The hydraulic test is a very convenient method of testing _the
tightness of the work in a new boiler_, in conjunction with inspection
to a greater or lesser degree, in the passing of new work. As a
detector of leakages it has no rival, and its application enables
faulty caulking to be made good before the boiler has left the works,
and before a leak has time to enter on its insidious career of
corrosion. The extent to which it enables the soundness and quality of
the work to be ascertained is another matter, and depends on several
conditions. It will be evident that if the test be applied with this
object to a new boiler, the pressure should range to some point in
excess of the working load if such a test is to be of any practical
value.
What the excess should be so as to remain within safe limits cannot be
stated without regard being paid to the factor of safety adopted in the
structure.
In addition to the advantage which the hydraulic test affords as a
means of proving the tightness of the riveted seams and work generally,
it is also of frequent assistance in determining the sufficiency of
the staying of flat surfaces, especially when of indeterminate shape,
or when the stresses thrown upon them by the peculiar construction of
the boiler are of uncertain magnitude. For the hydraulic test, however,
to be of any real value in the special cases to which we refer, it is
essential that it should be conducted by an expert, and the application
of the pressure accompanied by careful gaugings, so as to enable the
amount of bulging and permanent set to be ascertained. Without such
readings the application of the test in such cases is worthless, and
may be delusive. Indeed, the careful gauging of a boiler as a record
of its behavior should be a condition of every test, and is a duty
requiring for its adequate performance a skilled inspector.
The duty of inspecting a new boiler or witnessing the hydraulic test
properly belongs to one of the regular inspecting companies, who have
men in their employ specially trained for the performance of such work.
The advantage accruing from such a course is well worth the fee charged
for the service, and secures a searching inspection of the workmanship,
which frequently brings to light defects and oversights that a mere
pumping-up of the boiler would never reveal. Such a proceeding in fact,
can only prove that the boiler is water-tight, and a boiler may be
tight under test although the workmanship is of the poorest character.
Besides, it is well to bear in mind that the tightness of a boiler
under test is no guarantee of its tightness after it is got to work.
In a word, as far as new boilers are concerned, the application of
hydraulic pressure unaccompanied by careful inspection and gaugings may
be almost worthless, while with these additions it may be extremely
valuable, especially in the case of boilers of peculiar shape, and is a
precaution that should not be neglected.