122 



Bulletin 86 



made by running the pressure up quickly ; the last test and all the 

 tests at Tucson were preceded by a 15-minute seepage test. 



These results demonstrate that consideration should be given to 

 the condition of the pipe specimens and to the technique of testing. 

 Specifications do not mention either of these matters, but merely 

 fix a minimum pressure, usually 33 pounds, which the pipe must 

 stand. 



Four of the 12-inch pipe, two of which could not be broken in 

 the tests of 1917, were tested in June, 1918. The results are given 

 in Tabic X. All of these pipes were machine-made. During this 



TABLE X. TESTS OF FOUR 12-INCH MCCRACKEN PIPE UNDER VARYING 

 CONDITIONS OF SATURATION 



long period the four pipes had stood in the open air at the City 

 Water Works. Two of the four pipes were tested dry ; the others 

 were immersed in water, one for IjA hours, the other for 

 51 hours. The two dry pipes failed ; the wet ones could not be 

 broken. One and a half hours, in the case of No. 3, was long enough 

 to expand the pipe and stabilize the even distribution of stresses in 

 the pipe wall. In the case of No. 1, tested dry, the pipe was weak- 

 ened by holding water 31 minutes. During 10 minutes of this time 

 the pressure was kept at 10 pounds and twice the full city pressure 

 of 38 pounds was turned on. Finally the pipe broke at 33 pounds, 

 although in March, 1917, before the pipe had become dry, it had 

 withstood 47 pounds for 19 minutes. Pipe No. 4, also tested dry, 

 failed a quarter of a minute after the pressure reached 10 pounds, 

 although it had withstood 50 pounds pressure in March, 1917. 

 These tests tend to confirm the conclusions reached above. 



