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Materials of Construction - Acid Resistant Linings
May 9, 2003
Introduction
Sulphuric acid is a highly corrosive and
equipment design to handle sulphuric must be corrosion resistant. Exotic alloys are
available which provide excellent corrosion resistance and long service life. The
disadvantages of these alloys are their high costs. Acid resistant linings have been
used since the early days of sulphuric acid manufacture. They provide excellent
resistance to sulphuric acid at a reasonable cost since less expensive materials such as
carbon steel can be used for the walls of the vessel or tank.
Traditional lining materials are:
These materials are commonly used in
combination with each other to provide the total acid resistant lining for protection of
carbon steel vessels.
Pecora Mastic and Acid Resistant Brick
| Description |
This lining system consist of a thin layer (3
mm) of pecora mastic which is trowelled on to the steel surface. The steel surface
must be free of mill scale, rust, dirt, etc. Generally, the surface of the steel is
sandblasted or wire brushed. A layer of mortar (5 mm) is applied directly over the
pecora mastic and the first layer of acid resistant brick is set into the mortar. |
| Advantages |
- Relatively low first cost
- Ease of application
- Effective unless damaged by excessive temperatures
- Life expectancy of approximately 20 years
|
| Disadvantages |
- Low threshold temperature
- Ineffective if not applied over the entire surface of the
steel being bricklined
|
Pecora Mastic, PTFE and Acid Resistant Brick
| Description |
This lining system consist of a thin layer (3
mm) of pecora mastic which is trowelled on to the steel surface. The steel surface
must be free of mill scale, rust, dirt, etc. Generally, the surface of the steel is
sandblasted or wire brushed. 10 mil PTFE sheets are laid on top of the pecora mastic
while it is still tacky. The pecora mastic is used to hold the PTFE sheet in place
as well as providing an added layer of protection. The PTFE sheets are overlapped a
minimum of 150 mm (6”). A layer of mortar (5 mm) is applied directly over the
PTFE sheet and the first layer of acid resistant brick is set into the mortar. |
| Advantages |
- PTFE sheets are impervious to sulphuric acid
- Life expectancy of more than 20 years
|
| Disadvantages |
- Higher incremental cost than pecora mastic and acid resistant
brick
- PTFE sheets to not stick well to the pecora mastic
- Higher cost for installation
- Longer to install
- If PTFE sheet is punctured, acid may pool behind the PTFE
sheet
|
PTFE and Acid Resistant Brick
| Description |
This lining system consists of 10 mil PTFE
sheets applied to the steel sheel using an epoxy. The steel surface must be free of
mill scale, rust, dirt, etc. Generally, the surface of the steel is
sandblasted. The PTFE sheets are overlapped a minimum of 150 mm (6”). A
layer of mortar (5 mm) is applied directly over the PTFE sheet and the first layer of acid
resistant brick is set into the mortar. |
| Advantages |
- PTFE sheets are impervious to sulphuric acid
|
| Disadvantages |
- Requires an excellent surface preparation to ensure complete
adhesion of the PTFE sheets
- The epoxy has a low temperature limit and will fail over time
|
Ceramic Paper
Ceramic paper soaked in potassium silicate is generally used in 'dry' service
only. It is therefore not suitable as a lining for towers or pumptanks.
However, ceramic paper soak in potassium silicate is used in areas that are normally hot
and there is the risk that the acid dew point is reached during normal operation or during
shutdowns. Areas of application are sulphur furnaces where the ceramic paper is
installed between the refractory lining and carbon steel shell or on refractory lined hot
gas ducts.
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