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WATER CONDUCTORS AND ACCESSORIES 



It would seem advisable in proportioning the thickness of 

 penstocks to provide in addition to the thickness computed by the 

 above formula, an allowance for corrosion, that is, the addition 



FIG. 60. Ten Five-foot Riveted Steel Penstocks. 



of a constant term to the thickness, say inch or whatever is con- 

 sidered advisable under the conditions of installation. 



Another point which must be given very careful consideration 

 in connection with the calculation of pipe-line sizes and thicknesses 

 is their safety from collapsing, due to sudden drop in pressure. 

 The following formula gives the maximum difference between 

 the external and the internal pressures which a circular steel pipe 

 can withstand: 



p = 50,200,000 



(I) 1 



w 



Where 



p = pressure difference in pounds per square inch; 

 t thickness of plate in inches ; 

 d = diameter of pipe in inches. 



