smooth finish over which asbestos or glass cloth
Observe the following general precautions in the
lagging may be applied (fig. 15-27).
application and maintenance of insulation:
Removable insulation is usually installed in the
1. Fill and seal all air pockets and cracks.
Failure to do this will cause large losses in
the effectiveness of the insulation.
Manhole covers, inspection openings, turbine
2. Seal the ends of the insulation and taper off
c a s i n g flanges, drain plugs, strainer
to a smooth, airtight joint. At joint ends or
cleanouts, and spectacle flanges
other points where insulation is liable to
damage, use sheet metal lagging. Cuff
Flanged pipe joints adjacent to machinery or
flanges and joints with 6-inch lagging.
equipment that must be broken when units
are opened for inspection or overhaul
3. Keep moisture out of all insulation work.
Moisture is an enemy of heat insulation fully
Valve bonnets of valves larger than 2 inches
as much as it is of electrical insulation. Any
NPS that operate at 300 psi and above, or at
240°F and above
All pressure-reducing and pressure-regulating
4. Insulate all hangers and other supports at
valves, pump pressure governors, and
their point of contact from the pipe or other
unit they are supporting. Otherwise, a
considerable quantity of heat will be lost via
A small unit of machinery or equipment, such as
conduction through the support.
an auxiliary turbine, requires a different approach.
It would be difficult to install both permanent
5. Keep sheet metal covering bright and
insulation over the casing and removable and
unpainted unless the protecting surface has
replaceable c o v e r s over the casing flanges.
Therefore, the entire insulation may be made
from bright-bodied and light-colored objects
removable and replaceable. Covers should fit
accurately and should project over adjacent
Figure 15-27.--Permanent-type insulation of pipe fittings, flanges, and valves.