Fabrication of a tubular cone transition piece 2

[Angre]

Hi,
I have a query regarding fabrication of Cone transition piece.
the cone transitions from 2000 mm to 1200 mm.the cone height is 3600 mm
As per contract, only a single longitudnal seam is allowed.
The fabricator cant roll such a long section, so he is proposing to roll the section in two to parts and weld, resulting in two longitudnal welds.
The client does not agree to such a proposal. Other possibility is to roll two cones of height 3600/2 = 1800 m, weld two longitudnal welds and finally connect with
one girth weld.
The attached picture give an idea of the situation.

 

[racookpe1978]

Seems like both his methods are trying to keep the two ends perpendicular as he rolls it.

IF (big IF there!) your sketch is even slightly to scale, I'd roll it as single piece but with the ends rolled into the two different diameters to make the cone. The seam will slightly twist from one end to the other, and the two ends will be skewed. Then, lay out the two end diameters and cut them square.

Try it with a piece of cardboard to scale.

 

[SnTMan]

Angre, well, your fabricator can only do what he can do. You've got to either seek a deviation from the client or find another fabricator.

You don't give any idea of the class of work involved, but in heat exchanger work I have never seen a one-piece cone, concentric or not. They have always been made of two (or more) pieces. They are not rolled, but formed by multiple "hits" on a press brake.

Regards,

Mike

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

 

[BUGGAR]

They form monotube towers for electrical poles from one piece if you are looking for an alternate. And their multi-sided. Valmont may make them, and others.

 

[andriver]

On the other end, I have never seen a two piece cone, but I work in a major ship yard for offshore structures so we have the right equipment.

 

[moltenmetal]

The client either needs to be willing to pay for what they want, or they need to accept what people can do for a reasonable price.

If they can articulate what they're trying to accomplish by having only one longitudinal seam, perhaps you can find a compromise.

If the welds are done properly with the required interior and exterior surface finish and NDE, and the part when complete meets the dimensional tolerances, what other problem do they represent to the client?

I've seen cones made like your right-hand drawing more than once. When you have a long, steep-sided cone, you seldom have a choice in practical terms when you're only making one or two of them.

 

[SnTMan]

...you seldom have a choice in practical terms when you're only making one or two of them.

Bingo

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

 

[MintJulep]

See thread725-371319 where several fabricators with the possible capability are identified.

However in your case the limit may not be process capability, but the availability of plate in such a humongous size.

To roll that big a cone from a single plate requires a plate on the order of 6500 mm long and maybe 3000+mm wide (I'm too lazy to lay it out).

Plate that size isn't sitting in the stock room waiting for the order to come along.

 

[Angre]

Hi all,
Thanks for so many comments, siggestions and observations.
I specifically want to know about the following.
With the 1 girth weld ,2 staggered longitudnal weld, will there be any potential issue ?
Like uneven contact along the girth resulting in weld of bad quality.
The Cone will support about 800 MT of load hence it is very important that weld quality be good.
Rgds
Angre

 

[SnTMan]

Angre, should not be any problems, given careful fit-up and proper welding. You might in-process inspect, if you wish.

Regards,

Mike

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

 

[Tmoose]

Is the thickness of the material mentioned?
Is the cone asymmetrical as sketched?
Is the load applied symmetrically to the small end (or if asymmetrical, centered over the large end)?

 

[tbuelna]

The properties in the weld joint will depend on the materials/process used to produce it. A very high quality weld can be produced using the proper materials, weld technique, heat treatment, and post weld processing.

 

[RolMec]

Hello Angre,

to get it straight: the contract requires the single seam design, the contracted fabricator however isn't able to mfgr. as per spec?!
--> ?Change of fabricator, as proposed elsewhere

If such requirement (single seam) is tied down contractually, there shall probably exist other very stringent requirements as well: tolerances on shape, mass limitations, weld execution?

from manuf. p. o. v.:
Due to the specificalities of rolling conical plate sections, the multipiece + welding design will show edge offset, for the long. as well as for the trans. welds. There might be specific standards for the intended application not allowing this or at least limiting its extent. If the finished part is subject to in situ weld examinations, the longer welds shall not be appreciated.
At an assumed 7/8" plate thickness the whole piece would weigh around 3.2 metric tons, so care is needed when handling semifinished parts to hve them keep their shape.

I'd propose you very carefully check the base specs and standards and keep the client closely involved.

How did you proceed?
Regards
R.

 

[tbuelna]

Angre,

Since the construction of this component was fairly well defined in the purchase contract, if you value your relationship with this customer it would seem to be a good idea to do whatever is necessary to deliver a product that conforms to the contract. Even if it means finding another subcontractor to fabricate the cone. I have experienced similar situations where a vendor requests design changes after accepting a PO because they did not bother to do a thorough job with their bid. I usually find it rather aggravating.

There are steel fabricators that can roll the cone you describe.

 

[SnTMan]

tbuelna, interesting, thanks for the link

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