Apply water pressure of 1 1/2 times the
maximum allowable working pressure. To
avoid rapid shock and strain, bring this pressure
up in 10 equal increments, inspecting for leaks
and deformities at each increase.
Inspect tube ends, boiler seams, pressure
fittings, and connections. Make the corrections
and repairs wherever possible. In case of
unusual conditions, DISCONTINUE the test
IMMEDIATELY and NOTIFY YOUR
SENIOR PETTY OFFICER. Do NOT exceed
the test pressure. NEVER apply more than 10
pounds of pressure above the maximum
working pressure on a low-pressure boiler.
Consult the ASME code for testing procedures
for other than welded steel boilers.
Secure pressurizing connections at the required
test pressure. Continually inspect the boiler
tubes, seams, fittings, and connections. If the
boiler and fittings are tight, the pressure should
NOT drop more than 1.5 percent in 4 hours. If
loss of pressure is over 1.5 percent, find the
leak(s) and make the repairs.
Following all hydrostatic testing, steam pressure is
raised to lift safety valves and to determine the fitness
of the boiler for use.
Most cases of major boiler damage is caused by
what operating condition?
What could happen if "loose packing" is used on
a gauge glass?
What are the four reasons for using blowoff or
What is the purpose of a hydrostatic test on a
Learning Objective: Recognize and understand
methods for renewing, repairing, and cleaning boiler
tubes and sheets.
For any boiler retubing job, it is absolutely
essential to use tubes that conform in every way to the
tube requirements of the particular boiler. Boiler tubes
are NOT identical. They differ in such important
characteristics as composition of the metal, outside
diameter, wall thickness, length, and curvature.
Much of the required information on sizes,
thickness, and number of tubes per boiler is given in
the manufacturers technical manual. Some of the
information is under the heading of "Tube Data." More
detailed information is usually given on the drawings
included in the manual.
COMPOSITION OF BOILER TUBES
Generating tubes are usually made of low carbon
s t e e l . T h e y m a y b e e i t h e r s e a m l e s s o r
resistance-welded. Seamless tubes were once
definitely preferred for naval use. However, improved
methods of manufacturing the welded tubes have led to
an increased use of welded tubes in naval boilers.
Repair ships, tenders, and other naval activities that
use, handle, or issue plain carbon steel tubes have been
instructed to make no distinction between the seamless
and the welded tubes, but to stock, issue, and install
them interchangeably without regard to the method of
Superheater tubes usually are not made of plain
low carbon steel. On boilers where the superheated
steam temperature reaches 850°F or higher, the
superheater tubes may be made of carbon-
molybdenum steel, chromium-molybdenum steel, or
an 18-8 chromium-nickel (stainless) steel.
To find detailed information on the composition of
the metals used for generating tubes and superheater
tubes in any particular boiler, check the manufacturers
technical manual. The information may be given on the
drawings, or it may be included in the text.
Once you have found information on the
composition of the metals used for boiler tubes, your
next problem is to understand it. Do you know what it
means when you see "mild steel" on a blueprint? Can
you identify metals by their chemical symbols? Do you
know what an "alloy steel" is, or anything about the
different kinds of alloy steels? Do you know anything
about the various systems of classifying steels? Do you
know why different steels are used for different kinds
of tubes? Answers to these questions are necessary
before you can make much sense out of the information
you are likely to find on blueprints on the composition
of boiler tubes.
Although we all have a general idea of what we
mean by the word metal it is not easy to give a simple,
accurate definition. Chemical elements are metals if
they are lustrous, hard, good conductors of heat and
electrcity, malleable, ductile, and heavy. In general,
these properties of hardness, conductivity,