Tests 123 



The sweating through the walls of the hand-made pipe at 5 

 pounds pressure was quite strong, and with 10 pounds pressure the 

 percolation was rapid. Even at 2 pounds or less, the uneven char- 

 acter of the pipe was apparent, the less carefully tamped portions 

 becoming wet on the outer surface immediately. It has been noted 

 often in the field that a new pipe line is quite porous; but it has 

 been found that the pipe improves rapidly in this respect and soon 

 becomes impervious except perhaps at occasional spots where tamp- 

 ing was poorly done. Hand-made pipe is usually coated on the in- 

 side with a wash of neat cement, partly to make it watertight and 

 partly to increase its carrying capacity. 



The machine-made pipe was practically impervious at 15 pounds 

 pressure. The slight sweating on the top corrugation is believed to 

 have come through the joint under the gasket. The inner surface as 

 made by the packer-head is very dense. Where the pipe is laid in a 

 trench with rich mortar in the joints, even the slight sweating on the 

 corrugation at the groove end is impossible. In no other way is the 

 superiority of the machine-made pipe so pronounced as in the perco- 

 lation test. 



Some advocates of clay pipe for sewers are asking that the per- 

 colation test be discontinued. However, the American Society for 

 Testing ]\Iaterials, in standard specifications just adopted, has in- 

 cluded percolation tests at 5 and 15 pounds for both clay and cement 

 sewer pipe. The test can be made in connection with the internal 

 pressure test without additional apparatus, and undoubtedly it will 

 be used increasingly in the future. The specifications of the A. S. 

 T. M. should be amplified to cover the condition of the pipe. 



One advantage of the hydrostatic tests is that they test every 

 part of the pipe in detail. For instance, if the tongue end is made 

 with an insufficiency of mortar in the hopper, or if the wall on one 

 side is thin, or in spots the mortar was not well tamped, the pipe 

 will fail because the defective part fails. On the other hand, the 

 external pressure test is much less likely to reveal a local weakness. 

 Records of pipe tests have been noted in which the pipe stood 

 considerably over 100 pounds pressure with no seepage. These 

 tests have been made usually on 8-inch pipe, which has thicker walls 

 comparatively than the larger sizes commonly used in irrigation 

 pipe lines. 



The question of what pressure heads can be considered safe for 

 machine-made cement pipe lines is an important one. A consider- 

 able factor of safety must be used by designers to allow for occa- 

 sional defective pipe that may get past the inspector and for the 



