2013 Water System Plan, Volume II - Seattle City Clerk's Office - City ...

pipe. The annular space between the two pipes is sometimes filled with grout. The design
engineer should carefully consider the hydraulic implications of reducing the pipeline diameter.
5.6.5.2 Relining
If video inspection of the pipeline interior shows significant deterioration of the lining, relining
of the pipe may be possible. Pipes are relined by thoroughly cleaning the existing pipe interior
then using a machine to spray-coat new cement mortar lining inside the pipe. The method used
depends on pipe size. The relining can be designed to strengthen the pipe through use of a
structural mesh embedded in the spray-coated cement mortar lining.
5.6.5.3 Cathodic Protection
Cathodic protection is one method SPU uses to rehabilitate existing water pipelines. For more
detail on cathodic protection for distribution and feeder mains, see DSG section 5.6.8 and DSG
Chapter 6, Cathodic Protection.
5.6.6 Emergency Pump Connections
In some emergencies, a connection between two nearby pipelines may be needed. If the
pipelines operate in different pressure zones, then a pump may be needed between the two
lines. If possible, use an existing interconnection. If no inter-connecting pipe structure is
available, SPU recommends using a nearby blow-off location and installing a pump between the
two pipelines.
5.6.7 SCADA
See DSG Chapter 10, Instrumentation & Control, for SCADA system design. The design engineer
should consider whether any monitoring or controls are needed and if the controls should be
linked to the system wide SCADA system.
5.6.8 Corrosion Control
Corrosion control of SPU pipelines comes from both active and passive protection systems. Bare
metal steel or ductile iron pipe will rust when exposed to corrosive soils or water if no
protection system is installed. The rate of corrosion depends on the corrosivity of the
environment (typically soil or water). The rate of corrosion is mostly a function of how well the
environment conducts electrical current.
Resistivity plays a key role in corrosion control of pipelines. Resistivity refers to the resistance of
the environment to promote electrical current flow. When the resistivity of water or soil is high,
less current can flow through that environment and the rate of corrosion is lower. For internal
corrosion (inside of pipes), water resistivity is constant. For external corrosion (exterior surfaces
of pipes), soil resistivity is highly variable. SPU GIS maps show the results of tests taken to date
for soil resistivity. SPU staff can test for specific areas for soil resistivity.
The internal corrosion of pipes is managed through a combination of water chemistry
adjustments and the use of internal linings..
SPU controls external (on the soil-pipe interface) corrosion through one of three methods:
1. Testing the soil environment for resistivity
5-36 SPU Design Standards and Guidelines