VENT HOLES
Webster defines "vent" as a small aperture designed
to provide an outlet from a confined space. One lined pipe manufacturer
says that vent holes are essential to release gasses which may
be generated at elevated temperatures and trapped between the
liner and housing before it collapses the liner. They vent all
their lined systems. ASTM F1545 for lined pipe says in point
5.3 that each pipe and fitting shall be provided with a venting
system that will release any pressure between the liner and
the housing. Note 8 states that venting is not required with
PVDF, PP, ETFE, or PVDC liners. The key word here is RELEASE.
The EPA and other governmental agencies are passing regulations
and laws to limit or stop atmospheric releases of volatile organic
compounds (VOC's). VOC's are among the most common pollutants
emitted by the chemical process industry. VOC's are carbon compounds
that react with nitrogen oxides and other airborne chemicals
in the presence of sunlight (photochemically) to form ozone,
which is a primary component of smog. Reductions of VOC emissions
in areas that exceed the current national ambient air quality
standard for ozone of 0.12 ppm is mandated under Title I of
the Clean Air Act Amendments of 1990. In addition, Title III
of the amendments requires reduction of the emission of 189
hazardous air pollutants, most of which are included under the
definition of VOC's as well. With all of the above requirements
and concerns with cleaning up the air, does it make any sense
to vent lined pipe? (About as much sense as drilling holes in
the containment surrounding a nuclear reactor.)
In the beginnings of Lined Pipe, vent holes were
necessary only for PTFE and FEP due to liner thickness of .050"or
less which allowed gasses to easily permeate and build up between
the liner and the pipe collapsing the liner. Today our liner
thickness is 3 to 4 times as thick greatly reducing the migration
of gasses through the liners even in more easily permeated PTFE.
We at Fusibond only vent our PTFE and PFA liner systems. All
others are vent free. This allows your customers a choice of
liners that won't contribute to the problem of poor air quality
and this needs to be communicated to them.
Our heavy wall PFA liners could be manufactured
without vent holes, but ASTM F1545 mandates that they be vented.
The chance of a gas permeating today's thicker liners in sufficient
quantity to collapse the liner we believe is relatively small.
The release of those same chemicals into the atmosphere through
a venting system would have more far reaching consequences than
the collapse of a pipe liner. This is especially true if the
liner itself fails and the pipe starts showering acid all over.
I'm sure your customer's safety personnel would not approve
of this.
Most of the information on permeation of PTFE
and FEP available today is out of date. It was taken from testing
done on thin films and may not reflect what is required in the
Chemical Process Industry. Our PFA liners are by far less easily
permeated than the PTFE liners used in the past. We at Fusibond
are taking the position that other liner systems should be used
instead of vented systems. This will help eliminate one source
of fugitive emissions and reduce air pollution. If any of your
customers would like to test unvented PFA we will be happy to
work with them.
For your information, here are the liners that
our competition vents: Resistoflex: Currently vents all of their
liner systems. Dow: Currently vents PTFE and PVDF liner systems.
3P: Currently vents FEP, PFA, and PTFE liner systems.
For more information on which liner systems can
handle your particular services without vent holes contact the
factory.
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