The Equipment Design Process
353
The problem is most prevalent with plants in coastal areas and
plants producing chloride-containing chemicals. A solution to
the problem is to apply protective coatings to the metal or keep
the insulation dry. Because the latter is difficult to assure, protective coatings appear to be the additional measure to avoid the
problem.
Inorganic zinc coatings under insulation appear to accelerate
rather than inhibit the corrosion of steel. They are to be avoided
in the “wet temperature” range between 140 and 230ºF. Inorganic
zinc coatings are difficult to apply properly and are not the paint of
choice.
The epoxy/urethane system currently used for bare steel will
provide protection for insulated steel in the operating range
between –50 and 200/250ºF. An epoxy system is also a good
choice for use under insulation where the urethane topcoat is
replaced by a second epoxy coat. This system will continue to be
a good standard system for chloralkali plants and for Gulf Coast
plants for insulated and bare carbon steel.
The amine-cured coal tar and modified epoxy system is recommended for cold (−50ºF to 50ºF) and cyclic services where frequent heating and cooling will be an operating mode. In these
cases, it is worth the inconvenience of having a two-paint system
on the project.
6. As a wet environment under insulation can lead to an accumulation of chlorides and chloride stress cracking with austenitic
stainless steels, stainless steel that is insulated with a cold service cellular glass system (permeability 0 to 0.005 perm/in.) and
that will keep moisture out does not require a protective coating.
Use of other insulating materials and hot service insulating systems requires that the stainless steel receive a protective coating prior to insulation. Use either an epoxy phenolic or coal tar
epoxy. Proper preparation is essential when painting stainless
steel.
3. Cryogenic service:
This type of insulation is applied on piping and equipment
operating below the temperature range for normal cold insulation
(−100ºF to −450ºF), and a study should be done to determine if special insulation systems, for example, cold box-type or double-wall,
are economically justified. The vapor barriers and design considerations require special studies with the suppliers of cryogenic
insulation.
353
The problem is most prevalent with plants in coastal areas and
plants producing chloride-containing chemicals. A solution to
the problem is to apply protective coatings to the metal or keep
the insulation dry. Because the latter is difficult to assure, protective coatings appear to be the additional measure to avoid the
problem.
Inorganic zinc coatings under insulation appear to accelerate
rather than inhibit the corrosion of steel. They are to be avoided
in the “wet temperature” range between 140 and 230ºF. Inorganic
zinc coatings are difficult to apply properly and are not the paint of
choice.
The epoxy/urethane system currently used for bare steel will
provide protection for insulated steel in the operating range
between –50 and 200/250ºF. An epoxy system is also a good
choice for use under insulation where the urethane topcoat is
replaced by a second epoxy coat. This system will continue to be
a good standard system for chloralkali plants and for Gulf Coast
plants for insulated and bare carbon steel.
The amine-cured coal tar and modified epoxy system is recommended for cold (−50ºF to 50ºF) and cyclic services where frequent heating and cooling will be an operating mode. In these
cases, it is worth the inconvenience of having a two-paint system
on the project.
6. As a wet environment under insulation can lead to an accumulation of chlorides and chloride stress cracking with austenitic
stainless steels, stainless steel that is insulated with a cold service cellular glass system (permeability 0 to 0.005 perm/in.) and
that will keep moisture out does not require a protective coating.
Use of other insulating materials and hot service insulating systems requires that the stainless steel receive a protective coating prior to insulation. Use either an epoxy phenolic or coal tar
epoxy. Proper preparation is essential when painting stainless
steel.
3. Cryogenic service:
This type of insulation is applied on piping and equipment
operating below the temperature range for normal cold insulation
(−100ºF to −450ºF), and a study should be done to determine if special insulation systems, for example, cold box-type or double-wall,
are economically justified. The vapor barriers and design considerations require special studies with the suppliers of cryogenic
insulation.