API-570 for in-service pipe refers back to it a lot. The *Official* Code(s) would be listed as API-570, ASME/API-FFS-1, API 579, etc., but you will predominately be working out of B31.3.