NBIC Part 3 PWHT

[stephenbell50]

For a nozzle in an ASME Sec. VIII Div. 1 2:1 semi ellip. head:

I have a question about how "R" is defined in the Heating Band definition in section 2.5.2 of NBIC 2015 Part 3

Heating Band (HB) – this is the region that encompasses the application of heat for PWHT and is
defined in length by the equation, SB + 4*sqrt(R*t)where R is the outer radius of the spherical or
cylindrical shell in inches (mm), and t is equal to the nominal thickness of the spherical or cylindrical
shell in inches (mm).

Is R the spherical radius of the head?

 

[GenB]

Read yr own post. Where R of the outer of the shell or head... ir half O.D. gen blr

 

[metengr]

Yes, R is defined as the outer radius for the application of PWHT under NBIC, Part 3.

 

[stephenbell50]

So R should be 0.9*D where D is the ID of the vessel/head. The spherical radius of a 2:1 semi ellip is 0.9*D...

Next question in that same equation HB = SB + 4*sqrt(R*t):

Is the SB in that equation just t or 2" (whichever is less) or is it supposed to be the nozzle OD + 2 times t or 2"?

I guess the reason for this question is I'm not sure whether the equation is calculating the radius or the diameter of the HB. The figure 2.5.2-b shows all the dimensions as diameters.

Thanks

 

[racookpe1978]

No.

R MUST ONLY be defined based on the OD and the thickness of the vessel, at the relevant location of the weld.

NOT the ID. Thus, you can approximate the R_calc = (0.9*ID + Twall). Alt: 0.9*(ID + Twall) which is slightly less.

Not 0.9*ID.

 

[metengr]

The Soak Band (SB) shall extend tangentially and radially
from the edge of the nozzle wall, or attachment weld or repair area equally by a minimum distance as
defined by the thickness of the shell, t or 2 in. (50 mm), whichever is less. See Figure 2.5.2 b).

 

[stephenbell50]

I just noticed something strange between the 2013 NBIC Part 3 and 2015 NBIC Part 3 for the equation in section 2.5.2

2013 edition: HB = SB + 4*sqrt(R + t)

2015 edition HB = SB + 4*sqrt(R * t)

there is a huge difference between these equations. I have seen metengr posts on this section of NBIC Part 3 so would like to know his thought on this.

 

[metengr]

It was an editorial correction. It should be Rxt under the square root sign.