46 CFR §56.30-5

1. (a)General. Welded joints may be used for materials for which welding procedures, welders, and welding machine operators have been qualified in accordance with part 57 of this subchapter.
2. (b)Butt welds—general. Butt welds may be made with or without backing or insert rings within the limitations established in § 56.70-15. When the use of backing rings will result in undesirable conditions such as severe stress concentrations, corrosion or erosion, then:
   1. (1)The backing rings must be removed and the inside of the joint ground smooth, or
   2. (2)The joint must be welded without backing rings, or
   3. (3)Consumable insert rings must be used. Commonly used types of butt-welding end preparations are shown in ASME B16.25 (incorporated by reference; see § 56.01-2).
   4. (4)Restrictions as to the use of backing rings appear for the low temperature piping systems and should be checked when designing for these systems.
3. (c)Socket welds. (Modifies 127.3.3A.)
   1. (1)Each socket weld must conform to ASME B16.11 (incorporated by reference; see § 56.01-2), to applicable standards listed in table 2 to § 56.60-1, and to Figure 127.4.4C in ASME B31.1 (incorporated by reference; see § 56.01-2) as modified by § 56.30-10(b)(4).
   2. (2)Restrictions on the use of socket welds appear in § 56.70-15(d)(3) for Class I service and in § 56.50-105 for low temperature service. See § 56.70-15(d)(4) for Class II service.
4. (d)Fillet welds. The size of a fillet weld is determined as shown in Figure 127.4.4A of ASME B31.1. Fillet-weld details for socket-welding components must meet § 56.30-5(c). Fillet-weld details for flanges must meet § 56.30-10 (see also § 56.70-15(d)(3) and (4) for applications of fillet welds).
5. (e)Seal welds. Seal welds may be used but must not be considered as contributing any strength to the joint.