Figure 12 shows a 4-inch- ID x 

 12-inch-long (90% water-filled) speci- 

 men assembly and the remains of a 

 similar (except air-filled) assembly after 

 failure by implosion. The violence of 

 the implosion of the air-filled specimen 

 is shown by the granular nature of the 

 remains of the glass pipe (the small 

 pile of white material seen between 

 the end closures). 



The 4- and 6-inch-diameter 

 pipes that were too long to fit into the 

 NCEL pressure vessels were assembled 

 with tie-rods (used between the end 

 plates) and were left completely filled 

 with air (no water inside). These pipes 

 were tested by taking them to sea and 

 lowering them into the ocean until 

 they reached implosion depth. The 

 violence of the implosion was suffi- 

 cient to be heard aboard ship by 

 means of a hydrophone hung in-the 

 water below the ship. Thus, the time 

 of the implosion was known, the wire 

 angle and the amount of wire necessary 

 to reach implosion depth was noted. 

 The depth of implosion was then 

 derived. This depth was then converted 

 to critical pressure. 

 The technique of mitigating equipment damage (from the violent 



implosion of void specimens) by almost completely filling the test specimen 



with water brought up the following questions; 



1 . Was sufficient void space being provided to compensate for the 

 volume reduction of the glass pipe— end closure system at high 

 pressures? 



2. Did this technique have any effect on the critical pressure of the 

 specimens tested? 



Figure 5. Simplified hold-down system 

 used in majority of short- 

 term critical pressure tests. 



