when marking on the plate, fitter will add 1 thickness to ID shell when calculate the lenght of the rolling plate (circumference of shell)? anyone can explain the theory behind?

why circumference = pi x (ID + t)?
why not circumference = pi x ID only?

thank you.

dear zola25,

acutally when fabricating we cannot get as we draw, as allowance the thickness is added in calculating the circumference. so, we can corrected if any mistakes done while rolling. its only a safety measure.

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Regards,

M.KASI

Isn't mean diameter for rolling (ID + t) ??

so the (ID + t) is for safety measurement or to calculate the circumference by using the mean diameter?

Dear Zola,

this subject is a responsibility of fabrication only.
Depending on the method of forming and the type of equipment, such a length is required in order have enough moment for the forming process and the capacity of the type of machine used.
As an Authorized Inspector you are suposed to verify by visual inspection in if necessary by measurement whether the result of the forming is complying with the requirements for roundness and misalignment.
I hope this information is of assistance to you.

H.Michael

zola,
When you roll plate the outside stretches and the inside contracts.
The mean diameter is your "neutral" point halfway between the ID and the OD.
If you wanted a 4 metre diameter tank (OD) and you multiplied 4 metres by pi for your length of plate you would not end up with 4 metres diameter (OD), it would be larger.
You need to multiply the mean diameter x pi.
4 metres minus thickness x pi will give you a plate length that when rolled will end up as 4 metres (OD).
4 metres plus thickness x pi will give you a plate length that when rolled will end up as 4 metres (ID).

Hope that helps,
Regards,
BB

Sorry, I have misinterpreted the question raised by Zola.
This is the right answer. Sorry for the confusion.

Horst Michael

i am new in this fabrication field.

thanks for your all valuable advice/answer.

zola,
I have edited my post above.
Not sure if I explained it well the first time,
Regards,
BB

Noted.
thank you

Dear All,
The Thickness is added because after addition of thickness you measure the length on the neutral axis of the plate & it is niether under compression or tension. thus accurate measurment is taken and no change takes place.
Instead for other fig. we calculate the N.A. and then add to id.

Ballbearing is correct and this is commonly called "Stretch Out"

I am newbie in this field,i hope i will become better in it...........

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There is no specific measurement you can come up with while the sides are growing. You can do just an estimate right by the instantaneous time that will help you get a measurement. But that in itself is no quick gauge as to how things are to fall through.

It can be a level of instant measurement or something that will only be used for safety.