UG-11(c)(1) When is standard fitting be considered as modified / non-standard?

[balamurugan02]

Dear gents,

I'm designing a Vertical separator which is fully made out of ASME standard fittings (12" NB - Sch.100) which has an equal tee as part of the shell. The tee has a 2" NB nozzle opening, so does this mean that the equal tee is considered as modified [not covered under UG-11(c)(1)]?
If it is not covered under UG-44 & UG-11(c)(1), should the tee branch be considered as an opening in the shell and be backed by reinforcement calculation? My AI's suggestion is to just perform the calculation for pressure-temperature rating (thickness calculation considering the fitting as a straight pipe, which is also a prerequisite in case of UG-44 applicability for ASME B16.9 fittings). below snap for your reference

 

[mk3223]

Per size and construction, IMO, the Separator is a pressure vessel and should follow the Code construction for all the components, including the reinforcements of nozzles and openings, support, etc.

 

[XL83NL]

MK, the OP mentioned his design follows VIII-1. What’s your point?

Interesting question bala. I don’t have the code at hand but some additional calcs are required I believe. Other codes such as the B31’s follow the practice in this regards. Which one(s) and acc. which section(s) I don’t know, but like to know as well as this question has often puzzled me.

 

[SnTMan]

balamurugan02, I can't exactly answer your questions, but make a few observations:

1) I doubt it can truly be considered a standard fitting after adding the 2" connection.

2) Apparently no provision under B16.9 for the additional opening in the tee. Perhaps some provision exists under a piping Code B31.x, which could be introduced under U-2(g).

3) Under Sec VIII, Div 1, the 2" connection is likely exempt from reinforcement calculations.

4) Under same, the branch would be treated as a large opening. Apx 1-7 is not applicable, Rn / R > 0.7. You'd need a U-2(g) approach.

5) Notwithstanding 1) above, if your AI's approach would make all the interested parties happy, I'd likely go with it, assuming the service is not "severe". No definition offered

Regards,

Mike


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

 

[balamurugan02]

MK, the design and construction of the vessel is based on Sec VIII Div-1

XL, B31.3 has provisions to calculate reinforcement for welded branch connections but does that apply here since it isn't a welded connection, moreover B31.3 doesn't outline any limitation of d/D ration, not that I know of.

SnTMan, thanks for your insights, as you mentioned the 2" NB opening is exempted for additional reinforcement, My AI's approach is that if the Tee complies to the ASME B16.9 (proof pressure tested as per ASME B16.9) it shall be deemed adequate for our design internal pressure, but I'm having a hard time convincing my client. If suppose I had to do the calculation for that branch, I'd also have to evaluate the load (wind, reactions & moments due to other nozzle loads) at that junction, so performing FEA is my only option, I guess.

 

[XL83NL]

bala, that wasnt my point. My reference to the B31 codes was emrely meant to point out thety follow the same apporach when it comes to using fittings acc. listed standard (such as B16.9), uisng the straaight seamless pipe approach for their p,T-rating. Now, since you modify the fitting, the B31 codes follow a similar approach for that alteration, however, as example B31.3 then points to 304.7.2. In your case, luckily Is day, you have VIII-1, which is a bit broader on engineering techniques for such alteration. I believe there's a section (or multiple set of section) in VIII-1 that will help you, I djust know which ones, as this question has puzzled me sometimes as well.

Have you looked up if there's an interpretation on this subject?

 

[balamurugan02]

XL, as SnTMan mentioned, VIII-1 doesn't cover this issue due to the limitation on Rn/R ratio. I've searched the "ASME Interpretations Database" on "UG-44 & UG-11", interestingly there is not a single query on the use of Tee's with nozzles under UG-44, but on a similar case for 'B16.9 Cap with nozzle' ASME replied that, "calculation for reinforcement of the nozzle and P-T rating of the Cap should be performed". But in our case the main question is "whether P-T rating itself is enough or not". Thanks.

 

[XL83NL]

Well, the analogy to B16.9 is quite same, isnt it? You modify the fitting, by cutting a whole, adding a nozzle, welding them together. You can still, and I think quite easily, perform a calculation showing that the 2" opening is sufficiently strong, or not, and whether it meeets your preferred p,T-rating.

 

[balamurugan02]

XL, no its not the same my query is regarding the branch on tee itself anyway we've raised this query to ASME. I'll update upon their response in the mean time if anyone has faced the same issue kindly share your experience.

 

[XL83NL]

I think that from a Code perspective, adding a nozzle to a B16.9 cap is the same as what youre doing now. I guess I didnt phrase that part of my reply too clear.
However, we never seem to relize this as people make holes in B16.9 all the time, and we have accepted this as standard practice. Nevertheless, the rationale on what to do then with the calculations, from a Code perspective, would still be the same I believe.

 

[CuMo]

If it were me, I would at least do an internal/external (whichever is relevant) pressure calculation
for the cylindrical portion of the Tee and then check the reinforcement of the 2" fitting.
As mentioned above - it might be exempt from a reinforcement check.
I think you have to be careful about the weld proximities. If you're welding this fitting as set-in nozzle
then its weld prep and the circ seam prep of the reducer might get pretty close together and even merge.

 

[balamurugan02]

CuMO, as mentioned earlier those calculations were performed already and the vessel will undergo PWHT so overlapping of HAZ b/w welds are not an issue here. Thanks!

 

[XL83NL]

bala, just out of curiosity/interest, that picture from your OP, is your vessel drawn in flat (2D) AutoCAD, or some other program?

 

[BJI]

"I'd also have to evaluate the load (wind, reactions & moments due to other nozzle loads) at that junction" The designer is always required to address all loads.

When you modify a standard fitting, it is no longer covered by the PT rating and needs to be suitably designed (just like any other standard fitting). This is not a piece of straight pipe, you are putting a hole through reinforcing effectively. If you ever run analysis on a BW branch to see if meets reinforcing requirements then typically they fail, but are acceptable for the rating determined by proof testing, under the conditions it was tested (without the hole). Since it is not straight pipe and you are in the vicinity of a discontinuity, I don't believe it falls under exemptions for un-reinforced openings. If there is sufficient reinforcing in the nozzle neck alone to replace the area removed, then I guess you could justify that you have not weakened the standard fitting.

 

[balamurugan02]

XL83NL, drawn in good old "AutoCAD"

 

[balamurugan02]

BJI, Thanks! We decided to proceed with FEA anyway.