1. Spot radiography is an aid to quality control where the code does not require a weld to undergo full radiography (100%) . You can make reference to ASME VIII Div 1 UW-11. Acceptance criteria is UW-52
2. ASTM A 516 material is Carbon Steel Pressure Vessel Plates for Moderate and Lower Temperature Service.
3. There is no difference between SA516 Gr 70 and A516 Gr 70 materials. The difference is only in the Grades. ie Gr 65 is different from Gr 70