Flat End Closure 



Closure Shapes 



End closures may be flat 

 or hemispherical (Figure A-9). Flat 

 end closures are more economical 

 to fabricate than the spherical 

 closures. However, because of the 

 severe bending moments that are 

 generated in flat closures by hydro- 

 static pressure when they are 

 restrained by threaded, shear-block, 

 or tie-rod restraints, flat closures 

 are limited to diameters of less than 

 3 feet in the pressure range above 

 5,000 psi. For higher pressures 

 and larger diameters, they become 

 rapidly unwieldly and uneconomical, 

 as forging thicknesses in excess of 

 several feet become necessary to 

 withstand the high bending moments. 

 The hemispherical end closures require much less steel than the flat 

 closures because of more favorable stress distribution in them, but the saving 

 in steel is offset here by the cost of forging and machining an intricate shape. 

 There are indications, however, that a technique for fabricating layered hemi- 

 spherical end closures may be developed that instead of expensive forgings 

 utilizes formed plate segments welded into a continuous structure. Because 

 of this new development, the current pressure and diameter limitation on 

 hemispherical end closures may be eliminated. 



Large, flat end closures are feasible for high internal hydrostatic pressures 

 only if a continuous-yoke end-closure restraint system is used on the vessel. In 

 such a case, a bearing block under the continuous yoke at the end of the vessel 

 restrains the flat closure from flexing, and only a nominal thickness is required 

 for the closure to retain the necessary seals around its circumference. 



Conclusion. It appears that the hemispherical end closures are more 

 desirable for large diameters and internal pressures than flat ones unless the 

 continuous-yoke end-closure restraint is used on the vessel. 



Hemispherical End Closure 



Figure A-9. Typical end closures. 



57 



