UG-44 and flange external loads 7

[OnG_Engr]

All,

I've been addressing the changes in UG-44 regarding flange external loads by designing said flanges to Appendix 2. It has been strongly suggested that instead we just put in the quote and on the drawings, in large font, that the flanges are designed for zero external loads and it is the Customer's responsibility to brace their piping. Since UG-44(b) says "External loads MAY be evaluated..." instead of "SHALL be evaluated", I can't see a Code reason why we can't call out zero end loads and put it on the Customer.

Is just putting zero flange loads in the quote and on the drawing sufficient? Something doesn't feel right...

 

[TGS4]

That's just not practical to assume zero loads. Use the method in UG-44(b) to evaluate your customer's loads. If those don't work, then negotiate reasonable loads.

Do NOT evaluate your standard flanges with Appendix 2. That's not what it's for.

There are other methods out there for evaluating external loads on flanges. UG-44(b) was never intended to be the be all and end all in external loads. If there is another method that you have, and can convince your AI that it is acceptable, then go for that, too. Experience with comparable addictive may be be acceptable to your AI.

 

[OnG_Engr]

TGS4

I didn't evaluate a B16.5 flange using Appendix 2. I designed an Appendix 2 flange with extra "meat" that will mate to a B16.5 flange and used rigidity.

Let me rephrase my last question: Is just putting a minimal flange end load that's convenient to me in the quote and on the drawing sufficient?

 

[KevinNZ]

A low maximum flange load on your drawing/quote may help you but not useful to the purchaser. If the purchase knows what they doing they should be providing the flange load limits. If they purchase with a low limit and later find it can not be achieved then everyone has a problem.

why not ask the purchaser to provide the loads.

 

[OnG_Engr]

KevinNZ,

You're hitting on my problem: The purchaser does not know their flange loads. In fact, they cannot know the loads because they buy the big vessels before they lay out their piping. They don't even know that this is important to the vessel fabricator. Unfortunately, about half the time I cannot get feedback from the Customer to even discuss the issue as they just want price and delivery. My approach has been to go conservative and design to API 660. The Boss wants me to just put a minimal value in the quote and on the drawing, but ONLY IF there is not a rule somewhere that says you can't. My instinct says there's a good chance such a rule exists, even if it's indirect (e.g. something in 49 CFR 192 instead of Section VIII).

Let's put this another way: I'm looking for a rule that says I have to use something like API 660 end loads in the absence of Customer provided loads. Does anyone know of such a rule?

 

[SnTMan]

Worms de-canned

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

 

[r6155]

See API 660 Table 2—Nozzle Allowable Forces and Moments at the Nozzle Neck to Shell/Channel Interface.

Regards

 

[mskds545]

It sounds like using zero load would meet the requirements of your contract, but be aware that it might not lead to repeat business.

API 660 is reasonable, but if it's leading you to beef up flanges at your own expense, pick something lower and inform your customer of the rating. Reduce the API 660 loads uniformly by 0.75 or 0.5 or whatever works without changing the design and without taxing yourself with too many iterations. If the customer wants to pay for higher loads, take the money and use the Appendix 2 flanges (although making an Appendix 2 flange that mates to a standard flange to meet piping loads does not make a lot of sense to me...either both sides of the set are okay or neither side is).

Instead of picking one set of loads, you could put the equation in UG-44(b)(4) on the drawing, assuming the other requirements of UG-44(b) are met. This provides your customer with maximal flexibility when they lay out their lines. If you're feeling helpful, you could make a table by flange diameter and multiply out G, Pr, Pf, and Fm for them, giving them a limit of 16Me + kFe for each flange size. You would also need to make sure the shell can handle that range, which leads to a lot of paperwork if you have a lot of different nozzle arrangements. So it's something a customer might appreciate, but the should not really expect to get it for free.

-mskds545

 

[r6155]

Five minutes of calculation for each nozzle does not influence the total manufacturing cost.

Regards

 

[jtseng123]

Zero load is impossible and not practical at all.
The purpose of UG-44(b)is to limit the external bending moment and tensional force such that flange will not leak at the face of flange. No one can foresee what loads are except only knowing (flange rating -MAWP) is. So you will be better by putting { Equivalent pressure converting from external loads at the "FACE OF FLANGE" shall not exceed (flange rating table-MAWP) }

In my opinion, UG-44(b) shall be part of pipe stress engineer's work when they running CAESAR II. UG-44(b) shall be part of B31.3 and programmed into CAESAR II because there are hundreds of thousands of flanges that pipe stress engineers are dealing, and only a few on the vessel nozzles. And since the nozzle mating flange is B31.3 and stress analysis is done by pipe stress engineer, and they have to take care of flexibility to ensure hundreds of thousands of flanges will not leak, why shall it become vessel engineer or vessel fabricator to check ? not making sense at all.

Back to opinion from other's people post, and for the new "mandatory" (which I do not agree as stated above) UG-44(b), if your calculation fail, just tell your customer: increase flange rating with cost impact. This is the most simple fix instead of using Appendix 2.

I am expecting UG-44(b) to be removed from Div 1 and put into B31.3 in the future.

 

[KevinNZ]

Note. UG-44(b) can not be used on it's own to check or specify flange/nozzle loads. You also need to check the stress in the vessel and nozzle wall.

 

[TGS4]

UG-44(b) will not be removed from Division 1. In fact, it will likely be expanded with additional methods. And although the wording doesn't make it mandatory today, expect changes in the future that will make it mandatory.

However, a reference to it may be added to the various B31 codes.

KevinNZ's comment is well to note.

 

[r6155]

ASME VIII Div 1 UG-44 (b) “External loads (forces and bending moments) MAY be evaluated for flanged joints with welding neck flanges chosen in accordance with (a)(2),………………”
This mean that slip-on flange(say Class 150,no corrosion,etc.,etc) cannot be used with external loads?.

Regards

 

[SnTMan]

TGS4, I hope some provision is made for replacement equipment. It must be.

Regards,

Mike

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

 

[OnG_Engr]

Appendix 2 flanges for replacement equipment.

 

[jtseng123]

Please keep the following in mind:
Loads at nozzle to shell/head junction are completely different concept than nozzle loads at the face of flange.
Many companies have the spec of nozzle load table, which can be huge for the sake of safeguarding the "junction" with extra reinforcement. But applying these loads to "face of flange" is totally incorrect and unduly.

The face of flange can only take the load = (Flange pressure rating -MAWP). Period, and it must be verified by pipe stress engineer in each engineering company, not by vessel engineer. Pipe stress engineer must qualify it by adjust piping flexibility analysis using CAESAR II or other software.

By the same token, slip-on flange can take external loads just following the limit of (flange pressure rating -MAWP)

UG-44(b) shall be revised to avoid lots of issues. I currently have seen issues from vessel fabricator who is struggling to meet UG-44(b) and asking me what to do. I told them to ask their customer to provide the actual piping load at the face of flange, or simply raise the flange rating and back charge their customer of their customer insisting using the huge nozzle load at the shell/head junction to apply to face of flange.

 

[SnTMan]

OnG_Engr, what does the customer do about his mating flanges? They are presumably no good either.

To repeat: Can 'o worms...

Regards,

Mike

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

 

[r6155]

jtseng123, thank you
1) I know the difference.In example, vertical vessel: discharge nozzle in the bottom head, 90º elbow, horizontal pipe and flange near the skirt. This flange is the matter in UG-44 (b).

2) Different concept is in API 660. Please see:
Figure 4—Directions of Moments and Forces on Nozzles
Table 2—Nozzle Allowable Forces and Moments at the Nozzle Neck to Shell/Channel Interface

I Agree with you: UG-44(b) shall be revised to avoid lots of issues.

Regards

 

[marty007]

One issue that I'm seeing with UG-44(b) is paragraph UG-44(b)(2):

(2) The actual assembly bolt load (see Nonmandatory Appendix S) shall comply with ASME PCC-1, Nonmandatory O.​

In the same way that many B16.5 flanges fail an Appendix 2 analysis, I'm now finding that some ASME B16.5 CL150 RFWN flanges fail the PCC-1 anslysis! What is the path forward in this situation?

 

[OnG_Engr]

SnTMan - Is there a Code requirement for both flanges to be Appendix 2 to apply rigidity?