186
Fundamentals of Corrosion
Finally, consideration must be given to conditions external to the vessel or
pipe:
1. What are the ambient temperature conditions?
2. What is the maximum surface temperature during operation?
3. What are the insulation requirements?
4. What is the nature of the external environment? This can dictate finish requirements and/or affect the selection of the shell material.
5. What are the external heating requirements?
6. Is grounding necessary?
Armed with the answers to these questions, an appropriate selection of liner
and shell can be made.
6.2.2.1 Bonded Linings
Bonded linings have several advantages over loose or unbonded linings,
including:
1. They have superior performance in vacuum service, resisting collapse to full vacuum if designed properly.
2. During thermal or pressure cycling, bonded linings follow the
movement of the structural wall, avoiding stress concentrations at
nozzles and other anchor points.
3. There is less permeation for bonded linings than for unbonded
linings because permeate must pass through the liner and the
substrate.
The construction of adhesive bonded sheet linings on steel substrate consists
of fabric-backed sheets bonded to steel vessel walls with neoprene- or epoxybased adhesive. Liners may be installed in the field or in the shop.
To protect the liner from delamination, a differential expansion or buffer layer is used. This is the bonding layer between the vessel wall and the
fabric backing of the liner. Delamination is due primarily to the difference in
expansion rates between the structural wall and the lining.
The linear coefficient of a liner free to move would typically be approximately twice that of the structural wall. In any case, the relative stresses set
up by the differential expansion of the materials must be determined and the
allowable physical properties must not be exceeded.
For process applications that require a lining that will resist harsh chemicals, usually one of the fluoropolymers is selected. Because these linings are
expensive, representing 80% of the cost of the vessel, a fabricator must be
Fundamentals of Corrosion
Finally, consideration must be given to conditions external to the vessel or
pipe:
1. What are the ambient temperature conditions?
2. What is the maximum surface temperature during operation?
3. What are the insulation requirements?
4. What is the nature of the external environment? This can dictate finish requirements and/or affect the selection of the shell material.
5. What are the external heating requirements?
6. Is grounding necessary?
Armed with the answers to these questions, an appropriate selection of liner
and shell can be made.
6.2.2.1 Bonded Linings
Bonded linings have several advantages over loose or unbonded linings,
including:
1. They have superior performance in vacuum service, resisting collapse to full vacuum if designed properly.
2. During thermal or pressure cycling, bonded linings follow the
movement of the structural wall, avoiding stress concentrations at
nozzles and other anchor points.
3. There is less permeation for bonded linings than for unbonded
linings because permeate must pass through the liner and the
substrate.
The construction of adhesive bonded sheet linings on steel substrate consists
of fabric-backed sheets bonded to steel vessel walls with neoprene- or epoxybased adhesive. Liners may be installed in the field or in the shop.
To protect the liner from delamination, a differential expansion or buffer layer is used. This is the bonding layer between the vessel wall and the
fabric backing of the liner. Delamination is due primarily to the difference in
expansion rates between the structural wall and the lining.
The linear coefficient of a liner free to move would typically be approximately twice that of the structural wall. In any case, the relative stresses set
up by the differential expansion of the materials must be determined and the
allowable physical properties must not be exceeded.
For process applications that require a lining that will resist harsh chemicals, usually one of the fluoropolymers is selected. Because these linings are
expensive, representing 80% of the cost of the vessel, a fabricator must be