Minimum required thickness for pressure vessels

[Saver2008]

Hi!!!!

I want to know where exactly I can find the minimum required thickness that we can have when we fabricate a vessel, after process like rolled or bending. Or it come in ASTM???
This is for all kind of vessels, cilindrical and so on. And also for eliptical heads, torispherical and so on.

Thank you so much.

 

[Saver2008]

Hi again.!!!

I want to add something, i know that thickness firstable, you calculate it, for example we suppose for x process, we have 1/2". But when I rolled or bend it or do other fabrication process, due to stresses and so on, material will compress or other thing. And for example for the initial thickness 1/2", it down to 0.450" for example, what is the minimum thickness or limits of thickness after process.

Thank you so much.

 

[metengr]

Saver2008;
You need to figure this out on your own using your own shop equipment. Get some sample plate sections and form them and use your own results to decide on pre-forming thickness requirements.

 

[SnTMan]

Saver2008, ASME Code generally deals with minimum thicknesses and forming and corrosion allowances are added to it.

For parts you are not fabricating, the vendor should be able to supply the forming allowances, or you can order to "MIN" thickness, and let the vendor add the allowance.

Industry standards, such as TEMA and HEI will also specify a minimum (actually a minimum NOMINAL) thickness based on diameter.

Forming allowances are not generally necessary for rolling, but will be for forming heads, bending u-tubes, etc.

Regards,

Mike

 

[Saver2008]

Thank you so much everybody!!!!

SnTMan, I,m agreed with you, but for example, I´m agreed with you with vendors supply min allowance or mines. But for example, in the fabrication drawing, I already know by calculation that for X process my Y equipment will require minimum 1/2" thickness. So for corrosion I will give 1/8" so it adds 0.625". Now if my process of bending and rolling I have this for example:
1/2" then after Z process, I have 0.375", so the difference is 1/8" so after my calculation thickness results as 1/2", I add 1/8" for corrosion (if applies) and for Process. so total thickness is 0.75". -So my plate will be of 0.75 minimum-. and in the drawing must be this thicness (I mean total) or by calculation???
Please correct me.

Thank you all of you.

 

[gr2vessels]

Saver,
First you calculate the minimum thickness of the pressure bearing component (shell, heads, etc..), taking in consideration other structural strength requirements. Then you add to this the corrosion allowance specified by the project requirements. That is the minimum thickness you have to fabricate the vessel.
The various scenarios you mention are your fabrication additional allowances you have to add in the top of the minimum thickness calculated. You have to buy the plate with additional thickness sufficient to allow for fabrication losses of thickness, in order to make sure that the final thickness is no less than the calculated minimum thickness. For the parts you are not fabricating (like dished ends), you have to specify the minimum thickness after forming and the dished end fabricator will certify that minimum thickness you asked for has been achieved.
This final thickness, which includes all the allowances mentioned above is the thickness on the fabrication drawing, rounded up to the nearest standard thickness of the plate (since you cannot buy 0.971" plate, you have to buy the 1" plate and that 1" thickness is noted on your fabrication drawing).
Hope this helps,
gr2vessels

 

[Saver2008]

Hi gr2vessels!!!

Thank you so much with your support. So I according to this, for your example, my thickness in the drawing must be 1". And for example, for giving fabrication allowance, Do I write what gave me in my rolling or x process experience (like bending take off 1/8")so for example the noted dimesion with allowance will be 1" +0"-0.125"?????

Please correct me.

Thank you so much.

 

[gr2vessels]

Saver,
It is a bit more complicated than this, you need to learn about fabrication tolerances. You also need to learn about grafic representation and tolerances notation on the drawings.
On the fabrication drawing for a plate rolled in your workshop into a barrel you don't write the thinning allowance, because you have already accounted for in your calculations and it is already included in the plate selected. You only mention the relevant tolerances for inside or outside diameter, length, etc...Look up for the start in the TEMA standard for allowable fabrication tolerances of pressure equipment.
Cheers,
gr2vessels

 

[GenB]

I disagree alittle,
if you in a tight position of t you are in trouble, why
you are suppose to comply with the tol required and allowed by Code, if the std thinning is caddedm or deducted depending on the math you are using, you need to take a thickness meassurement and be sure you are not under the spec. is not a problem.
in your case you would take a t check after rolling and if within the 1/8th tol you are okay. rolling will not take hat much.
on formed hds 1-the fabricator gves the thinnest part meassurements per experience,
as a QC your job is to check the t of the materials specially at the thinned part.
genb
other than that
if you ahve plenty of metal