securing a flared pipe end.

[doezer]

hi all...

im looking for solutions would appreciate any help i could get here, i dont have much experience in pipe flange design to be honest.
we're looking at the design of a pipe/flange connection here but unfortunately the butt weld stresses are just too high in the pipe wall to allow for a classic pipe/ butt weld/ neck flange design.

so im looking at alternatives.
a) socket weld : not suitable an option. the weld sees both hoop stress and additional shear stress and so the load on the weld is actually higher.

b) flare the tube end. this ensures load is reacted but only in one direction, the outward direction.
are there any common approaches to securing the flared end the other way. im not keen on any threaded design because this design sees vibrational loads,
so any threaded design must not loosen under fairly high vibrational loads

c) socket type weld but with interference fit of the pipe end, so that hoop stresses are not applied to the weld, it only works in shear.
this maybe could work and the weld stresses would be low, but the retention force of the interference fit would probably not be high enough.

d) forming a bead or groove on the pipe end, and then placing a split flange around it??

i posted something similar on this a few weeks ago. ive been on something else since so its still pretty much in the same place for now!

thanks
D

 

[LittleInch]

doezer,

If this is a continuation of the same post, then at the least you should provide a link to it so that you don't just get a repeat of the same information.

http://www.eng-tips.com/viewthread.cfm?qid=415861

you really need to provide some data and sketches / drawing of what you want otherwise you won't get any new information.

So to satart with please provide:

Material
Pressure
Temperature
Pipe size
Pipe wall thickness
Type of flange you need at the other end
Other issues ( vibration etc)

I think there was a lock of understanding previously as to why you can't butt weld this stuff - the phrase above "the butt weld stresses are just too high in the pipe wall to allow for a classic pipe/ butt weld/ neck flange design" doesn't make a lot of sense, at least to me, so could do with some explaination.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[doezer]

hi.

yes it is a continuation of the last one. sorry I should have added the link.
I did provide some sketches the last time. The link to the sketch is in that last thread.

Material is Al6061-T6.

Im not sure why the statement "stresses are too high in the butt weld" is not clear? They are too high. The butt weld has a knockdown factor for strength
because we are welding Al6061-T6 here and after weld it loses the T6 properties and is not as strong, and so the weld is the weakest point.
We dont want to heat treat back to T6 properties because the part is too big then and also it will distort after heat treat, and so we would lose all accuracies.

i attach a link to a cross section for a non-welded joint which I think is along the lines of what could work for us.
assuming we can get face seal and o-rings which can work down to cryo temperatures.

https://www.google.com/search?q=gs-...hXI5IMKHaauDw0Q_AUIBygC#imgrc=Dn67X6sMjMmT5M:

Because this is cryo we may need to re-design so the internal o-ring is replaced by a sealing weld. but otherwise assuming all parts are Alum. then this non-welded design could work?!

sorry if it all seems badly presented. its not the intention

 

[rconner]

While I don't know exactly what you are trying to describe re alternatives, but a well-done butt weld is pretty "efficient" - maybe butt-welded, but with stronger material?

 

[doezer]

Hi

I think the crux of the problem is this reduction in weld strength for 6061-T6 when welded.
so thats why the butt weld strength is in-sufficient, and im looking to go to a non-welded joint arranegement if possible.
apologies if that wasnt clear in the posts..