3.4 Pitch of Underground Steam Lines. To provide easy drainage, steam lines
are pitched down at a minimum of 3 inches per 100 feet of length in the
d i r e c t i o n of steam flow. Where the ground" surface slopes in a direction
o p p o s i t e to the steam flow in the pipes, t h e underground lines are generally
s t e p p e d up in vertical risers at drip points in manholes and then pitched down
t o the next drip point. T h i s method is also used for very long horizontal
r u n s to keep the line within a reasonable range of elevations.
c o u n t e r f l o w conditions, refer to paragraph 2.6.
3 . 5 Conduit Systems. C o n d u i t systems are single or multiple pipe systems
t o t a l l y enclosed in a waterproof structure. T h e piping is firmly supported .
and anchored, but is free to expand and contract following temperature changes
w i t h o u t damaging the insulation or casing. Necessary pipe supports, guides,
a n c h o r s , expansion joints, a n d fittings are provided (refer to chapter 7).
Conduit systems are designed to permit drainage of the conduit in place and to
p e r m i t drying of the insulation if the system is flooded. This is especially
i m p o r t a n t in areas of heavy rainfall and where the water table is likely to be
h i g h for several days. Conduit systems are classified as A or B types,
d e p e n d i n g on the following criteria.
(a) Class A Sites and Systems. These systems include any site where
w a t e r , or the water table, is expected to be above the bottom of the conduit
at any time. I n this system, t h e r e is always a possibility for saturated
g r o u n d above any part of the conduit structure.
(b) Class B Sites and Systems. These systems include any site where
w a t e r , or the water table, does not rise above the bottom of the system.
C l a s s B sites are usually areas where the soil is coarse grained, which
3 . 6 Class A Conduits. Class A conduits are used exclusively in Class A
s i t e s . T h e y must satisfy the following requirements:
( a ) Water tightness as determined by the field air pressure test (refer
t o section 4 of this chapter)
( b ) Free air passage suitable for drying the insulation if it becomes wet
( c ) Designed to permit air pressure testing at any time (refer to
s e c t i o n 4)
(d) Capability of being drained in place, if required
( e ) Capability to withstand 20-psig air pressure applied between the
i n s u l a t i o n and outer casing,