344
Fundamentals of Corrosion
Similarly, high-pressure steam lines, which typically require frequent
inspection, are subject to associated foot traffic.
2. Process contents in the equipment can deteriorate insulation. Nearly
all insulations are attacked by strong acid and alkali.
3. Moisture attack is another cause of deterioration of insulation. In cold
service, insulation can be used to maintain the jacket outer surface
at a temperature above the dew point. This prevents wetting of the
insulation, which could cause it to deteriorate and become ineffective.
It also prevents sweating and dripping, with resulting housekeeping
problems.
Section 11.3.2.4 provides specific design information for low-temperature systems.
Absorptive-type insulation materials (e.g., fiberglass, mineral wool, calcium silicate, etc.) will initiate corrosion on the underlying metal surfaces.
Alternate wet and dry cycles will produce corrosion of carbon steel and chloride stress corrosion of austenitic stainless steel. To ensure against corrosion
under insulation, nonabsorptive insulation materials should be considered.
These insulation characteristics are detailed later. Coating systems applied
before insulation can also protect the metallic surfaces.
For elevated temperature service, the vapor barrier must be sufficiently
permeable to vent moisture vapor yet resist passage of liquid water. For lowtemperature service, moisture in all forms must be excluded by an impermeable vapor barrier, and that barrier must be mechanically durable. A possible
exception to this rule is when cellular glass, which is itself relatively permeable, is the insulating material. However, in this case, the joints must be
sealed with the right barrier using appropriate procedures.
11.3.2.2 Design Characteristics of Insulation
The selection table guides the user through the decision-making process.
The properties that influence the insulation’s ability to resist corrosion are
moisture absorption and compressability. These properties are given for the
different types of commercial insulation. As these are typical values, manufacturers are advised to provide such ratings for the latest developments in
their products.
Abbreviations used in the text discussion to identify properties of insulations are as follows:
CaSi
Calcium silicate
ExPe
Expanded perlite
GlFi
Glass fiber
MiFi
Mineral fiber or wool
Fundamentals of Corrosion
Similarly, high-pressure steam lines, which typically require frequent
inspection, are subject to associated foot traffic.
2. Process contents in the equipment can deteriorate insulation. Nearly
all insulations are attacked by strong acid and alkali.
3. Moisture attack is another cause of deterioration of insulation. In cold
service, insulation can be used to maintain the jacket outer surface
at a temperature above the dew point. This prevents wetting of the
insulation, which could cause it to deteriorate and become ineffective.
It also prevents sweating and dripping, with resulting housekeeping
problems.
Section 11.3.2.4 provides specific design information for low-temperature systems.
Absorptive-type insulation materials (e.g., fiberglass, mineral wool, calcium silicate, etc.) will initiate corrosion on the underlying metal surfaces.
Alternate wet and dry cycles will produce corrosion of carbon steel and chloride stress corrosion of austenitic stainless steel. To ensure against corrosion
under insulation, nonabsorptive insulation materials should be considered.
These insulation characteristics are detailed later. Coating systems applied
before insulation can also protect the metallic surfaces.
For elevated temperature service, the vapor barrier must be sufficiently
permeable to vent moisture vapor yet resist passage of liquid water. For lowtemperature service, moisture in all forms must be excluded by an impermeable vapor barrier, and that barrier must be mechanically durable. A possible
exception to this rule is when cellular glass, which is itself relatively permeable, is the insulating material. However, in this case, the joints must be
sealed with the right barrier using appropriate procedures.
11.3.2.2 Design Characteristics of Insulation
The selection table guides the user through the decision-making process.
The properties that influence the insulation’s ability to resist corrosion are
moisture absorption and compressability. These properties are given for the
different types of commercial insulation. As these are typical values, manufacturers are advised to provide such ratings for the latest developments in
their products.
Abbreviations used in the text discussion to identify properties of insulations are as follows:
CaSi
Calcium silicate
ExPe
Expanded perlite
GlFi
Glass fiber
MiFi
Mineral fiber or wool