5-06M
a complete engineering analysis of the system is performed in regard to
ability to accept increased thermal expansion, increased pressures and
temperatures.
5.3 Connecting to Existing Steam Distribution Systems: Calculate steam flows
and pressure drops on the portions of the existing system which are affected
by the new steam loads. The new steam loads must not impose excessive
pressure drops or velocities on the existing systems.
5.4 Sloping and Dripping of Steam Lines:
5.4.1 Steam lines shall pitch down 50 mm in 12 meters (two inches in 40 feet)
in the direction of flow. Provide drip pockets and steam traps at all risers
and immediately ahead of all isolation valves that would collect condensate if
the valves are closed. Distance between drip pockets shall not exceed 150
meters (500 feet) and should be less if possible. Locate all drip pockets and
steam traps in manholes or buildings. Provide oversized drip pockets (refer to
standard detail). Steam drip traps should discharge into a drip return line
which is separate from other types of condensate return lines such as pumped
returns and vacuum returns.
Caution: Water hammer is dangerous and must be prevented.
It can occur
when condensate is not properly removed from steam lines.
Steam lines must
be properly sloped and drained.
5.4.2 Steam traps for steam line drip service must handle normal steady state
radiation and convection heat loss condensate and also high levels of
condensate and air flow when the steam line is being warmed-up. The preferred
trap type is the inverted bucket type with thermal vent (for air release on
warm-up) in the bucket. This type is resistant to water hammer and wire
drawing of the valve and seat. Caution must be exercised when sizing the traps
because oversized traps can "blow-through" (fail open) and lose their prime.
Caution: Fixed orifice steam traps with no operating mechanism should not
be applied on steam line drip service. VA experience is that the small
diameter orifices become plugged with dirt and the trap fails closed. This
will cause build-up of condensate in the steam main and dangerous water
hammer may occur.
5.5 Condensate Return: Generally, all condensate should be collected at
condensate return pump sets and then be pumped to the boiler plant.
Exceptions include existing systems being replaced which have other types of
condensate returns such as vacuum or gravity. Also drip returns from the steam
line drip traps may be returned directly to the boiler plant if practical.
5.6 Thermal Expansion:
so that piping will not be overstressed. The locations must be shown. Sizes
of bends and loops need not be shown on direct buried systems because the
system manufacturer is responsible for loop and bend sizing. Expansion loops
should be used instead of expansion joints whenever possible. This is because
expansion joints can fail.
5.6.2 Pipe anchors should be provided within 0.6 to 1.5 meters (two to five
feet) outside of manhole walls to minimize pipe movement through the manhole.
For piping which passes through the manhole, do not anchor on both sides of
the manhole unless the piping within the manhole has sufficient offset to
avoid overstress. Thermal expansion stress calculations must always be
conducted to ensure proper anchor locations throughout the system. Those
calculations must also account for the pipe expansion in the manholes.
5.6.3 All anchoring and expansion joints, bends and loops must be completely
designed and specified in the contract documents except for anchors and
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