6 For that part of a vent pipe exposed to weather, pipe wall is to be as specified in 4-6-4/9.3.2(a).
7 The thickness indicated for sounding pipes is for the portions outside the tanks to which the pipe is opened. Within bilge well, to which the pipe is not opened, the thickness is to be extra-heavy; see 4-6-4/11.3.3iv).
8 For bilge pipes, column D thickness applies only where required by 4-6-4/5.3.4(c).
9 Where permitted by 5C-1-7/3.3.3 and 5C-1-7/5.3.2 of the Steel Vessel Rules.
10 For nominal sizes larger than 450 mm (18 in.), the minimum wall thickness specified for 450 mm (18 in.) nominal size pipe is applicable