ASME VIII Nozzle wall thickness (UG-45 or UW-16) 4

[Rafael Erler]

Dear colleagues,

I'm working for an inspection company and in order to get to know the ASME BPVC code I was required to perform an assessment in a air compressor equipment to check its construction compliance within the code.

This is a classical pressure vessel built with a cilindrical shell and two semi-spherical heads. There are two inspection openings located at the center of each head, connected by fillet welding.

Each opening has the same outside diameter (27.15 mm / 1.07 in) and the same wall thickness (4.05 mm / 0.16 in), so I assumed this is a 3/4" (DN 20) NPS pipe.

Paragraph UG-45 (Nozzle Neck thickness) tells me to calculate t_UG-45 = max(t_a,t_b), which is based on paragraph UG-27 and table UG-45. The result of t_a is something about 1.7 mm, but table UG-45 determines a wall thickness (t_b) of 2.51 mm for a 3/4" NPS size. Since the verified wall thickness is equal to 4.05 I can state that the equipment meets the requirements of UG-45, right?

It turns out that paragraph UW-16(Minimum Requirements for Attachment Welds at Openings) (f)(3)(-6) states the following: "In lieu of the thickness requirements in UG-45, the minimum wall thickness for fittings shall not be less than that shown in Table UW-16.1 for the nearest equivalent nominal pipe size.". Table UW-16.1 gives me a wall thickness of 4.2 mm which is way larger than 2.51 mm given by table UG-45.

I'm clueless about which of these two requirements I should use.
I'll be very grateful with any help on this!

PS: I'd like to stress out that these are inspection only openings.

 

[david339933]

There are special rules for fillet welded connections. You must follow UW-16(f)(3)(-6). This table basically has the thicknesses of 3000# cplgs. Which is what you have (.16") You are not getting the full strength of a full pen weld, and therefore a thicker neck is required...especially since there are no reinforcement calcs being done.

 

[SnTMan]

First, pipe is not a fitting.

Second, no way to tell from the OP if UW-16(f)(3)(a) is met in its entirety which it must be to apply Table UW-16.1.

Third, see second sentence, UG-45.

Regards,

Mike





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

 

[waliq]

@snTMan: I think the term "fittings" is a broader category. This includes pipes, reducers, flange fittings, bolting pads, elbows, tees etc.

UG 45 states that in case of access and inspection openings, t UG-45 is equal to ta. But, UW -16 (f)(6) does give a reference to UG-45 from which I understand that upto a fitting(be it a nozzle pipe too) size of NPS 3", minimum nozzle neck thickness is to be as per table UW-16.1 unless UG 45 calculations yield a larger thickness.

"In lieu of the thickness requirements in UG-45, the minimum wall thickness for fittings shall not be less than that shown in Table UW-16.1 for the nearest equivalent nominal pipe size."

 

[SnTMan]

waliq, UW-16(f) could encompass butt-weld fittings I suppose. Hadn't considered it. Thanks

Regards,

Mike



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

 

[wsmith22]

So I read "In lieu of the thickness requirements in UG-45..." as a 2000# fitting may be used with fillet welds if it is calculated per UG-45, even if it is less than the min. wall thickness shown in Table UW 16.1. If this correct?

For example, we typical weld threaded elbows to heads for drains. It gets confusing because the minimum thickness is less than the requirements of Table UW-16.1 for a 2000# elbows (per ASME B16.11). However, the band section that connects the elbow to the head is thicker than what is required by the table. This is the actual neck that will contain the fillet weld.

The "In lieu of the thickness requirements in UG-45" was added in the 2017 Edition.

 

[david339933]

So I read "In lieu of the thickness requirements in UG-45..." as a 2000# fitting may be used with fillet welds if it is calculated per UG-45, even if it is less than the min. wall thickness shown in Table UW 16.1. If this correct?

Not sure why you received a star....this statement is not correct. UW-16(f)(3)(-6) clearly states that Table UW-16.1 SHALL be the min. thickness rather than that calculated by UG-45.

Should add that if UG-45 min. thickness is larger than Table UW-16.1, I would use that.

 

[Rafael Erler]

Fellows, I'd to thank you for your support!

So, david339933 UW-16(f)(3)(-6) tells us to consider table 16.1 for min thickness. I know this question might sound dumb for you, but what is exactly the point of UG-45? For which kind of nozzles I should apply UG-45? Non welded Nozzles? If so, maybe UG-45 should be revised to add a mention that it is no applicable to welded nozzles.


Best regards.

 

[david339933]

In your OP you stated you assumed it is pipe....is it pipe?..is it flanged? I assumed a cplg as pipe is not allowed by this paragraph, and you referenced UW-16(f)(3)(-6). As SnTman stated....UW-16(f)(3)(-6) is not applicable to pipe...only ASME Standard Fittings. For pipe you must use UG-45, and cannot attach by fillet welds on the outside only...unless the requirements of UW-16(e) are satisfied.

 

[david339933]

And there are no dumb questions....that is the point of this forum!

 

[Rafael Erler]

David339933,

My bad! It is not a pipe; it is a threaded welded connection with an equivalent OD of a 3/4 NPS pipe (attachment).

https://files.engineering.com/getfi...18-bf0f-2bf43ad05919&file=20190213_112226.jpg

Thanks again for your help!


Best regards

 

[SnTMan]

Rafael Erler, Since UG requirements are general while UW applies to welded construction, normally UG-45 would have precedence over any connection thickness rules in Part UW, or other Parts as well. Notice the title. Notice UW-16 in general contains no rules as to required connection thickness. Notice only UW-16(f)(3)(a) contains rules overriding UG-45 and only for a particular type connection. This connection must meet all requirements (-1) thru (-5) to apply (-6). Failing any of that, you are back to UG-45.

Also note that many consider ASME to stand for Always, Sometimes, Maybe, Except

Regards,

Mike



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

 

[r6155]

Rafael Erler
Are you sure that are semi-spherical heads?
Why “I assumed this is a 3/4" (DN 20) NPS pipe” ?. Where are the drawings and design calculations?

Regards
r6155