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

All steel pipe must have bonded coating for all soil conditions
Additional corrosion protection may be required where stray current is present (i.e. rail transit)
If bonded coating cannot be provided where required, pipe can be installed bare and additional anodes
supplied at SPU engineer’s direction; impressed current cathodic protection may be required.
5.6.8.2 Coatings
Coating refers to products applied to the outside of pipes. Steel and ductile iron pipelines have
different coating requirements. Before selecting a coating system, soil sampling (resistivity
testing) should be completed to determine the corrosive nature of the soil.
A. Steel Pipe Coatings
All steel pipes must be coated. Several different coating options are available. The
design engineer should use best judgment in deciding among coatings. Table 5-8 lists
coating types found in the SPU water system in order of use and preference.
Table 5-8 Steel Pipe Coating Types for SPU Water System
Coating
Polyurethane
Coating
Fusion Bonded
Epoxy (FBE)
Paint Coatings
Heat Shrink
Wrap Sleeve
Tape Coating
Cementmortar
Coating
Coal-tar
Enamel
Coating
Description
SPU standard for steel pipe coating. This is a thin film bonded dielectric coating with
both water and chemical resistance. It is typically factory-applied and thickness is
customized to a specific application. Surface preparation and curing process is very
critical.
FBE is typically applied at the factory on the pipe, and field applied on the joints.
Applied by heating the steel pipe, then blowing epoxy in powder form on the heated
pipe. Generally considered one of the most durable coatings. Typically most costly.
Paint systems work well with cathodic protection systems. Resilient and extremely
abrasion resistant. Paint coatings are applied according to AWWA C210 and C218.
Commonly used where there is minor damage to the existing coating or the extent of
damage is small.
Tubular sleeves that can provide effective coating protection around field-welded
joints. It is field-applied. Known to be reliable and effective against thermal, chemical,
and environmental attack. Economical due to ease of application and no need for
primer.
Most commonly specified dielectric coating systems. Has a good performance record
at reasonable cost. Typical application includes 80-mil cold-applied plastic tape in three
layers over a properly prepared steel surface.
No longer used, but may be encountered on existing pipes. Chemically protects pipe
from corrosion by providing an alkaline environment where oxidation of steel is
inhibited. Can be applied in various thicknesses. Provides mechanical protection against
handling and installation damage. Typical application thickness is 1inch.
One of oldest methods to provide corrosion protection for steel pipelines. Coal-tar
enamel is applied over a coal tar or synthetic primer. Application includes cleaning,
priming, application of hot enamel, and covering of a fiberglass matte and/or felt outer
wrap. Recommended application includes 7/32-inch coal tar with fiberglass reinforced
mineral felt with heat-shrinkable cross-linked polyolefin sleeves at joints.
B. Ductile Iron Pipe
Due to its thickness, ductile iron pipe does not always need a coating. It generally only
needs coating when soil conditions warrant. Soils should be tested to identify that need.
For ductile iron pipe, the standard factory coating is an asphaltic coating approximately
1-mm thick. This coating minimizes atmospheric oxidation, but provides no in-ground
protection.
Ductile iron pipe must conform to Standard Specification 9-30.2(1).
5-38 SPU Design Standards and Guidelines