PWHT Pipe Supports

(b) In the case of fillet welds at slip-on and socket
welding flanges and piping connections DN 50 (NPS 2)
and smaller, for seal welding of threaded joints in piping
DN 50 and smaller, and for attachment of external nonpressure
parts such as lugs or other pipe supporting
elements in all pipe sizes, heat treatment is required
when the thickness through the weld in any plane is
more than twice the minimum material thickness requiring
heat treatment (even though the thickness of the
components at the joint is less than that minimum thickness)
except as follows:
(1) not required for P-No. 1 materials when weld
throat thickness is 16 mm (5⁄8 in.) or less, regardless of
base metal thickness.


I underlined the answer to question 1.
2. Not necessarily, if the fillet weld joining the supports to the pipe OD is below nominal thickness exemption for PWHT.
3. This means any imaginary line drawn through the cross section of the weld joint to establish deposit thickness.