Polyethylene exhibits awiderange of corrosionresistance—ranging from
potable water to corrosive wastes. It is resistant to most minerala cids,
includings ulfuricu pt o7 0% concentration, inorganic salts including
chlorides, alkalies, and manyo rganic acids.
It is notr esistant to bromine, aromatics, or chlorinated hydrocarbons.
Refert oT able 6.23 fort he compatibilityo fE HMWPE with selected
corrodents andT able 6.24 forH MWPE’s compatibility. Reference [1]
provides am ore comprehensive listing.
6.6.6 Tetrafluoroethylene
Tetrafluoroethylene (PTFE) can be used continuouslya t5 008 F( 2608 C). It
cannotb eb ondedd irectly to metal substrates, but it can be bondedw ith a
laminated fiberglass sheetasab acking.
The material tends to creep under stress at elevatedt emperatures. When
the vessel is designed,provisions should be madetoretain the PTFE. PTFE
liners aresubject to permeation by somecorrodents. Table 6.25 provides the
vapor permeation of PTFE by selected materials.
PTFE is chemically inert in the presence of most corrodents. There are very
few chemicals that will attack it within normal use temperatures. These
reactants are among the most violent oxidizersand reducing agents known.
Elemental sodiumi ni ntimate contact with fluorocarbons removes fluorine
from the polymer molecule. The other alkali metals (potassium,lithium,etc.)
react in as imilar manner.
Fluorinea nd related compounds( e.g., chlorinet rifluoride) area bsorbed
into the PTFE resin with such intimatec ontact that the mixture becomes
sensitive to as ource of ignition such as impact.
The handling of 80% sodium hydroxide, aluminumc hloride, ammonia,
and certain amines at high temperatures may produce the same effect as
elemental sodium. Also slow oxidative attack can be produced by 70% nitric
acid underpressureat4808 F( 2508 C).
Refer to Table 6.26 for the compatibility of PTFE with selected corrodents.
Reference [1]p rovides listing of additional corrodents.
6.6.7 Fluorinated Ethylene Propylene
Fluorinated ethylene propylene (FEP) has al ower maximum operating
temperature than PTFE. It exhibits changesi np hysical strength after
prolonged exposure above4 008 F( 2048 C). Therefore, the recommended
maximum continuous operating temperature is 3758 F( 1908 C).
Permeation of FEP liners can pose ap roblem. Table 6.27 provides some
permeation data relating to the more common chemicals. There is also
some absorption of chemicals by FEP.T hisa bsorption can also lead to
problems. Table6 .28 is al isting of the absorption of selected liquids
by FEP.
Sheet Linings
367
CAT8247—CHAPTER 6—6/10/2006—12:30—SRIDHAR—XML MODEL B–pp. 287–402
potable water to corrosive wastes. It is resistant to most minerala cids,
includings ulfuricu pt o7 0% concentration, inorganic salts including
chlorides, alkalies, and manyo rganic acids.
It is notr esistant to bromine, aromatics, or chlorinated hydrocarbons.
Refert oT able 6.23 fort he compatibilityo fE HMWPE with selected
corrodents andT able 6.24 forH MWPE’s compatibility. Reference [1]
provides am ore comprehensive listing.
6.6.6 Tetrafluoroethylene
Tetrafluoroethylene (PTFE) can be used continuouslya t5 008 F( 2608 C). It
cannotb eb ondedd irectly to metal substrates, but it can be bondedw ith a
laminated fiberglass sheetasab acking.
The material tends to creep under stress at elevatedt emperatures. When
the vessel is designed,provisions should be madetoretain the PTFE. PTFE
liners aresubject to permeation by somecorrodents. Table 6.25 provides the
vapor permeation of PTFE by selected materials.
PTFE is chemically inert in the presence of most corrodents. There are very
few chemicals that will attack it within normal use temperatures. These
reactants are among the most violent oxidizersand reducing agents known.
Elemental sodiumi ni ntimate contact with fluorocarbons removes fluorine
from the polymer molecule. The other alkali metals (potassium,lithium,etc.)
react in as imilar manner.
Fluorinea nd related compounds( e.g., chlorinet rifluoride) area bsorbed
into the PTFE resin with such intimatec ontact that the mixture becomes
sensitive to as ource of ignition such as impact.
The handling of 80% sodium hydroxide, aluminumc hloride, ammonia,
and certain amines at high temperatures may produce the same effect as
elemental sodium. Also slow oxidative attack can be produced by 70% nitric
acid underpressureat4808 F( 2508 C).
Refer to Table 6.26 for the compatibility of PTFE with selected corrodents.
Reference [1]p rovides listing of additional corrodents.
6.6.7 Fluorinated Ethylene Propylene
Fluorinated ethylene propylene (FEP) has al ower maximum operating
temperature than PTFE. It exhibits changesi np hysical strength after
prolonged exposure above4 008 F( 2048 C). Therefore, the recommended
maximum continuous operating temperature is 3758 F( 1908 C).
Permeation of FEP liners can pose ap roblem. Table 6.27 provides some
permeation data relating to the more common chemicals. There is also
some absorption of chemicals by FEP.T hisa bsorption can also lead to
problems. Table6 .28 is al isting of the absorption of selected liquids
by FEP.
Sheet Linings
367
CAT8247—CHAPTER 6—6/10/2006—12:30—SRIDHAR—XML MODEL B–pp. 287–402