Formed Heads | Dished Heads | Types of Head | Head Types: ASME Section VIII Div. 1 @ Whizz Engineers 

Circumference tolerance is not given in ASME Section VIII, please refer client specifications for circumference tolerance. Please watch the Dish Head inspection video: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-KSKEPA_ffhY.html

Vessel pressure bottom head formed plate name

I imagine at larger diameters (like the example shown) the amount of deformation needed to stamp/draw a hemispherical head from a single plate would either exceed the elongation-to-break of most materials, and even if it didn't just think of how large a press would have to be to both be powerful enough and have a deep enough stroke in order to perform the stamping. It likely just becomes cheaper and easier to do it in sections.

The limit of sheet metals width is the standard capacity width of the rolling mill. Anything requiring a wider sheet than standard is custom made or welded from the smaller sheet width.