Reduction of thickness of a cylinder formed from plate

[ElCidCampeador]

Hello,

I want to know the reduction of thickness of a cylinder formed from plate (low carbon steel): is there a way (or formula)?
I have a plate which shall respect a M.A.F. thickness after being rolled...Is there a way to demonstrate it (before working, without measuring it after)? ASME VIII Div.1 Ed.'19 Table UG-79-1 suggests a formula for forming strain calculation, but now? Could it be useful for my calculation?

Thank you

 

[SnTMan]

ElCidCampeador, if you are using a vendor to roll plate, you could / should confirm with them, but I have never encountered a situation where rolling is considered to decrease the plate thickness.

Regards,

Mike

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

 

[ElCidCampeador]

ElCidCampeador, if you are using a vendor to roll plate, you could / should confirm with them, but I have never encountered a situation where rolling is considered to decrease the plate thickness.

If ratio D/t of cylinder is very low, forming strain could increase. Moreover, if minimum thickness from calculation is really close to nominal thickness of plate (just a matter of 0.1mm)...well, I think that in this (strange) particular case I would prefer to check in theory. I know that the last word belongs to who rolls the plate and his experience...but after all, to trust is good, not to trust is better.
Any ideas?

 

[SnTMan]

Not sure forming strain equates to reduction in thickness. Any theoretical basis other than perhaps Poisson ratio? More theory than I posses is needed....

Edit: 0.1mm? Really?

Edit 2: A couple of sheets of paper? Really?

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

 

[r6155]

ElCidCampeador
Can you tell us diameter and thickness of plate?

Regards

 

[ElCidCampeador]

Can you tell us diameter and thickness of plate?

O.D. 914mm
Plate thk=24mm
Min.thk from calcs=23,9mm

Plates that I usually purchase have tolerances acc. to EN 10029 Cl.B, which means -0,3 of undertolerance.
So in the worst case, there is a point with real thickness=23,7mm

According to ASME VIII Div.1 UG-16, if the difference between the real plate thickness and design thickness is less than the smaller of 0.01 in. (0.3 mm) or 6% of the design thickness, well I'm ok.

In my case the smaller between the 2 values is 0,3mm, so: 23,9mm-23,7mm<0,3mm? Yes.

BUT: what about all manifacturing operation AFTER, like plate rolling? In my case ratio D/t is not so bad, but the fact is that design thickness is so close to the real one...it could be a risk rolling a plate without consider any reduction of thickness (whether theoretical possible). What's your opinion?

 

[SnTMan]

I know nothing about the metric market, but can you not go up 1 mm? Can you not buy 1" (25.4 mm) pl?

In addition, having so little (none) excess thickness will penalize opening reinforcement.

I personally wouldn't cut that close...

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

 

[ElCidCampeador]

I know nothing about the metric market, but can you not go up 1 mm? Can you not buy 1" (25.4 mm) pl?

Suppliers usually sell plate with thickness like 10 or 11 or 12mm etc...but over a not definied thickness only even values are available or multiple of 5mm.

In my case I could try to find 25mm, assuming this thickness exists and it's available in a short time.
26mm I think it's easier to find, but the delta thickness/weight/dimension would become considerable.

I'm trying to find a way to use 24mm, supported by a sort of theoretical analysis...

 

[r6155]

For plate 24 mm you can state in purchase order "minimum thickness 23,9 mm", or "no undertolerance is allowed"

Regards

 

[ElCidCampeador]

For plate 24 mm you can state in purchase order "minimum thickness 23,9 mm", or "no undertolerance is allowed"

Yes, I know that this could be enough...but I just want to sleep peacefully.

 

[SnTMan]

...but I just want to sleep peacefully.

A little extra steel is cheap insurance

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

 

[ElCidCampeador]

2 Problems:

-No money for extra steel
-My client is hard of hearing

and your goose is cooked and served :/

 

[SnTMan]

Well, best of luck then...

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

 

[r6155]

No problem with plate 24 mm

Interpretation Number : VIII-1-04-92
Question(s) and Reply(ies):
Question: A pressure vessel that has no specified corrosion
allowance is made of plate that is ordered to a thickness equal to
the required design thickness. If the actual plate thickness received
is less than the required design thickness, but is within the
allowable undertolerance as given in UG-16(c), may the plate be
used in accordance with the rules of Section VIII, Division 1?
Reply: Yes

You can also see other interpretations of UG-16 (c)

Regards

 

[ElCidCampeador]

No problem with plate 24 mm

Interpretation Number : VIII-1-04-92

Thank you, I didn't know this interpretation and I find it very useful.

But my problem is more personal than a mere check acc. to ASME code, I mean it's working on thin ice...I would hope to find something stronger from a theoretically point of view than simply being in accordance with ASME.

 

[SnTMan]

My opinion: the cited interpretation merely confirms the language of UG-16(c). Perhaps not especially useful here.

My further opinion: ElCidCampeador, you are going to have to assure yourself that the completed as-fabricated sections meet the minimum design thickness. Perhaps a post-fab thickness survey if no computational or other method is available.

No money for extra steel, but money for a thickness survey?

Again, best of luck.

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

 

[ElCidCampeador]

No money for extra steel, but money for a thickness survey?

Well, actually no money for survey too I don't want to reach that phase of construnction without any ideas...

 

[r6155]

Try with equation in Appendix 1 1-2 (a) (1)

Regards

 

[DriveMeNuts]

Well, the definition of t in the code is the minimum after forming thickness.
For thin walled vessels the material remains in the elastic range during forming, therefore while the inside half is compessed and bulges inward increasing the thickness, the outside half is stretched decreasing the thickness. The final result is a shell with no change in thickness.

With thicker shells where plastic flow occurs, there will be at least some plastic hinge action going on. The inside surface will only compressively plastically flow for so much, while the out side surface can plastially flow indefintely, causing material to stratch and thickness to disapear. I think the only way to find out is with an Elastic Plastic Analysis. Also, Manfacturers will keep records of experience of rolling thick plates.

 

[SnTMan]

Try with equation in Appendix 1 1-2 (a) (1)

After confirming applicability. r6155, did you perhaps mean Appendix 1 1-1 (a) (1)?

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