2000 Hook-up Book - Spirax Sarco

Draining Steam Mains
Note from the example that in
most cases, other than large distribution
mains, 1/2" Thermo-
Dynamic ® traps have ample
capacity. For shorter lengths
between drip points, and for small
diameter pipes, the 1/2" low
capacity TD trap more than meets
even start up loads, but on larger
mains it may be worth fitting parallel
1/2" traps as in Fig. II-6 (page
86). Low pressure mains are best
drained using float and thermostatic
traps, and these traps can
also be used at higher pressures.
The design of drip stations
are fairly simple. The most common
rules to follow for sizing the
drip pockets are:
1. The diameter of the drip pockets
shall be the same size as
the distribution line up to 6
inches in diameter.The diameter
shall be half the size of the
distribution line over 6 inches
but never less than 6 inches.
Steam Trap
2. The length of the drip pocket
shall be 1-1/2 times the diameter
of the distribution line but
not less than 18 inches.
Drip Leg Spacing
The spacing between the
drainage points is often greater
than is desirable. On a long horizontal
run (or rather one with a
fall in the direction of the flow of
about 1/2" in 10 feet or 1/250)
drain points should be provided at
intervals of 100 to 200 feet.
Longer lengths should be split up
by additional drain points. Any
natural collecting points in the
systems, such as at the foot of
any riser, should also be drained.
A very long run laid with a fall
in this way may become so low
that at intervals it must be elevated
with a riser. The foot of each of
these “relay points” also requires a
collecting pocket and steam trap.
Fall 1/2" in 10 Ft Steam
Steam Trap
Condensate
Figure 5
Draining and Relaying Steam Main
Steam Trap
Draining Steam Mains
Sometimes the ground contours
are such that the steam
main can only be run uphill. This
will mean the drain points should
be at closer intervals, say 50 ft.
apart, and the size of the main
increased. The lower steam
velocity then allows the condensate
to drain in the opposite
direction to the steam flow.
Air venting of steam mains is
of paramount importance and is
far too often overlooked. Steam
entering the pipes tends to push
the air already there in front of it
as would a piston. Automatic air
vents, fitted on top of tees at the
terminal points of the main and
the larger branches, will allow discharge
of this air. Absence of air
vents means that the air will pass
through the steam traps (where it
may well slow down the discharge
of condensate) or through
the steam using equipment itself.
Steam Trap
Case in Action: Steam Main and Steam Tracing System Drainage
The majority of steam traps in refineries are installed on
steam main and steam tracing systems. Thorough
drainage of steam mains/branch lines is essential for effective
heat transfer around the refinery and for waterhammer
prevention. This holds true for condensate drainage from
steam tracing lines/jackets, though some degree of backup
(or sub-cooling) is permissible in some applications.
The predominant steam trap installed is a nonrepairable
type that incorporates a permanent pipeline
connector. Scattered throughout the system are a number
of iron and steel body repairable types.
Most notable failure of steam traps are precipitate formation
on bucket weep-holes and discharge orifices that
eventually plugs the trap shut. A common culprit is valve
sealing compound injected into leaking valves which forms
small pellets that settle in low points, such as drip
legs/steam traps and on strainer screens making blow
down difficult. This problem also occurs during occasional
“system upset” when hydrocarbon contaminants are mistakenly
introduced to the steam system.
A noise detector and/or a temperature-indicating
device is required to detect trap failure. Especially costly is
Steam Trap
the fact that operators are not allowed to remove traps for
repair when threading from the line is required.
Maintenance personnel must be involved.
Solution
Universal connector steam traps were installed for trial in
one of the dirtiest drip stations at the refinery. The traps
held up under adverse operating conditions requiring only
periodic cleaning. Since the time of installation, all failed
inverted bucket traps in this service were replaced with universal
connector traps. Strainers were installed upstream
of each.
Benefits
• The addition of Thermo-Dynamic ® traps allowed for easier
field trap testing.
• The addition of universal connectors significantly
reduced steam trap installation and repair time.
• 33% reduction in steam trap inventory due to standard
trap for all sizes.
• Reduced energy loss is significantly reduced using Thermo-
Dynamic ® steam traps versus original inverted bucket traps.
11
SYSTEM DESIGN