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

Chapter 5 Water Infrastructure
Table 5-9 lists ductile iron pipe coating options. SPU requires a double cement mortar
lining thickness for ductile iron pipe. See AWWA C104 for more detail on cement mortar
linings for ductile iron pipe.
Table 5-9 Ductile Iron Pipe Coating Types for SPU Water System
Coating
Thermoplastic
Powder Coating
Wax Tape system
Polyethylene film
encasement (unbonded
film)
Fusion-Bonded
Epoxy, Polyurethane,
and Tape Coatings
SPU Preference
SPU standard coating for ductile iron (DI) pipe in a corrosive environment. See
Standard Spec 9-30.1(6)C. Can also be used on steel pipe.
When used with appropriate primer and a fiber reinforced outer wrap, this
coating can protect any buried metal surface, bolts, nuts, rods, copper, ductile,
steel, etc.
Common application for corrosion control. Acts as an environmental barrier to
prevent direct contact between pipe and corrosive soils. Not watertight;
groundwater can seep beneath the wrap. Integrity depends on proper installation,
careful handling by contractor, and inspection by owner. Polyethylene encasement
must be per Standard Spec 9-30.1(6) D. SPU has limited success using this
product.
Can be considered as an alternative coating system. Manufacturer has been
unwilling to apply bonded coating at factory. Design engineer should recognize
potential invalidation of pipe warranty if this is field applied.
C. Linings
Lining refers to a product used to protect the inside of a pipe from corrosion and
improve performance and service life. SPU requires a lining for all pipelines. All linings
must be National Sanitation Foundation (NSF) 61-approved.
Ductile iron pipe is typically supplied with a double thickness Portland cement-mortar
lining unless otherwise specified. See Standard Specification 9-30.1(1).
Welded steel pipe is furnished with two primary lining options: cement-mortar or
polyurethane. Cement mortar is a nominal thickness of ¼- to ½-inch. For interior linings,
polyurethane thickness is typically around 20-mils. See Standard Specification 9-30.1(1).
D. Cathodic Protection
Cathodic protection is a means of providing a sacrificial material to become the point
where corrosion occurs.
For a pipeline, cathodic protection provides a separate metal known as a sacrificial
anode to be the point where corrosion occurs. This anode protects the pipeline from
corrosion. By use of either an impressed current rectifier or materials that are
galvanically active (zinc or magnesium), the pipeline becomes the cathode and corrosion
is transferred to the anode.
See DSG Chapter 6, Cathodic Protection, for standards for cathodic protection systems.
E. Environmental Modifications
SPU employs corrosion control techniques such as modifying the pH at its water
treatment plants to reduce internal corrosion of water pipelines. This practice is
controlled by federal regulation under the Safe Drinking Water Act and EPA’s Lead and
Copper Rule and is a water quality operational methodology beyond the scope of this
DSG.
SPU Design Standards and Guidelines
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