Understanding of PWHT thickness in B31.3

[mariolucas75]

Dear Forum members please help me to understand what is control thickness in PWHT.

Asme B31.3 edition 2014 says:

"The term control thickness as used in Table 331.1.1
and Table 331.1.3 is the lesser of
(1) the thickness of the weld
(2) the thickness of the materials being joined at
the weld or...."

Then it explains what is the thickness of the weld:

"Thickness of the weld, which is a factor in
determining the control thickness, is defined as follows:
(1) groove welds (girth and longitudinal) — the
thicker of the two abutting ends after weld preparation,
including I.D. machining"

So what does it mean then if i put definition of thickness of the weld into the first statement:

"The term control thickness as used in Table 331.1.1
and Table 331.1.3 is the lesser of
(1) the thicker of the two abutting ends
(2) the thickness of the materials being joined at
the weld or...."

I am confused between these two points... so the control thickness is thicker of two members being joined or thinner (lesser)... ???

Thank you very much

 

[KevinNZ]

The first term is the thickness of the material and second the thickness of the abutting end. They are not the same thing when there is taper down to the weld.

 

[DekDee]

Kevin,
Have to disagree.
Thickness of the weld (based on your drawing) is No. 2 on the left side.
Thickness of the weld for PWHT calculations is always the thickness at the weld (for groove welds) - irrespective of the material thickness elsewhere.
If we look at your drawing and hypothetically say the material on the left is 20 mm thick, machined down to 15 mm thick and then welded to 10 mm thick.
The thickness of the weld is 15 mm thick.
If it was machined down to 10 mm the thickness of the weld is then 10 mm.
The "controlling thickness" is then either 15 mm or 10 mm.

(2) the thickness of the materials being joined at
the weld or the thickness of the pressure-containing
material if the weld is attaching a nonpressurecontaining
material to a pressure-containing material.

This relates predominantly to branch welds or attachment welds.

Trying to look after a 2 yr old at the moment so no time for detailed explanation,
Cheers,
Shane

 

[KevinNZ]

DekDee

I think we actually agree. I did not say when to use weld, abutment or material thickness the code covers that as per your post. Note my (1)s and (2)s on the sketch are not the same as the code (1)s and (2)s.

 

[DekDee]

My apologies Kevin - misunderstood your drawing.
Cheers,
Shane