Corrosion of Linings
185
to which the backup RTP is exposed has been reduced in addition to preventing the RTP from being exposed to the chemicals in the process system. An
upper temperature limit for using RTP dual laminates is 350°F (177°C).
The dual laminate construction lessens the problem of permeation through
liners. If there is a permeation, it is believed to pass through the RTP structure
at a rate equal to or greater than through the fluoropolymer itself, resulting
in no potential for collection of permeate at the thermoplastic-to-thermoset
interface. If delamination does not occur, permeation is not a problem.
6.2.2 Considerations in Liner Selection
Before selecting a lining material, give careful consideration to several broad
categories, specifically materials being handled, operating conditions, and
conditions external to the vessel.
The following information must be known about the materials being
handled:
1. What are the chemicals being handled and at what concentrations?
2. Are there any secondary chemicals, and if so, at what concentration?
3. Are there any trace impurities or chemicals?
4. Are there any solids present? And if so, what are their particle sizes
and concentrations?
5. If a vessel, will there be any agitation, and to what degree? If a pipeline, what are the flow rates (minimum and maximum)?
6. What are the fluid purity requirements?
The answers to the above questions will narrow the selection to those materials that are compatible. This next set of questions will narrow the selection
further by eliminating the materials that do not have the required physical
or mechanical properties.
1. What is the normal operating temperature and temperature range?
2. What peak temperatures can be reached during shutdown and
startup, process upset, etc.?
3. Will any mixing areas exist where exothermic or heat-of-mixing
temperatures can develop?
4. What is the normal operating pressure?
5. What vacuum conditions and range are possible during operation,
startup, shutdown, or upset conditions?
6. Will there be temperature cycling?
7. What cleaning methods will be used?
185
to which the backup RTP is exposed has been reduced in addition to preventing the RTP from being exposed to the chemicals in the process system. An
upper temperature limit for using RTP dual laminates is 350°F (177°C).
The dual laminate construction lessens the problem of permeation through
liners. If there is a permeation, it is believed to pass through the RTP structure
at a rate equal to or greater than through the fluoropolymer itself, resulting
in no potential for collection of permeate at the thermoplastic-to-thermoset
interface. If delamination does not occur, permeation is not a problem.
6.2.2 Considerations in Liner Selection
Before selecting a lining material, give careful consideration to several broad
categories, specifically materials being handled, operating conditions, and
conditions external to the vessel.
The following information must be known about the materials being
handled:
1. What are the chemicals being handled and at what concentrations?
2. Are there any secondary chemicals, and if so, at what concentration?
3. Are there any trace impurities or chemicals?
4. Are there any solids present? And if so, what are their particle sizes
and concentrations?
5. If a vessel, will there be any agitation, and to what degree? If a pipeline, what are the flow rates (minimum and maximum)?
6. What are the fluid purity requirements?
The answers to the above questions will narrow the selection to those materials that are compatible. This next set of questions will narrow the selection
further by eliminating the materials that do not have the required physical
or mechanical properties.
1. What is the normal operating temperature and temperature range?
2. What peak temperatures can be reached during shutdown and
startup, process upset, etc.?
3. Will any mixing areas exist where exothermic or heat-of-mixing
temperatures can develop?
4. What is the normal operating pressure?
5. What vacuum conditions and range are possible during operation,
startup, shutdown, or upset conditions?
6. Will there be temperature cycling?
7. What cleaning methods will be used?