There are no specific requirments in B31.3 for this. It's going to kick you back to design calcs for that. As for what normally effects.. normal doesn't come into the picture for LNG or any other cryogenic service. 3x base metal prohibition sounds like a stress analysis. B31.3 puts the monkey on design engineering, who has to provide this information to welding engineering who in turn has to see to it that it finds it's way to the WPS.
B31.3:2004
328.4.3 Alignment
(a) Circumferential Welds
(1) Inside surfaces of components at ends to be
joined in girth or miter groove welds ""shall be aligned
within the dimensional limits in the WPS and the engineering
design.""
(2) If the external surfaces of the components are
not aligned, the weld shall be tapered between them.
(b) Longitudinal Welds. Alignment of longitudinal
groove welds (not made in accordance with a standard
listed in Table A-1 or Table 326.1) shall conform to the
requirements of para. 328.4.3(a).
Regards,
Gerald