Refer to the below Interpretation, its apply to Figure PW-16.1(z) but I assume that you can draw conclusions from it regarding your case as well
Standard Designation: BPV Section I
Edition/Addenda: 2010
Para./Fig./Table No: PW-39, Table PW-39-3, Figure PW-16.1(z)
Subject Description: Section I Inquiry, PW-39, Table PW-39-3, Figure PW-16.1(z), Postweld Heat Treatment Requirements
Date Issued: 03/19/2013
Record Number: 13-264
Interpretation Number : I-13-09
Question(s) and Reply(ies):
Question 1: Are the tube to header welds illustrated by Figure PW-16.1(z) considered circumferential butt welds??
Reply 1: No.
Question 2: Do the postweld heat treatment exemptions for circumferential butt welds noted in Table PW-39-3 apply to the welds illustrated by Figure PW-16.1(z)??
Reply 2: No.