184
Fundamentals of Corrosion
As with any material, the corrosion resistance, allowable operating values,
and cost vary with each. Care must be taken when selecting the lining material so that it is compatible with the corrodent being handled at the operating
temperatures and pressures required.
6.2.1 Shell Design
The design of the vessel shell is critical if the lining is to perform satisfactorily. For the lining to be installed properly, the vessel must meet certain
design configurations. Although these details may vary slightly depending
upon the specific lining material used, there are certain design principles
that apply in all cases:
1. The vessel must be of butt-welded construction.
2. All internal welds must be ground smooth.
3. All weld spatter must be removed.
4. All sharp corners must be ground to a minimum of 1/8-in. radius.
5. All outlets must be of flanged or pad type. Certain lining materials
require that nozzles be not less than 2 in. (51 mm) in diameter.
6. No protrusions are permitted inside the vessel.
Once the lining has been installed, there should be no welding permitted on
the exterior of the vessel.
After completing the fabrication, the interior surface of the vessel must
be prepared to accept the lining. This is a very critical step. Unless the
surface is properly prepared, proper bonding of the lining to the shell
will not be achieved. The basic requirement is that the surface be absolutely clean. To ensure proper bonding, all surfaces to be lined should
be abrasive-blasted to white metal, in accordance with SSPC specification Tp5–63 or NACE specification 1. A white metal surface condition is
defined as being one where all rust, paint, scales, and the like have been
removed and the surface has a uniform gray-white appearance. Streaks or
stains of rust or other contaminents are not allowed. A near-white, blastcleaned finish equal to SSPC SP 10 is allowed on occasion. This is a more
economical finish. In any case, it is essential that the finish be as the lining
contractor has specified. Some lining contractors will fabricate the vessel
as well as prepare the surface. When the total responsibility is placed on
the lining contractor, the problem is simplified, and a better product will
usually result.
When a vessel shell is fabricated from a reinforced thermosetting plastic
(RTP), several advantages are realized. The RTPs generally have a wider range
of corrosion resistance, but relatively low allowable operating temperatures.
When a fluoropolymer-type lining is applied to an RTP shell, the temperature
Fundamentals of Corrosion
As with any material, the corrosion resistance, allowable operating values,
and cost vary with each. Care must be taken when selecting the lining material so that it is compatible with the corrodent being handled at the operating
temperatures and pressures required.
6.2.1 Shell Design
The design of the vessel shell is critical if the lining is to perform satisfactorily. For the lining to be installed properly, the vessel must meet certain
design configurations. Although these details may vary slightly depending
upon the specific lining material used, there are certain design principles
that apply in all cases:
1. The vessel must be of butt-welded construction.
2. All internal welds must be ground smooth.
3. All weld spatter must be removed.
4. All sharp corners must be ground to a minimum of 1/8-in. radius.
5. All outlets must be of flanged or pad type. Certain lining materials
require that nozzles be not less than 2 in. (51 mm) in diameter.
6. No protrusions are permitted inside the vessel.
Once the lining has been installed, there should be no welding permitted on
the exterior of the vessel.
After completing the fabrication, the interior surface of the vessel must
be prepared to accept the lining. This is a very critical step. Unless the
surface is properly prepared, proper bonding of the lining to the shell
will not be achieved. The basic requirement is that the surface be absolutely clean. To ensure proper bonding, all surfaces to be lined should
be abrasive-blasted to white metal, in accordance with SSPC specification Tp5–63 or NACE specification 1. A white metal surface condition is
defined as being one where all rust, paint, scales, and the like have been
removed and the surface has a uniform gray-white appearance. Streaks or
stains of rust or other contaminents are not allowed. A near-white, blastcleaned finish equal to SSPC SP 10 is allowed on occasion. This is a more
economical finish. In any case, it is essential that the finish be as the lining
contractor has specified. Some lining contractors will fabricate the vessel
as well as prepare the surface. When the total responsibility is placed on
the lining contractor, the problem is simplified, and a better product will
usually result.
When a vessel shell is fabricated from a reinforced thermosetting plastic
(RTP), several advantages are realized. The RTPs generally have a wider range
of corrosion resistance, but relatively low allowable operating temperatures.
When a fluoropolymer-type lining is applied to an RTP shell, the temperature