Hemispherical head ASME Code Section VIII, Division 1

Just as for cylinders the ASME Code provides four different formulas for the design calculation of hemispherical heads. In order to determine the joint efficiency factor E the requirements listed in UW-3(a) referring to the joint category have to be accounted for. According to UW-3(a) the attachment weld of a hemispherical head to a cylinder is always classified as a Category A weld subject to circumferential stress. Since the hemispherical head therefore includes a Category A joint at all times, the ASME Code never considers it as a seamless, but always as a welded part. This also applies to hemispherical heads manufactured from seamless plates. Thus the requirements of UW-12(d) for seamless vessel sections must not be used. Due to that reason the joint efficiency factor of hemispherical heads, although without additional welds, shall be determined using paragraphs UW-12(a), (b) or (c) depending on the design and volumetric examination of the attachment weld.

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