Page 68 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

PIPING

2.18 CHAPTER TWO

The chemical resistance of the various types of plastics varies greatly not only among
different types of plastic, but among different grades of the same type of plastic. Achieving
full resistance is a function of the resistance of the compound used to make the pipe and
the processing of the plastic.
The factors that determine the suitability and service life of any specific plastic pipe are
1. The specific chemicals and their concentrations
2. The jointing method
3. Dimensions of the pipe and fittings
4. Pressure inside the pipe
5. Ambient temperature and temperature of the fluid
6. Period of contact
7. Stress concentrations in the pipe and fittings

Abrasion
If a material such as sand, gravel, or slurry is transported in the piping system, or frequent
cleaning with mechanical equipment is anticipated, resistance to abrasion should be inves-
tigated. Mechanical cleaning equipment manufacturers have data available from tests on
various piping materials. Pipe manufacturers are also a source of information regarding
various effluents. Additives can be used to increase the abrasion resistance of any pipe.

Biological Resistance
Very few types of plastic pipe can be degraded and/or deteriorated by the action of micro-
or macroorganisms. For the most part, plastic pipe shows negligible or no susceptibility to
bacterial attack. Refer to manufacturers for specific data.

Electrical Properties
Because plastic pipe is nonconductive, electrostatic charging of a pipeline is possible if
dry, electrically nonconductive material is transported. All pipe materials with a specific
resistance of 106 ohms per centimeter (Ω/cm) are considered nonconductive. Plastic pipe
is generally not recommended to carry ignitable mixtures or electrically nonconductive dry
substances due to potential electrostatic charging and possible damage to the dry material
inside the pipe.
Static electrical charges can be prevented by providing the pipe with a conductive coating
of metallic powder or lagging the pipe with metallic foil that has been grounded.

PERMEABILITY

Permeation is a process where fluids pass either into or out of a piping system through
the walls of a pipe. Permeation can occur through the walls of a susceptible plastic pipe,
through gaskets or other jointing material, and through defects or inappropriately or incor-
rectly sealed pipe.
Organic matter that migrates from soil through the plastic pipe is called permeate, and
the process is called permeation. Until additional scientific work is completed on permeation

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