Since this is the storage tank forum it should be API 650, API 620 or similar. If this is a pressure vessel question it should be posted in another forum.
For an API 650 tank, your shell material is in Group VI.
Per API 650 section 5.7.4 thermal stress relief (PWHT) is required for all flush-type fittings for any shell thickenss and PWHT is required for your tank for all openings over 2" NPS when the tank shell is more than 13mm [1/2"] thick.