46 CFR §154.650

1. (a)Cargo tank and process pressure vessel welding must meet Subpart 54.05 and Part 57 of this chapter.
2. (b)Welding consumables used in welding cargo tanks must meet § 57.02-4 of this chapter.
3. (c)Independent tanks must meet the following:
   1. (1)Each welded joint of the shells must be a full penetration butt weld, except dome to shell connections may have full penetration tee welds.
   2. (2)Each nozzle weld must be of the full penetration type, except for small penetrations on domes.
4. (d)Each welded joint in an independent tank type C or in a process pressure vessel must meet part 54 of this chapter, except that any backing rings must be removed unless specially approved by the Commandant (CG-OES).
5. (e)Each welded joint in a membrane tank must meet the quality assurance measures, weld procedure qualification, design details, materials, construction, inspection, and production testing of components developed during the prototype testing program that are specially approved by the Commandant (CG-OES) under this part.
6. (f)Each welded joint in a semi-membrane tank must meet paragraph (c) or (e) of this section.