The fact that steam piping methods have not kept pace with the demands
of higher pressures and modern practice is evidenced by the increasing
number of accidents from the failure of pipes and fittings.
There has not been, for the rapid increase of pressure used, a
proportionate increase in strength of flanges, number and size of
bolts used, and more generous provision for expansion and contraction.
Valves and fittings also require greater attention in their design,
construction and manipulation.
It is well known that the presence of condensed water in pipes is a
source of danger, but little is known of what exactly goes on in the
pipe. We have the incompressible liquid, the expansive gas, and the
tube with a “dead head” or dead end as it is called, or where the end
of the pipe is closed. Seeing that the tube or pipe is capable of
withstanding all the pressure that the steam can give, it is difficult
to account for the tremendous repelling force, which is, undoubtedly,
brought into operation in explosions or ruptures of steam pipes
carrying what are now comparatively low pressures.
The cause of the bursting is undoubtedly _water hammer or water ram_,
which accompanies large, long steam pipes, filled with condensed water.
If steam be blown into a large inclined pipe full of water, it will
rise by difference of gravity to the top of the pipe, forming a bubble;
when condensation takes place, the water below the bubble will rush up
to fill the vacuum, _giving a blow directly against the side of the
pipe_. As the water still further recedes the bubble will get larger,
and move farther and farther up the pipe, the blow each time increasing
in intensity, for the reason that the steam has passed a larger mass
of water, which is forced forward by the incoming steam to fill the
vacuum. The maximum effect generally takes place at a “dead end.”
In fact, under certain conditions, a more forcible blow is struck
when the end of the pipe is open, as, for instance, when a pipe
crowned upward is filled with water, one end being open and the steam
introduced at the other. A bubble will in due time be formed at the top
of the crown, when the water will be forced in by atmospheric pressure
from one end and by steam pressure from the other, and the meeting of
the two columns frequently ruptures the pipe.
The remedy for this is simple, the pipes must be properly located so as
to drain themselves or be drained by rightly located drip cocks. The
drip should be the other side of the throttle valve, and if steam is
left on over night this valve should be left open enough to drain out
all the water.