Branch connections under external pressure are covered in para. 304.3.6. The same rules described in Sections 4.4 and 4.5 are used. However, only one-half of the area described in Section 4.4, covering welded branch connections, requires replacement. In other words, only one-half of the area A1 requires replacement. Also, the thicknesses used in the calculation are the required thicknesses for the external pressure condition. #Little_PEng.