抄録
Recently, not a few rupture accidents of distribution pipes of water works have occurred at some cities in our country. The pipes ruptured were of high grade cast iron and had been considered to be safe from rupture, because their construction was not very old as we might expect such accidents.
To clarify the cause of the accidents from the view point of the strength of pipe, some static and fatigue tests were made, to which were put rectangular test pieces taken out from bodies of various pipes, that is, the pieces from ruptured pipes and unused pipes manufactured in different years.
Along with those tests, determination of chemical compositions and comparison of microstructures of cast iron were made.
Some of the test results obtained are as follows:
(1) The microstructure of cast iron manufactured in 1940, 1952 and 1954 were gray cast iron. According to the classification of ASTM, all the pipes belong to the type A of graphite flake type chart, and the pipes manufactured in 1940 and 1952 belong to the size 4 of graphite flake size chart, and the pipes made in 1954 belongs to the size 5.
(2) Comparing the fatigue strength of test pieces of the pipes of the same year with each other, the damaged pipes showed a very low strength in comparison to that of the series 2 taken out from unused pipes. The same tendency was shown about the static strength of test pieces.
(3) The test pieces, series 6, were taken from the ductile pipe, and their static and fatigue strengths were higher than the others.
(4) In forming the test pieces, each of which has a rectangular section, the cast skin of the pipes was removed. These treatments must have produced conditions considerably different from the actual state of the pipes, so that the strengths obtained from the tests showed somewhat lower values.
