Plastic Lined Pipe

1.     Reasons for lining

Protect pipeline system from corrosion is essential to prevent leaks and consequent possible environment disasters, fire and explosion, personal injury, service disruption and costly maintenance.

Metallic pipe is strong, easy to work with and inexpensive, but even mildly corrosive fluids can rapidly eat it away, from the inside out, severely limiting its lifespan. Nonmetallic piping, fiberglass and thermoplastics, do not have the physical strength of metallic piping, but has excellent chemical resistance.

Plastic lined piping combines the best of both common piping systems into one. This is excellent for handling acids, corrosives and hazardous materials. Plastic lined pipe can be fabricated with either a loose or locked in liner, however, a locked in liner reduces the effect of the difference in expansion coefficient between the metal and the liner.

     2.     Commonly Used Liner Types

Polytetrafluoroethylene (PTFE): Originally developed by DuPont. It maintains high strength, toughness and self-lubrication at low temperatures down to 5 K (−268.15 °C; −450.67 °F), and good flexibility at temperatures above 194 K (−79 °C; −110 °F) with chemical inertness.

Perfluoroalkoxy (PFA): A chemically modified polymer of PTFE that exhibits the same chemical resistance and temperature handling capabilities as PTFE.

Fluorinated Ethylene Propylene (FEP): The first melt processible resin that matched the chemical resistance of PTFE.

Ethylenetetrafluoroethylene (ETFE): ETFE can be specified for lower service temperature in conjunction with stainless steel housing.

Polyvinylidene Fluoride (PVDF): PVDF is widely used for piping conveying halogenated compounds but should not be used in any service where the PH is above 11.

Polypropylene (PP): PP is generally used to convey inorganic acids such as hydrochloric and sulfuric as well as caustics such as sodium hydroxide.

Polyvinylidene Chloride (PVDC): PVDC has the lowest temperature limit, found widespread used in the water treatment and pulp and paper industries for its particularly food chemical resistance towards chloride.

3.     Temperature Limitation

All plastic lined piping systems have a minimum and maximum use temperature. These temperature limitations are always well below the melt temp. of the liner materials.

Table 1. Temperature Specifications

Material	Temp. Range, ℉ (℃)
PTFE	-20~500 (-29~260)
PFA	-20~500 (-29~260)
FEP	-20~300 (-29~149)
ETFE	-20~300 (-29~149)
PVDF	-20~275 (-29~135)
PP	0~225 (-18~107)
PVDC	0~175 (-18~79)