scope:

WRC Bulletin 444 reports the results of 190 model tests and failures of tori spherical heads in service. Seventy-two of the heads failed by buckling of the knuckle and 17 of the heads were pressurized until the heads failed by bursting or by rupture of the crown. The test pressures were compared with the design pressures obtained from ASME Section VIII rules which are limited to heads with L/t 500, ASME Code Case rules which are limited to heads with L/t 500, the French Code CODAP rules which apply to heads with D/t ratios up to 1000, and the ECCS rules which apply to heads with D/t ratios up to 1250. The margins of safety were found to vary widely for all of the rules. A new set of rules has been developed for design of tori spherical heads under internal pressure. The rules are applicable to heads with L/t or D/t ratios up to 2500 and apply to all ASME Code materials. The rules are based on three criteria: failure of the knuckle by buckling, limiting the maximum compressive strain in the knuckle to prevent gross distortions, and failure of the crown by bursting. The proposed rules provide a more accurate prediction of the buckling pressure and a more consistent upper limit on the compressive stress in the knuckle than any of the other rules considered in this report