REV1 RESUB 1 - HydraulicsManual - Zone IIPipe Classifications and Materials
When selecting a pipe alternative, the designer should always keep in mind
the degree of difficulty that will be encountered in replacing a pipe at a future date.
Drain pipes are placed relatively shallow and are easy to replace. Culverts tend
to have more depth of cover and pass under the highway alignment making them
more difficult to replace. Storm sewers are generally utilized in congested urban
areas with significant pavement cover, high traffic use, and a multitude of other
buried utilities in the same vicinity. For these reasons, storm sewers are generally
considered to be the most expensive and most difficult to replace and should have a
long design life. These are generalities that will serve as guidelines to the designer.
When special circumstances exist (i.e., extremely high fills or extremely expensive
structure excavation) the designer should use good engineering judgment to justify
the cost effectiveness of a more expensive pipe option or a higher standard
of protective treatment than is recommended on the Figures in this Section.
8-4.1 Corrosion Zone I
With the exceptions noted below, Corrosion Zone 1 encompasses most of Eastern
Washington and is considered the least corrosive part of the state. Plain galvanized
steel, untreated aluminized steel, aluminum alloy, thermoplastic, and concrete pipe
may all be used in Corrosion Zone I. See Figures 8AIA and B for a complete listing
of all acceptable pipe alternates for culvert and storm sewer applications. Treatment
1, 2 or 5 is required for all storm sewers if the seams are not pressure testable
(ungasketed lock seam).
Parts of Eastern Washington, which are not in Corrosion Zone I are placed into
Corrosion Zone II. They include:
Okanogan Valley
Pend Oreille Valley
Disautel Nespelem Vicinity
WSDOT Hydraulics Manual M 23-03.01 Page 8-21
July 2008
Pipe Classifications and Materials
8-4.2 Corrosion Zone H
Most of Western Washington, with the exceptions noted below, along with the three
areas of Eastern Washington identified above make up Corrosion Zone II. This is an
area of moderate corrosion activity. Generally, Treatment 2 is the minimum needed
to provide corrosion protection for galvanized steel culverts and storm sewers.
Untreated aluminized steel, aluminum alloy, thermoplastic, and concrete pipe may
be used in Corrosion Zone II. See Figures 8.4.2A and B for a complete listing of all
acceptable pipe alternates for culvert and storm sewer applications.
Parts of western Washington, which are not located in Corrosion Zone II, are placed
into Corrosion Zone III. They include:
1. Whatcom County Lowlands, described by the following:
a. SR 542 from its origin in Bellingham to the junction of SR 9;
b. SR 9 from the junction of SR 542 to the International boundary; and
c. All other roads and areas lying northerly and westerly of the above described
routes.
2. Lower Nisqually Valley.
3. Low-lying roadways in the Puget Sound basin and coastal areas subjected
to the influence of saltwater bays, marshes, and tide flats. As a general guideline,
this should include areas with elevations less than 20 feet (6 meters) above
the average high tide elevation. Along the Pacific coast and the Straits of Juan de
Fuca, areas within 300 to 600 feet (100 to 200 meters) of the edge of the average
high tide can be influenced by salt spray and should be classified as Corrosion
Zone III. However, this influence can vary significantly from location to location,
depending on the roadway elevation and the presence of protective bluffs
or vegetation. In these situations, the designer is encouraged to evaluate existing
pipes in the vicinity of the project to determine the most appropriate corrosion
zone designation.
8-4.3 Corrosion Zone 111
The severely corrosive areas identified above make up Corrosion Zone III. Concrete
and thermoplastic pipe are allowed for use in this zone without protective treatments.
Aluminum alloy is permitted only as described in Section 8-2.2.6. See Figures 8.4.3A
and B for a complete listing of all acceptable pipe alternates for culvert and storm
sewer applications.
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July 2008
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