Figure 12-7.Tube corrugation resulting from oil on waterside.
Waterside Inspection of
Drums and Headers
Whenever a boiler is opened for cleaning and
overhaul, the internal surfaces of the drums and
headers should be carefully inspected for evidence
of cracking. Particular attention must be given to
steam drum manhole knuckles, knuckles at
corners of drum heads, corners of cross boxes and
headers, superheater header vent nozzles, and
handhole openings. Any defect found must be
recorded in the boiler water treatment log and in
the maintenance log. These defects should also be
reported to the maintenance office so that
appropriate repair action can be taken.
Boilers are tested hydrostatically for several
different purposes. In each case, it is important to
understand why a test is being made and to use
but NOT to exceedthe test pressure specified for
that particular purpose. In general, most
hydrostatic tests are made at one of three test
pressures: boiler design pressure, 125% of design
pressure, or 150% of design pressure. Other test
pressures may be authorized for certain purposes.
For example, a test pressure of 150 psi is required
for the hydrostatic test given before a boiler
undergoes chemical cleaning.
The hydrostatic test at design pressure is
required upon the completion of each general
overhaul, cleaning, or repair that affects the boiler
or its parts and at any other time when it is
considered necessary to test the boiler for leakage.
The purpose of the hydrostatic test at design
pressure is to prove the tightness of all valves,
gaskets, flanged joints, rolled joints, welded joints,
and boiler fittings.
The test at 125% of design pressure is
required after the renewal of pressure parts, after
chemical cleaning of the boiler, after minor welding
repairs to manhole and handhole seats, and after
repairs to tube sheets, such as the correction of
gouges and out-of-roundness. The renewal of
pressure parts includes all tube renewals, rolled
or welded, except downcomers and superheater
The test at 150% of design pressure is
required after welding repairs to headers and
drums, including tube sheet cracks and nozzle
repairs, after drain and vent nipple repairs, and
after renewal or rewelding of superheater support
tubes and downcomers. The hydrostatic test at
150% of design pressure is basically a test for
strength. This test may be (but is not necessarily)
required at the 5-year inspection and test.
Before making a hydrostatic test, rinse out the
boiler with freshwater. Using at least 50-psi
pressure, play the hose onto all surfaces of the
steam drum, the tubes, the nipples, and the
headers. Examine the boiler carefully for loose
scale, dirt, and other deposits. Be SURE that no
tools or other objects are left in the boiler. Remake
all joints, being sure that the gaskets and the
seating surfaces are clean. Replace the handhole
and manhole plates and close up the boiler.
Gag all safety valves. Boiler safety valves
must NEVER, under any circumstances, be lifted
by hydrostatic pressure. When gagging the safety
valves, do not set up on the gag too tightly or you
may bend the valve stems. As a rule, the gags
should be set up only handtight.
Close all connections on the boiler except to
the air vents, the pressure gauges, and the valves
of the line through which water is to be pumped to
the boiler. Be sure the steam-stop valves are
completely closed and that there will be no leakage
of water through them.
After all preparations have been made, use
the feed pump to fill the boiler completely. After all
air has been expelled from the boiler, close the air
vents and build up the hydrostatic pressure