Nozzle Flange Load Calculation 4

[weeeds]

Is it common to also examine the stresses on the WN flange attached to the nozzle when calculating the ability of a nozzle to withstand specified nozzle loads?
Thank you

 

[vesselguy]

widla,
Your original question does not ask about "testing". When you say testing, I interprete it mean NDE or some mechanical testing. If so, my humble opinion for you is no, you don't do any testing when the B16.5 flange is evaluated for external loads.

But you are still wondering if it is normal to "also" check the stresses in the flange when checking nozzle stresses due to external piping loads, the answer is No. Having said the general answer, you need your own engineering judgement to deceide whether you need to do it or not depending on the design conditions you are looking at.

Good luck.

 

[TGS4]

vesselguy - you and I agree on the answer to widla's question. The flange is usually not the weak point in the system.

 

[weeeds]

Thanks guys.
My recent wording was not correct. I did not mean "testing" as in NDE, I meant evaluating using calculations, FEA, or something like that.

 

[unclesyd]

Something that bothers me in several recent threads is the problem with external loads on vessel nozzles and especially flanges. It has always been our policy to limits any extraneous loads on nozzles and flanges to sevral hundred pounds by telling the piping design people
to keep their damn loads off my vessel. We have always found this to be easily accomplished by using the inherent flexibility of a piping system. I personally have never seen where the initial loads cannot be mitigated by a careful study of the piping. If it takes more that a couple of 500 lb. chain falls during installation something is amiss.

As I've stated before we have systems that a highly cyclic service at 2000 psig @ 600F where we used Class 2500 flanges with spiral wound gaskets. The Class 2500 flanges are for gasket seating. Parts of this system is on a make and break cycle of two weeks. These flanges do not leak. This system has also proven that if the proper flange is used and made up properly they can be very forgiving. Sometime ago when the problem of flange leaks got on the front burner we had teams to attack the problem, which we didn't have. The jest of the story was that after reams and reams of nebulous numbers were rolled out for all the site piping systems the only meaningful results were that gasket seating ruled with the primary stress coming from thermal expansion. Take care of these two conditions using any method and you are pretty certain that you can maintain the integrity of the piping system.

Flanges on our site were like the flavor of the month on 3-4 year cycle.

The above mentioned piping was once converted to a system of lap joint flanges. We used Schedule 80 stub ends where we welded the edges of flange and used 4 bolt backup flanges. This was to eliminate the gasket. We also made the raised face 1" high on some Class 2500 flanges by cutting the flange face back and doing the same thing but again only using 4 bolts to handle the hydraulic end force. This concept evolved from an older process that operated operated at 6500 psig where all flanges were thread on 2" pipe or tube with the gasket being a modified Bridgman ring, self energizing. The flange was four bolt two inch thick piece.

I shouldn't tell this but if you have enough flange for the job you can profane all the rules with no trouble at all. On each of polymer process units we have a 2 piece bypass line around a process filter that consists of 8 ft of pipe with a Grayloc on one end and Class 2500 flange on the other. The Class 2500 flanges are normally made up with no problem, but in time the pipe spools shorten or get mismatch where the gap exceeds the spacing for one gasket to seat. The answer initiated by the mechanics was to put two or three spiral wound gaskets to act like a dutchman. I can't tell the maximum number that have been used. The system has never leaked.

Again if you got a properly designed flange strange and wondrous things can be accommodated. I've mentioned this before where we have a system, 24", that operates at 250 psig @ 1200F where the spiral wound gasket filler has to be mica. On two occasions graphite filled gaskets have been used with no problem even though the graphite was oxidized almost instantly by the process. The spirals alone held.