UW-16(f)(2) exemption

[4xeng]

Hello all,

Consider a case where a standard 1"-6000# threaded coupling is being attached to a pressure vessel by outside and inside fillet welds only. It can be attached using figure UW-16.1 sketch (y-2).

However, I am using exemption UW-16(f)(2) and using minimum fillet weld sizes. To use that exemption it is required that weld strength calculations as per UW-15(a) are performed. This fitting is also exempt from reinforcement area calculations as per UG-36(c)(3)(a). Does that relieve me from calculating UW-15(a) calculations (that were required by UW-16(f)(2) exemption) by using UW-15(b)(2)?

I have a case where I can use 3/16" fillets by using UW-16(f)(2) exemption. and not perform the UW-15(a) weld calcs as exempted by -15(b)(2). However, if I do perform the weld calculations that fillet size fails.

Please let me know what you think of using exemption from UW-15(b)(2) to override the requirement of UW-16(f)(2)(-a).

Thanks in advance.

 

[IdanPV]

Refer to UW-15(b)(2), it give the exemption only for several attachment methods (Figure UW-16.1 sketches). Not for all.

 

[SnTMan]

UW-15(b)(2) seems clear to me. Forget the strength calculations.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[IdanPV]

Read it once again.
UW-15(b)(2):
"(b) Strength calculations for nozzle attachment welds for pressure loading are not required for the following: (1) Figure UW-16.1, sketches (a), (b), (c), (d), (e),(f‐1), (f‐2), (f‐3), (f‐4), (g), (x‐1), (y‐1), and (z‐1)"

While UW-16(f)(2) stated that:"(2) Fittings not exceeding NPS 3 (DN 80) shown on Figure UW-16.1, sketches (x), , (z), (aa), and (bb) may be attached by welds that are exempt from size requirements with the following limitations:
(-a) UW-15(a) requirements shall be satisfied for UG-22 loadings.

So, it is pretty much depends on the attachment method you choose.

 

[4xeng]

IdanPV,

I am attaching the nozzle using (y-2) with size exemption. I understand that it is not listed in UW-15(b). But I am asking about exemption UW-15(b)(2). I know -15(b)(1) does not apply.

 

[marty007]

I think you still have to perform the UW-15(a) calculations, I don't think you can use the UW-15(b)(2) exemption in this case.

 

[SnTMan]

After a more careful read of both the Original Post and the Code ('17 Ed) I believe my previous reply was in error. I think if exempting weld sizes per UW-16(f)(2) then UW-15(a) is mandated.

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[IdanPV]

4xeng,

take a look at the sketches which exempt from the UW-15(a) calculations, for example:
(y-1) vs. (y-2) or (z-1) vs. (z-2) can you spot the difference?
(y-2) & (z-2) are just double fillet weld (parial penetration) while (y-1) or (z-1) are more like butt weld (full penetration)
"The Code philosophy" is that nozzles which attached by butt welds are less dangerous than these with fillet welds, that's why UW-15(a) calculations are mandatory for (y-2) attachemnt method.

By the way, why don't you use UW-16(f)(3) instead?

 

[r6155]

IdanPV, you are wrong

(y-2) is double fillet weld (not partial penetration)
(x-1),(y-1) & (z-1) are full penetration and fillet weld
(z-2) is partial penetration and fillet weld
(f-1) to (f-4) are butt welds

Can you spot the difference between full penetration and butt weld?

Regards

 

[IdanPV]

r6155,

I think that my post wasn't clear. And you are right.
These methods (x,y,z-1) are not butt weld in any way. They just full penetration.
But, that's what gave these kind of attachement methods the exemption from UW-15(a) calculations and that's what I was trying to say.

Thank you.

 

[SnTMan]

Might be interesting to know what value of "tmin" is applied to the OP's design...

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[r6155]

SnTMan
To determine the thickness of couple See ASME B16.11 (2016)
6.3 Threaded Fittings
6.3.1 Wall Thickness. The body or end wall thickness
of threaded fittings shall be equal to or greater than the
minimum values, G, as shown in Tables 3 through 5 or
Tables I-3 through I-5.

Table 3 is for Threaded Elbows, Tees, and Crosse, but not for coupling.

Options
1) Determine the thickness of coupling = (OD of coupling – OD of pipe) /2

2) Use Table 3

3) Work with B1.20.1 Pipe Threads ..to obtain root thread diameter at the small end of internal thread

Option 1) is conservative and easy to use with computer programs, and no waste time working with tables.

Always engineering judgment is required.

After this and with shell thickness of the vessel, not mentioned by (OP), we can obtain the value of “tmin” , finally the dimension of fillet weld.

Hope it help

Regards

 

[IdanPV]

Hi r6155,

Is that the procedure to determine "t-min" as described in UW-16(b)?
Where did the refernce to B16.11 come from?
The only reference to B16.11 is in UW-16(f)(4), to define "t-w".

The Code only stated that "t-min" is equal to the smaller of 3/4 in. or the thickness of the thinner of the parts joined by a fillet, single-bevel, or single-J weld.

Why don't use the actual nozzle thickness? ("...thickness of the thinner of the parts"
Or, why don't use B16.3 Table 8 instead?

 

[SnTMan]

r6155, yes, all true but it does not furnish "tmin" for the OP's design.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[r6155]

@IdanPV
ASME B16.3 is not included in ASME VIII.
See B16.11 in UG-44
Figure UW-16.1 (y-2) is fillet weld only, not “tw”
Remember firs post of 4xeng (OP). We must find the thickness of couple NPS 1 Class 6000, but in B16.11 Table 5 is not showed: use the options that I mentioned.

@SnTMan
Why not?
We need to define “t1” or “t2” of fillet welds in sketch (y-2)
Suppose shell thickness = 10 mmm and couple is 12 mm thickness.
tmin= 10 0,7 x 10= 7 mm and the smaller is 6 mm for “t1” or “t2”

Regards

 

[SnTMan]

But suppose the coupling is as thin as permitted by Table UW 16.1, 5.5 mm. Which is it?

In any case 0.7 tmin is likely to be larger than 2.5 mm. UW-15(a) required it seems.

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[4xeng]

Hi IdanPV,

I am aware that the attachment (y-2) is not included in exemption UW-15(b)(1). I am talking about UW-15(b)(2) exemption. The opening is exempt from reinforcement calculation because of finished diameter less that 2-3/8”.

Would that exempt me from UW-15(a) calculations even when UW-16(f)(2)(a) specifically ask for it?

Thanks

 

[4xeng]

I saw the replies by Marty007 & Stnman. That's what I think as well.

Thanks!