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6
Corrosion of Linings
On many occasions, lining, coating, and paint terminologies are used interchangeably. Technically, linings and paints are both coatings. Usually, a coating is referred to as a lining when subjected to immersion, such as the interior
of a vessel, and paints refer to protective materials used to guard against
atmospheric corrosion. This chapter deals with coatings that are used to protect the interior of a vessel and will be subject to immersion.
Of the various coating applications, the most critical is that of a tank lining
application. The material must be resistant to the corrodent and be free of
pinholes through which corrosives might penetrate and reach the substrate.
The severe attack that many corrosives have on the bare tank emphasizes
the importance of using the correct material and the correct procedure in
lining a tank to obtain a perfect coating. It is also essential that the tank be
designed and constructed in the proper manner to permit the application of
a perfect lining.
In a tank lining there are usually four areas of contact with the stored
product that may lead to different types of corrosion. These areas are the
vapor phase (the area above the liquid level), the interphase (the area where
the vapor phase meets the liquid phase), the area always immersed, and the
bottom of the tank (where moisture and other contaminents of greater density may settle). Each of these areas can, at one time or another, be more
severely attacked than the rest, depending on the type of material contained,
the impurities present, and the amounts of oxygen and water present. In
view of this, it is necessary to understand the corrosion resistance of the coating material under consideration, and not just the immersed condition.
Other factors that have an effect on the performance of the coating material are vessel design, vessel, preparation prior to coating, application techniques of the coating material, curing of the coating, inspection, operating
instructions, and temperature limitations. In general, the criteria for tank
linings are:
1. Design of the vessel
2. Lining selection
3. Shell construction
4. Shell preparation
5. Lining application
6. Cure of the lining material
6
Corrosion of Linings
On many occasions, lining, coating, and paint terminologies are used interchangeably. Technically, linings and paints are both coatings. Usually, a coating is referred to as a lining when subjected to immersion, such as the interior
of a vessel, and paints refer to protective materials used to guard against
atmospheric corrosion. This chapter deals with coatings that are used to protect the interior of a vessel and will be subject to immersion.
Of the various coating applications, the most critical is that of a tank lining
application. The material must be resistant to the corrodent and be free of
pinholes through which corrosives might penetrate and reach the substrate.
The severe attack that many corrosives have on the bare tank emphasizes
the importance of using the correct material and the correct procedure in
lining a tank to obtain a perfect coating. It is also essential that the tank be
designed and constructed in the proper manner to permit the application of
a perfect lining.
In a tank lining there are usually four areas of contact with the stored
product that may lead to different types of corrosion. These areas are the
vapor phase (the area above the liquid level), the interphase (the area where
the vapor phase meets the liquid phase), the area always immersed, and the
bottom of the tank (where moisture and other contaminents of greater density may settle). Each of these areas can, at one time or another, be more
severely attacked than the rest, depending on the type of material contained,
the impurities present, and the amounts of oxygen and water present. In
view of this, it is necessary to understand the corrosion resistance of the coating material under consideration, and not just the immersed condition.
Other factors that have an effect on the performance of the coating material are vessel design, vessel, preparation prior to coating, application techniques of the coating material, curing of the coating, inspection, operating
instructions, and temperature limitations. In general, the criteria for tank
linings are:
1. Design of the vessel
2. Lining selection
3. Shell construction
4. Shell preparation
5. Lining application
6. Cure of the lining material