Weld prep design for SS pipe of different thickness.. and..

[Ralph2]

I have been asked to design a weld prep for a 13" OD pipe with a wall thickness of 5/8 316 SS to a tapered transition piece that has a wall thickness of 3/4", is 36" long and tapers to ~11".
So, no problem with a traditional "vee" weld prep, taper the inside to suit the larger ID. But.. with SS does the gap change? fudge up or down??

BUT.. the biggest challenge.. is to keep the cone end aligned with the main pipe. This will be the conveyor part of a centrifuge.. and the specs call for a maximum runout of +/- 0.005. ( I know.. lots of luck with that).

My best chance to maintain alignment would be to have a weld prep with no gap.. but I need a 100% weld.

Anyone with any thoughts .. ideas on how to at least try to achieve the tolerance.. with 316 SS

Thank you for your time.........

 

[DekDee]

Ralph,
Use strips of 316 plate the equivalent thickness of your required root gap.
Tack them in to the prep as you would for bridge tacks.
Put in eight of these equally spaced around the pipe.
Weld the areas in between the spacers (alternating to the opposite side of pipe each time) giving ample time for pipe to cool down between runs.
Remove spacers and weld remaining sections.
Don't weld bottom to top if it is in the 5G position as most shrinkage will occur at the top.
Weld in quadrants (6 o'clock to 9 o'clock, 3 to 12, 6 to 3 then 9 to 12)
Hope that helps and good luck,
Cheers,
DD

 

[racookpe1978]

You should be able to find a consumable insert of the right filler material for that diameter. A bit pricey for just one, but the comsumable insert will act as a backing strip for the welding from the outside, and shield better (not perfectly!) the interior surfaces if you cannot get a good back purge of an inert gas.

 

[Ralph2]

Thanks to both..
Spacers / shims are what I had in mind as well... but with SS I suspect the shrinkage will crush the spacers to some degree, be a bugger to remove and still cause my assembly to bend. Can't be helped.. but perhaps it will keep me in the ball park.

racookpe1978.. can you tell me more about the "consumable insert"? A link? Supplier??

 

[Tmoose]

I expect the pipe and transition will inherently have runout and even variations in wall thickness > 0.005". If this rotates with the centrifuge, and the intent of the runout spec is to provide an acceptable level of inherent balance, I think they are doomed. Maybe they are trying to limit the amount of balance corrections that will be required.

Is this a First Of A Kind product?

 

[Ralph2]

Thanks Tmoose
Yes.. I agree with your "I think they are doomed. Maybe they are trying to limit the amount of balance corrections that will be required.
".
I am not sure about this being a "First". Given the drawings I have seen so far this is several steps before a "first". At the moment (to me) this appears to be a "fools errand" kind of quote. I have been asked to sit in with the customers (engineers?) at a meeting soon where I may get to ask a number of.. "OK, how are you going to deal with..."

 

[racookpe1978]

http://www.imperialweldringcorp.com/consumable-inserts.html

Above is a link to the kind of insert I have used before: gives descriptions, material, ring sizes, etc as well. It's been a while since I purchased any though.

 

[Ralph2]

Thank you racookepe1978
Definitely something that would "help" with my alignment.. both angular and radial.