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...

 

[SnTMan]

OnG_Engr, I am talking about replacing a piece of equipment built in, say, 1962. The buyer needs a new pressure vessel. The buyer does not need to uprate every piping flange in the plant.

Doesn't mattter what Sec VIII, Div 1 says this year.

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

 

[OnG_Engr]

SnTMan,

I'm assuming your new equipment is fabricated to the 2019 Code. My interpretation of Appendix 2 is that only one flange has to meet the rigidity requirements. Design your Appendix 2 flanges to mate with the older flanges. You just need to beef up the side towards the vessel while leaving the mating side, bolt circle, etc. the same. Let's do a thought experiment: One normally only gets to use half the gasket width due to flange flexing. If both flanges were infinitely rigid, all the gasket width should be available. If one flange is infinitely rigid and the other "normal", then the gasket width available should be somewhere between 1.0 and 0.5 of the available material. By this logic, I think you will get a benefit from just having one flange being the extra rigid Appendix 2. I assume that if both flanges were required to be Appendix 2 for rigidity benefit, the Code would say as much as this would be an unusual application.

Thoughts?

 

[jtseng123]

I saw people are confused with B16.5/B16.47 standard flanges vs. Appendix 2 in this post.

Standard flanges are set to be used based on more than 50 years experience with the pressure-temp rating table as the sole guideline. People shall not use Appendix 2 or any other code or FEA to justify standard flanges. Use the standard flanges as is. Only if custom made flanges, then you will use Appendix 2, which is conservative, to design it.

There is no benefit to custom design flanges 60" and under. Simply raising flange rating on both nozzle and mating flange will save you a lot if external loading at the face of flange is too large. We did this way many times in large inlet nozzles that pipe stress engineer could not reduce the loading at the face of flange due to short pipe routing which does not provide sufficient flexibility.

 

[SnTMan]

OnG_Engr, the Code says nothing, requires nothing, of the connecting flanges. They are excluded from its scope.

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

 

[OnG_Engr]

jtseng123 - agree with not using Appendix 2 to justify B16.5 flanges. Disagree about cost savings, especially when it comes to B16.47 sizes. Also keep in mind that any valves that bolt to the flange have to have the higher rating.

 

[OnG_Engr]

SnTMan - Thanks for the confirmation!

 

[SnTMan]

Substitute slip-on flanges for weld necks. Problem solved.

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

 

[r6155]

Slip-on flanges shall not be used in any of the following conditions:
a) design pressure greater than 2100 kPa (ga) (300 psig);
b) design temperature greater than 400 °C (750 °F);
c) corrosion allowance greater than 3 mm (1/8 in.);
d) hydrogen, sour, or wet hydrogen sulfide service;
e) cyclic service.

Regards

 

[OnG_Engr]

I have been issued orders from above to just tell the Customers to anchor their piping for zero loads on our flanges. I tried...

 

[SnTMan]

r6155, I wasn't completely serious. But it illustrates the difficulties of the current rules.

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

 

[r6155]

SnTMan, You are serious 100%

Regards

 

[SnTMan]

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

 

[BJI]

I would be interested to know what other methods would be added, other than the most likely candidate, the ASME III NC-3658.3 method. I reckon a fair bit of conservatism could be removed from the UG-44(b) moment factor for the B16.5 CL150 flanges, and/or preferably have it variable to suit higher capacities in smaller bore flanges.

 

[BJI]

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?

How can you fail a PCC-1 Appendix O calculation, do you mean the maximum assembly bolt load is lower than expected?

 

[marty007]

How can you fail a PCC-1 Appendix O calculation, do you mean the maximum assembly bolt load is lower than expected?

B16.5 flanges have quite a large gasket area compared to many custom Appendix 2 flanges. I've run into a few where the gasket area is so large that there is insufficent bolting to achieve the target gasket stress, while staying within typical recommended bolt stress limits. We end up having to come up with torque values outside of the gasket suppliers recommendations...

 

[TGS4]

BJI - thank you for the reference to III NC-3658.3.

SnTMan - there seems to be an appetite for successful past service as a criteria. The challenge is demonstrating that to the inspector's satisfaction (and an understanding of the design margins inherent in past successful experience).

For those of you with specific issues about UG-44(b), please provide recommendations for modifications. I am in the process of proposing an update - this is your unique opportunity to have a direct say to Code modifications.

I agree that we didn't get things perfect this first time. But it was better than the no man's land that was the previous status quo.

Note that the values in the Table are out of bounds unless there is a published paper that provides a technical justification. The current values are based on PVP2013-97814. And that paper only investigated welding neck flanges - if someone does the work on slip-on flanges, then we'll add that to UG-44(b), too.

 

[SnTMan]

TGS4, re replacement equipment and successful experience: Is the owners determination that it is so not sufficient?

I.e., owner / buyer / whoever in inquiry / purchase / whatever documents states "UG-44(b) is not applicable". Or some such.

Further, the statement "The challenge is demonstrating that to the inspector's satisfaction (and an understanding of the design margins inherent in past successful experience)" seems to imply that the Inspector must be satisfied with other basic design issues. To include temperatures, pressures, corrosion allowances, process parameters, materials, to no end? Surely not.

Re UG-44(b), please retain the word "may".

Edit: Please don't interpret my remarks as criticism of the efforts you and the other committee members make. Not intended as such

Regards,

Mike


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

 

[OnG_Engr]

TGS4 - One solution I have been considering is to create an Appendix 2 flange designed to mate with a particular class that has an equivalent geometry to the next higher class for purposes of UG-44. Specifically, a thicker flange can have increased resistance to flexing and thereby maintain gasket seal integrity. Create a table with dimensions on how to beef up a flange to create this equivalency.

 

[SnTMan]

OnG_Engr, I am possibly missing something and I don't have access to Edition 2019, but, looking at CC2901: If a B16.5 flange (or B16.47 for that matter) of a given size and class does not meet Eqn 1) of the same, I don't see how a mating Apx 2 flange can be shown to meet it.

Are you saying the quantity PR can be shown to be greater than PD such that the Eqn 1) is met?
Are you saying since it is not a UG-44 flange, UG-44 need not be met?
Something else?

I have a couple other difficulties with this approach but put them aside for now.

Regards,

Mike

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

 

[OnG_Engr]

SnTMan - I think we have two issues:

(1) My understanding is that you believe both flanges must be the same to get a benefit to the sealing. I believe only one flange needs to have greater rigidity, stiffness, etc. to benefit as the useable gasket width will increase and ASME should have taken this into account. I'm not just playing "loophole-in-the-rules" games. This may need an Interpretation to resolve, though what's the point of calling out rigidity if you can't use it under most circumstances?
(2) A long time ago I used to use Roark formulas to calculate ring twist on the flanges of vertical turbine pumps. My thoughts are to use something like this to figure out how much thicker one would have to modify the design of a 600# flange (for example) to have the same reaction moment as a stock 900# one. Therefore, if a 900# B16.5/B16.47 flange would pass using the formula in UG-44(b), there should exist a beefier 600#-equivalent that would work for gasket sealing due to greater flange thickness.