C
C.0.
26559
13
No. 7 Carteret St., 22 JUL 08
Westminster,
April 28th, 1908.
90
To the Crown Agents for the Colonies,
Regn, 254
Gentlemen,
(1)
In reply to your letter dated 3rd April 1908, I beg to state that, for many years past it has been my practice to specify, both for oast-, as well as wrought- iron pipes, the test-pressure, and not the working-
pressure.
In the (2)
I do so,
for the following reasons. case of cast-iron pipes, I have found that if a very high test-pressure is applied, and if the pipe is hammered, whilst under pressure, flaws may be caused, which do not make their appearance until after the pipes have been delivered and exposed to working-conditions.
(3) In the case of wrought-iron, or mild-steel pipes, the minimum thickness, which is consistent with sound manufacture; and as to durability, is so much in excess of that which would be required, merely to with- stand the maximum working-pressure, that it suffices to specify the test-pressure.
(4) In the present case, I specified the test - pressure, which, as usual I estimated, at the rate of one pound per square inch, for each foot of head of maximum working-pressure, this also allows for extra head due to friction when the pipe is encrusted. amounts to a coefficient of safety of 2.3. cases, this ratio has been found to be amply sufficient.
This
In all other
1