According to B16.34 there are 3 tables that define an acceptable casting, the tables are divided up by wall thicknesses . I am required to meet is Table I-1 for valves under 2" thick (page 100 in 2004 version). The table specifies gas porosity up to level 2, sand level 3, CA shrinkage lvl 2, etc.My customers refer to castings that meet this table as level 3 castings. What are the other levels based on? Is there a table for it, API-6D maybe? Any clarification would be great. Because every Xray tech I know just use the table in B16.34