Figure 39. A typical example of radial cracking (4-inch-IDx 6-inch-long 

 pipe with stainless steel 316 end-closure plates externally 

 pressurized to 20,000 psi). 



There are many analytical expressions for the calculation of critical 

 pressure in cylinders with or without stiffeners. Generally, the complex 

 analytical expressions are better than the simple expressions for predicting 

 the critical pressure. Thus, at first glance, it would appear that it is much 

 more desirable to use complex expressions than the simple ones since the 

 calculated critical pressures will be much closer to the experimental ones. 

 Unfortunately this is true only so long as detailed measurements and spec- 

 ifications exist for the given test specimen, as when it is an item custom-made 

 to very rigid dimensional and material specifications. 



For mass-produced glass pipes with conical flanges detailed specifica- 

 tions to close tolerances are not available because in the mass-production 

 fabrication process large variations in wall thickness, roundness, and quality 

 of glass welds exist. Because of the discrepancy that exists between the 

 nominal and actual dimensions of the pipes, calculated values must differ 

 considerably from experimental values even if the analytical expression 

 used in the calculations is the correct one. Because of this discrepancy, 

 little can be gained by going to elaborate analytical expressions when only 

 the nominal pipe dimensions supplied by the manufacturer are used in the 

 calculations. 



38 



