PetroStreet

Dear friends ,
I have a doubt in the governing thickness for PWHT for two
different codes i .e. ASME Section VIII Div- 1 and ASME B 31 .3 .
ASME B 31 .3 :
In Chapter V , as per clause 331 .1. 3 " When components are joined
by welding, the thickness to be used in applying the heat
treatment provisions of table 331 .1. 1 shall be that of the THICKER
component measured in the joint "
ASME Section VIII Div -1 :
As per Clause UW- 40 ( f) (5 ), The term nominal thickness thickness
of the welded joint as defined below When a welded joint
connects parts of unequal thickness, the nominal thickness as
used in tables UCS - 56 , UCS - 56 .1, UHA- 32 and UHT- 56 , is the
THINNER of two adjacent butt welded parts including head to
shell connections .
Now ,
Case- I : I have to weld the 02 pipes having 18 mm and 42 mm
thickness and my construction code is ASME B 31 .3. Both pipe ID
have been matched from inside by providing 1 :3 taper at thicker
pipe . Now shall I have to carry out PWHT or not? Per my view : as
per B 31 .3, PWHT shall be carried out .
Case- II : I have to weld the 02 plates having 18 mm and 42 mm
thickness and my construction code is ASME Section- VIII Div- 1.
Both plates have been matched from inside by providing 1:3
taper at thicker pipe . Now shall I have to carry out PWHT or not ?
Per my view : as per ASME Section Div- 1, PWHT shall not be
carried out .

I am considering the case for P.No. 1 material.
Governing thickness as per ASME B31.3:
Thicker measured in the joint would be 18 mm - PWHT Not required
Governing thickness as per ASME Sec. VIII Div. 1:
Thinner of the two parts joined by welding would be 18 mm - PWHT Not required

Hope this clarifies.

1. Have you given any straight length in the thicker portion as ASME Sec. VIII suggests?
2. And for piping have you tapered directly from the joint edge or given a straight length first then made a taper?
Actually, if the HAZ area adjacent to weld joint is coming within the qualifying thickness for PWHT, you have to perform it. It depends how have you tapered. If the straight lengths have been given and HAZ accommodated in this this straight length having thickness < qualifying thickness for PWHT, you do not need to perform PWHT then. Apply this simple concept for both cases and this is the basic theory behind defining the governing thickness.