Drums and Headers
Make up the highest and lowest parts of
the water and steam containing elements
in the boiler
Steam Drums
Function to accumulate the steam generated in
the tubes and to provide a space for the
separation of moisture from the steam before the
steam leaves the boiler
Function to provide reservoir for the water
required for proper operation of the boiler
Function to receive and distribute to the
downcomers the feedwater required for the
generation of steam
Water Drums
Function to distribute water to the
generating tubes
Function to provide a receptacle for the
accumulation of scale and other solid
matter which may be present in or
precipitate from the boiler water
Drums
Components of the Drum



Wrapper Sheet (upper sheet of the steam
drum and lower sheet of the water drum)
Tube Sheet (lower sheet of the steam drum
and upper sheet of the water sheet)
Drum Heads (welded to the ends of the drum
and contains manhole covers for access to
the drum)
Drums
Steam Drum
Inside
Diameter
Shell Length
Thickness of
Tube Sheet
Thickness of
Wrapper
Sheet
54”
Water Drum
Inside
Diameter
32”
10’ 8”
Shell Length
10’ 6 1/4”
4 11/16”
Thickness of
Tube Sheet
2 13/16”
1 ½”
Thickness of
Wrapper
Sheet
1”
Drums
The boiler drums are constructed from a high
temperature steel alloy.
Most drums are formed of two sheets of alloy
steel which is rolled into a semi-circular shape.
The lower sheet of the steam drums and the
upper sheet of the water drums are called the
tube sheets.
These are rolled with an increase thickness to
provide extra strength where the holes are
drilled for the insertion of the generating tubes.
Drums
The other half of the drum is called the
wrapper sheet.
The ends of the drums (drum head) and
headers are formed by forging.
The drum head has a central manhole to
permit access for inspection, cleaning or
repair.
These access openings are closed in
while the boiler is in service by means of a
manhole.
Drums
The wrapper, tube and drum heads are joined
together by robotic electric arc welding.
Next the nozzles for the various fittings are
hand welded.
The drum is then given a radiographic (X-ray)
examination for welding defects.
The drum then treated in an annealing furnace
to relieve stresses incurred during the various
fabrication operations.
Drums
After the annealing process is completed,
a hydrostatic pressure test is made at one
and one half times the design pressure of
the boiler (MAWP – Mean Allowable
Working Pressure).
If a defect in a weld appears it must be
ground out and be rewelded.
The weld must then be X-rayed again,
heat treated and pressure tested once
more.
Drums
The holes for the tubes are then drilled
with special jig to obtain accurate
alignment of holes.
After the holes are drilled, the is then
reamed out to ensure the hole is circular
as possible
Drums
Drums
Water Drum
Steam Drum
Wrapper Sheet
Tube Sheet
Tube Sheet
Wrapper
Sheet
Drums
Manhole Plate
Manhole Opening
Drums
Why is the steam drum a larger diameter
then the water drum?
Drums
The steam drum contains a number of
drum internals where the water drum may
only contain a desuperheater.
The steam drum contains both water and
steam where the water drum only contains
water
Drums
Lets look at a 600 psia boiler.
The specific volume of water at 600 psig
is νf = 0.02013 ft3/lbm
The specific volume of steam at 600 psig
is νg = 0.70843 ft3/lbm
The expansion ratio is 35.19 to 1
Headers
In some boilers headers are used instead
of water drums.
The header serves the same function as
the water drum.
In general a drum is large enough so that
it can be entered by a man thru the
manhole
Headers
A header is smaller and access is
provided by means of hand holes and
hand hole plates located throughout the
length of the header, so that the tubes can
be inspected, cleaned and maintained, as
necessary
Type of Headers
Box type headers
Sinuous type headers
Circular type headers
Headers
Headers are usually used with:
Waterwall Tubes
Superheater Tubes
Economizer Tubes
Headers
Waterwall Tube
Downcomer
Headers
Handhole Plate
Handhole Opening
Gasket Seating Surface
Headers
Spiral Wound
Gasket
Dog