Appendix B 

 EXPERIMENTAL EVALUATION OF RADIAL END-CLOSURE SEALS 



BACKGROUND 



For successful operation each pressure vessel requires seals at joints 

 between removable pressure vessel connponents. Since seals at best are poten- 

 tial sources of leakage, a concentrated effort is generally made to minimize 

 their number. Such a minimum is represented by a single 0-ring in the upper 

 removable closure. No way has been found to eliminate it from a pressure 

 vessel because access to the interior is mandatory for the insertion of test 

 specimens. In the case of stacked-ring or segmented modular design, in which 

 both the upper and lower head closures are removable, the irreducible minimum 

 of seals is two 0-rings, one in the top and one in the bottom closure, sealing 

 the joint between the closures and the walls of the vessel. Naturally, more 

 than two 0-rings may be and generally are used even with such a design. The 

 additional 0-ring seals however, are only a convenient substitute for some 

 other type of seal, for example, threaded pipe fittings. 



EXPERIMENTAL DESIGN 



To evaluate some of the large variety of existing, or feasible joint seals 

 for high pressure vessels, a small pressure vessel was designed in which seals of 

 varying design could be tested between the closures and vessel body (Figures B-la 

 and B-lb). In order to simulate the problems that will be encountered in the 

 operation of the full-sized stacked-ring or segmented pressure vessel, the seal 

 test vessel was also designed with free-floating end closures. In this design, the 

 end closures were permitted some vertical motion when internal hydrostatic 

 pressure was applied. In the seal test vessel, the end closures were affixed to 

 the pressure vessel by means of tie rods, which extended only a known and 

 limited amount when the interior of the vessel was pressurized. Although this 

 vertical movement of the end closures was very small (on the order of a 1/32 

 of an inch at pressures of 10,000 psi), it was sufficient for the end closures to 

 be free floating. The fact that the end closure was free floating made it impos- 

 sible to utilize with it any of the seals associated with nonfloating end closures. 

 Such seals generally rely on the wedging action between the end closure and the 

 vessel body to squeeze the seal so that it forms a watertight barrier. With free- 

 floating closures, seals must be employed that do not lose their sealing action 

 because of the upward movement of the end closure under load. 



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