Good Engineering Practice for Northern Water and Sewer Systems

2.4 PIPE MATERIAL SELECTION CRITERIA
Selection of the pipe to use in a particular situation requires knowledge of the soil conditions on
the project. The pipe selected should closely meet the needs of the project and the end user. The
designers must recognize that the “perfect all-purpose pipe” does not exist.
Selection criteria should include:
• Corrosion Resistance Where water is aggressive, corrosion of metal pipe
interior walls can be substantial. Exterior corrosion,
primarily on uninsulated pipes, may also be a
concern if soils are aggressive.
• Roughness co-efficient (long term) A smooth pipe interior increases pipe capacity and
decreases pump energy requirements.
• Soil Conditions Buried pipes generally rely on bedding for support.
Loss of support can result in pipe collapse. Loss of
support can also lead to movement of reaction
blocks and separation of bell and spigot fittings.
• Beam Strength Where pipe must span between piles, (as in the
case of utilidors) or areas of thaw-induced
settlement, the pipe must have sufficient strength to
carry the loads.
• Freeze-Back Forces Excessive pore water pressure trapped between the
permafrost layer and winter frost layer can deform
or collapse pipe.
• Potential Freeze Damage Pipes should, if freezing risk is high, be capable of
being thawed and returned to service without loss of
strength.
• Overall Cost
Pipe selection should consider both the capital cost
(purchase plus installation) and the long term
operations and maintenance costs:
(i)
(ii)
Capital Cost
O & M Costs
• Purchase price.
• Special joining techniques add to installation
costs and costs of future repairs.
• Purchase price is affected by the wall thickness
of pipe that is selected. Designers must
calculate the required wall thickness for each
project.
• Where a municipality has standardized on one
pipe type, using a different type increases their
O & M costs and parts inventory.
GOOD ENGINEERING PRACTICE 2-5 Apr-04
Piping