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184 Chapter 5 Water Hydraulics, Transmission, and Appurtenances
steel pipes lined with cement or with bituminous enamel possess coefficients of 130 and
over on the basis of their nominal diameter; improved smoothness offsets the reduction in
cross-section.
Loss of capacity with age or, more strictly, with service depends on the properties of
the water carried and the characteristics of the pipe. Modern methods for controlling ag-
gressive water promise that the corrosion of metallic pipes and the disintegration of cement
linings and of reinforced concrete pipe will be held in check very largely, if not fully.
Cement and bituminous-enamel linings and reinforced-concrete and fiberglass pipes
do not, as a rule, deteriorate significantly with service.

5.8.2 Strength
Steel pipes can resist high internal pressures, but large lines cannot withstand heavy ex-
ternal loads or partial vacuums unless special measures are taken to resist these forces.
Ductile-iron and fiberglass pipes are good for moderately high water pressures and ap-
preciable external loads, provided that they are properly bedded. Prestressed reinforced-
concrete pipe is satisfactory for high water pressures. All types of concrete pipe can be
designed to support high external loads.

5.8.3 Durability
Experience with all but coated, ductile-iron pipe (length of life 100 years) has been too short
and changes in water treatment have been too many to give us reliable values on the length
of life of different pipe materials. The corrosiveness of the water, the quality of the material,
and the type and thickness of protective coating all influence the useful life of the various
types of water pipes. External corrosion (soil corrosion) is important, along with internal
corrosion. Pipes laid in acid soils, seawater, and cinder fills may need special protection.

5.8.4 Transportation

When pipelines must be built in rugged and inaccessible locations, their size and weight be-
come important. Ductile-iron pipe is heavy in the larger sizes; steel pipe relatively much
lighter. The normal laying length of cast-iron pipe is 12 ft (3.7 m). Lengths of 16.4, 18, and
20 ft (5, 5.5, and 6 m) are also available in different types of bell-and-spigot pipe. The length
of steel pipe is 20 to 30 ft (6 to 9 m). Both prestressed and cast reinforced-concrete pipe are
generally fabricated in the vicinity of the pipeline. The sections are 12 and 16 ft (3.6 to 4.9 m)
long and very heavy in the larger sizes. A diameter smaller than 24 in. (600 mm) is unusual.

5.8.5 Safety
Breaks in cast-iron pipes can occur suddenly and are often quite destructive. By con-
trast, steel and reinforced-concrete pipes fail slowly, chiefly by corrosion. However,
steel pipelines may collapse under vacuum while they are being drained. With proper
operating procedures, this is a rare occurrence. Fiberglass pipe fails suddenly, much
like cast-iron pipe.

5.8.6 Maintenance
Pipelines of all sizes and kinds must be watched for leakage or loss of pressure—outward
signs of failure. There is little choice between materials in this respect. Repairs to precast