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Fundamentals of Corrosion
design should make maximum use of exposure to the weather. Sheltering
from rain should be avoided.
The designer should also be aware that during the period over which the
protective film is forming, rusting proceeds at a relatively high rate, during
which time rusty water is produced. This rusty water may stain masonry
pavements, and the like. Precautions should be taken to avoid detrimental
staining effects such as coloring the masonry brown so that the staining will
be obvious. The weathering steels are used primarily for bridges, buildings,
structures, and guardrails.
Plain carbon steel must have some form of protection applied to guard
the steel from corrosion. There are many options from which to choose and
these depend on the application and the severity of the atmosphere. As with
the weathering steels, sheltering should be avoided, regardless of the protective coating applied. Means of protection include painting and a variety of
metallic coatings.
11.3.2 Corrosion under insulation
A thermal insulation system consists of a thermal resistance material, a
jacket to protect the insulation and the insulated item from the local environment, and a method of attaching these materials to the object being
insulated. It may also include sealants and barriers to prevent moisture
penetration. Moisture can harm the insulation’s effectiveness and may be
the most important part of the mechanism, causing corrosion under the
insulation (CUI).
Some insulations, such as foam glass, have a structure to prevent moisture
penetration. Other insulations, such as fiberglass, must be protected by a
jacket and jacket sealant at the seams to keep out the moisture. Foam glass
inherently keeps out moisture but has characteristics that may not be suitable for all insulation situations, and it is one of the most expensive insulations. The selection table provided in this chapter shows the various factors
to be evaluated and the part played by corrosion in selecting the most suitable insulation.
11.3.2.1 Selecting a Suitable Insulation Material
Table 11.2 provides the procedure for determining a suitable insulation material. As the table shows, corrosion factors must be given consideration and
may have decisive effects on performance, safety, and economy.
There are chemical interactions to consider:
1. Insulation material can affect the metallic insulated surface. Some
insulating materials contain chlorides, or the chlorides may invade
Fundamentals of Corrosion
design should make maximum use of exposure to the weather. Sheltering
from rain should be avoided.
The designer should also be aware that during the period over which the
protective film is forming, rusting proceeds at a relatively high rate, during
which time rusty water is produced. This rusty water may stain masonry
pavements, and the like. Precautions should be taken to avoid detrimental
staining effects such as coloring the masonry brown so that the staining will
be obvious. The weathering steels are used primarily for bridges, buildings,
structures, and guardrails.
Plain carbon steel must have some form of protection applied to guard
the steel from corrosion. There are many options from which to choose and
these depend on the application and the severity of the atmosphere. As with
the weathering steels, sheltering should be avoided, regardless of the protective coating applied. Means of protection include painting and a variety of
metallic coatings.
11.3.2 Corrosion under insulation
A thermal insulation system consists of a thermal resistance material, a
jacket to protect the insulation and the insulated item from the local environment, and a method of attaching these materials to the object being
insulated. It may also include sealants and barriers to prevent moisture
penetration. Moisture can harm the insulation’s effectiveness and may be
the most important part of the mechanism, causing corrosion under the
insulation (CUI).
Some insulations, such as foam glass, have a structure to prevent moisture
penetration. Other insulations, such as fiberglass, must be protected by a
jacket and jacket sealant at the seams to keep out the moisture. Foam glass
inherently keeps out moisture but has characteristics that may not be suitable for all insulation situations, and it is one of the most expensive insulations. The selection table provided in this chapter shows the various factors
to be evaluated and the part played by corrosion in selecting the most suitable insulation.
11.3.2.1 Selecting a Suitable Insulation Material
Table 11.2 provides the procedure for determining a suitable insulation material. As the table shows, corrosion factors must be given consideration and
may have decisive effects on performance, safety, and economy.
There are chemical interactions to consider:
1. Insulation material can affect the metallic insulated surface. Some
insulating materials contain chlorides, or the chlorides may invade