Epoxies.
Epoxy resins are strong and have good
resistance to solvents, salts, caustics, and dilute acids. Epoxies
are cross-linked by curing agents which become an integral part of
the polymer and affect the thermal, chemical, and physical properties
of the polymer.
For instance, the maximum service
temperature of epoxy pressure pipe cured with anhydrides is 180°F
(83°C), and it has little resistance to caustics; that cured with
aromatic amines can be used at temperatures above 225°F (107°C),
and it has good caustic resistance.
The major use of epoxy pipe is in oil
fields, where its resistance to corrosion and paraffin buildup makes
it preferable to steel pipe for crude-collection and
saltwater-injection lines. Other uses are in the chemical process
industry, in heating and air conditioning, in food processing, for
gasoline and solvents, and in mining applications (including abrasive
slurry transport, communications ducts, and power conduits).
Polyesters.
Although typically not as strong as the
epoxies, polyesters offer good resistance to mineral acids, bleaching
solutions, and salts.The most commonly used polyester resins for pipe
are isophthalic polyesters and bisphenol A fumarate polyesters.
Isophthalics have poorer resistance to
caustics and oxidizers. Bisphenol A fumarates have improved
resistance to these materials and are widely used in paper mills for
bleach lines.
Isophthalic resin pipe is used in
waste-treatment and power plants in services where corrosive
conditions are not severe. Maximum operating-temperature limits for
pressure pipe vary, depending upon the specific material, but are
generally below 200°F (93°C).
Vinyl Esters.
These resins include chemical features
of both epoxies and polyesters. Vinyl ester resins offer better
chemical resistance, somewhat higher temperature limits, and better
solvent resistance than ordinary polyesters but generally do not
compare to epoxies in these properties.
Vinyl ester resins are preferred over
polyesters because they are more chemical resistant than the
isophthalics and less brittle than the bisphenol A fumarates.Typical
services are in fertilizer plants (acid lines), chlorine plants
(chlorine-saturated brine lines), and paper mills (caustic and
black-liquor lines).
Furans.
Furan resins offer very good chemical,
solvent, and temperature resistance—up to about 300°F (150°C).
Because they extend the limitations of the other resins, they are
often selected for use in the processing industries in place of
exotic metal piping.
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