Minimum reaonable value of out of roundness of formed shell

[BasakAbhishek]

Hello,

What is the reasonable valve of out of roundness [as defined by UG-80(a)(1)] that can be obtained after correction? UG-80 says "the difference between maximum and minimum inside diameters at any cross section shall not exceed 1% of the nominal diameter". What I would like to know is as per good manufacturing practice, what is the minimum value of the "difference between maximum and minimum inside diameters"? Also, how is tthe correction done?

In particular, I am interested in a shell of nominal ID of 1860 mm, 30 mm thickness, material: Inconel 600.
Thanks!
Abhishek

 

[saplanti]

The engineering practise is part of the manufacturing process. At least you have a given nominal internal diameter and wall thickness. The nominal diameter is 1860+30= 1890 mm.

Assume +/- 0.5% of the nominal diameter for max and min nominal diameter targets. This value is 9.45 mm.
the minimum nominal diameter will be 1890-9.45=1880.55 mm and,
the maximum nominal diameter will be 1890+9.45=1900.45 mm.

The minimum internal diameter will be 1880.55-30=1850.55 mm
The maximum internal diameter will be 1900.45-40=1870.45 mm.

But your target is to be able to meet the given internal diameter, and you will prepare a template for the rolling application and watching to maintain the internal diameter during the longitudinal welding process.
During the inspection you will only watch the min and max internal diameters to satisfy the code rule.

I would expect from you you know all these as a manufacture. This is the geometry only and core part of rolling process.

If you made a mistake it is difficult to repair. But you may have a chance of correction if the circumferance of internal surface is the exact development length of internal diameter. This length is 5443.36 mm. You can take the peace on the roller and roll untill you get dimensions within tolerances. Otherwise you have to cut the full longitudinal weld and make corrections if your process is allowed by the metallurgist.

 

[r6155]

First you need to define the neutral axis of curvature. Not always is in the middle of plate thickness.
4 rolls rolling machine also have a function of roundness correction and leveling.

Regards

 

[saplanti]

Please check the following for the neutral axis for rolling.

https://www.cmrp.com/blog/plate-rolling/calculating-the-developed-length-of-a-rolled-cylinder.html

 

[saplanti]

And this one.

https://www.cmrp.com/blog/plate-rolling/the-neutral-access-and-considerations-for-bending-plate.html

 

[r6155]

Yes. Always try with 4 rolls rolling machine.
Regards

 

Measurement of out of roundness with the given dimensions will be complicated by sag.

'Minimum' and 'reaonable' are words that can not be placed side by side in the design world. Somewhere there is a criterion, with no middle ground.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."