VIII-1 Table UW-16.1

[Cobra17]

I have a manufactures standard fitting that is attached with a single fillet weld from the outside and meets all the requirements of UW-16(f)(3)(-a)

NPS = 3/4" (ID of 1.05")
OD = 1.438"
Wall = 0.194"

the fitting passes internal pressure requirements, weld sizes, etc.. but fails UG-44 thickness check based on Table UW-16.1

If I'm reading UW-16(f)(3)(-a) and table UW-16.1 correct.

I use my fitting OD to determine my minimum wall thickness per table UW-16.1

Per the Notes of Table UW-16.1

GENERAL NOTE: For fittings having a specified outside diameter
not equal to the outside diameter of an equivalent standard NPS
(DN) size, the NPS (DN) size chosen from the table shall be one having
an equivalent outside diameter larger than the fitting’s outside
diameter.

OD= 1.438" therefore, I use NPS 1.25 (1.660" OD), so my minimum wall thickness must be 0.30"

However, if I use a standard B16.11 3/4" coupling (1.38" OD) my wall thickness is only 0.16". And if you were to 'pretend' a B16.11 3/4" coupling was a manufacturers standard it would also require a 0.30" wall.

what it not make more sense if the note read:

GENERAL NOTE: For fittings having a specified INSIDE diameter
not equal to the outside diameter of an equivalent standard NPS
(DN) size, the NPS (DN) size chosen from the table shall be one having
an equivalent outside diameter larger than the fitting’s INSIDE
diameter.

 

[IdanPV]

Hi Cobra17,


Many pressure vessels manufacturers making custom couplings (fittings/nozzles), the Code committee decided to document what the minimum should be.

Table UW-16.1 is actually a dimension from ASME B16.11 class #3000 threaded coupling.
Therefore, for NPS 3/4 you should use ASME B16.11 Table I-5 - O.D=1.38".
Assuming you are referring to an NPT threaded fitting the Major diameter of the thread is from ASME B1.20.1 Table 2 (NPT Thread) - 1.05" (which is equal to B36.10 O.D)
Thickness = (1.38-1.05)/2=0.165" which meets Table UW-16.1 requirements.

This LinkedIn article may be helpful:

https://www.linkedin.com/pulse/actu...se-article_more-articles_related-content-card

 

[Cobra17]

IdanPV,

My point was that as the wall thickness increases (ID staying the same), according to table UW-16.1, the note tells you that you need to increase the minimum wall thickness because it's based on the OD of fitting

I have a 3/4" NPT fitting, like B16.11 but the OD is larger so its not a B16.11 coupling. Yes the table says MINIMUM, but the Note says something else. Based on the Note in table UW-16.1, a 3/4" B16.11 coupling would be considered NPS 1-1/4, except it's not because it's based on the NPS.

and the committee did a terrible job of documenting the minimum, table UW-16.1 is rounded to 2 decimals from B16.11 which forced Code Case 3035.

 

[IdanPV]

Cobra17,

a. Is that a 1.438" circular bar material that need to be machining into threaded fitting?
b. Which thread NPT\BSP?

 

[Cobra17]

It's a forging (SA-105) with 3/4" NPT

 

[IdanPV]

@Cobra17,
I know it is been a while since you posted it,
Did you consider to use Code Case 3035?
It stated that the thickness of the fitting shall not be less than the thickness of B16.11 #3000 threaded coupling.
It also stated that the thickness of of socket weld coupling is also acceptable.

The closest O.D of B16.11 coupling is NPS 1 with O.D of 1.75", the min. thickness required is 0.2"