SELECTION OF LINED SYSTEM :
The physical and chemical properties of the Fluoroplastic material to be used for lining is to be evaluated in terms of service requirement. Overall parameters for maximum operating temperature and pressure, along with corrosiveness of service fluid will determine liner and metallic shell material.
Chemical properties of the lining material will determine its compatibility with service fluid being handled under the specific operating condition of temperature and pressure. Correct processing technique & design parameters for the size of liner determine the overall performance of the lined items.
Physical properties of the lining materials and its processing technique will determine the reaction of liner to temperature / pressure combination vis-a-vis permeability and absorption capacity.
Permeation would cause corrosive fluid to attack the shell metal and corrode it even though the lining material itself is unaffected.
Gases and vapours permability through fluoroplastic material at a greater rate as pressure and temperature of the system becomes higher and higher. The molecules of gas and vapour migrate through the polymer, either by passing through microvoids in the polymer or by passing in between polymer molecules resulting in corrosion of shell and thereby failure of the system.
Process of permeability can be controlled by processing the liner as dense as possible. Higher the specific gravity of the liner, lesser the permeation. A typical example of high permeation is chlorine and hydrogen chloride gas under pressure and at elevated temperature.
CHEMICAL RESISTANCE :
All acids including Hydrofluoric, Sulphuric and Aqua regia.
- All Alkalies
- All Chlorides Acid, Organic and Inorganic
- All Sulphates, Organic and Inorganic
- All Solvents
- All Bleaching solutions
- All Peroxides
- All Phenols
- All Alcohols
- All Esters, Ether
- All Ketones
- And Acid Chlorides
Combined with chemical inertness of fluoropolymer, its unusual non-stick property, Fluoropolymer lined piping systems eliminate build up of deposits on the pipe walls which otherwise would reduce flow and effect operations.
Fluoropolymer lined piping systems have self sealing faces. This eliminates leakage between components and the use of extra sealing gaskets becomes redundant.
Fluoropolymer lined piping systems :-
- Have very high resistance to Thermal / Mechanical shock
- Are suitable for pressure and vacuum application
- Are easy to install
- Have long life
- Have zero maintenance
Theoretically minimum and maximum temperature for
- P.T.F.E -20°C to 260°C
- PFA -20°C to 260°C
- MFA -20°C to 240°C
- FEP -20°C to 205°C
Corrosion resistant to virtually all chemicals and solvents except fluorine and related compounds (Fluoride) and violent reducing agents, metallic sodium and molten alkali metals.
It can be used with aggressive media such as Hydrofluoric acid , pluoric acid, fuming sulphuric acid and nitric acid, hot sodium hydroxide solution, chlorine gas, hydrogen and nitric oxide.
ADVANTAGES OF LINED PIPING SYSTEM:
- Lined piping systems use materials such as glass, varieties of plastics, elastomers etc.
- A lined piping system offers many advantages over an equivalent uni-material pipe system.
- In a lined systems full advantage is taken of chemical resistance of liner and the mechanical strength of protective covering material.
- Many of the lining materials when used as solid pipes have limited allowable operating temperature and pressure parameters. These operating limits can be improved in a lined system by taking full advantage of the properties of its metallic shell.
- When relatively expensive material is used as a liner material the resultant lined piping system is less costly than the same installation using the lining material as a solid piping system.
- The mechanical properties are vastly improved by using an outside metallic shell, which also provides protection for the lining material preventing mechanical damage.
- The lining material and metallic shell expand and contract equal to that of the base metal of the outer shell because of the method of manufacture. This is an important characteristic of a lined pipe which is going to be exposed to a wide range of fluctuating temperatures.