Figure 35. Component parts for a 4-inch-ID prototype glass instrument 

 liousing for cyclical service to a depth of 1,000 feet. 



Failure by implosion produced a loud, sharp report clearly audible 

 up to 50 feet from the pressure vessel. High-pitched "cracking" noises were 

 generally heard prior to implosion. As implosion pressure approached, these 

 noises increased in amplitude and became clearly audible to personnel behind 

 a barricade several feet away from the pressure vessel. As the testing program 

 progressed, it became apparent that the inception of the cracking sounds was 

 not being reliably observed due to its initial low amplitude and ambient 

 noise. In order to observe this phenomena and positively determine when it 

 started, a contact microphone and an audioampiifier were procured and the 

 microphone securely attached to the outside of the pressure vessel. Using 

 this technique, it was noted that the first "cracking" frequently took place 

 at relatively low pressures. However, it should be noted that in some cases, 

 even though cracking noises were observed, there was no visible damage to 

 the glass tubes. This cracking noise in many cases may be generated by the 

 glass bearing surfaces dragging and "chattering" on the end closure as the 

 end of the pipe decreased in diameter in response to the external hydrostatic 

 pressure. 



The actual cracks observed in specimens appear to be of three 

 general types. First the cracking and subsequent spalling of very thin shards 

 in the area where the inside rim of the pipe contacts the end plate (Figure 37). 

 Second are the concentric shear cracks propagating from the pipe surface in 

 contact with the end closure (Figure 38). These cracks, in most cases, result 

 in the cracking off of the portion of the pipe flange which is greater in outside 

 diameter than the main section of the pipe, and thus unsupported. They 

 appear to be a result of a combination of the shearing of the glass pipe flange 



35 



