"Corrosion under insulation is a very serious issue.
...
The most common corrosive ion is the chloride ion, which can be introduced through wash down water, brine, sea water, potable water or cleaning solutions. It can also originate from a range of other sources, including the insulation itself. Installations in coastal areas subject to salt water, heat, and high humidity are particularly prone to corrosion issues.
Almost all insulation products contain chloride ions. Even non-wicking thermal insulations can trap and hold chloride ions against the stainless steel surface. Fortunately, there are several specifications for corrosion control requirements.
Testing Insulations For Corrosive Properties
Three standards have evolved as the primary test methods to address stress corrosion of austenitic stainless steel:
•
ASTM C795 Standard Specification for Thermal Insulation for Use in Contact with Austenitic Stainless Steel.
• MIL-I-24244 Insulation Material, with Special Corrosion, Chloride, and Fluoride Requirements. U.S. Department of Defense specification for nuclear propulsion systems.
•
NRC 1.36 - Regulatory Guide for Nonmetallic Thermal Insulation for Austenitic Stainless Steel. Specification
developed by the U.S. Nuclear Regulatory Commission for the nuclear power industry.
These similar standards specify chemical properties of insulation intended for use in contact with stainless steel to minimize the possibility of stress corrosion. They quantify the maximum chloride ions permissible, as well as the minimum ratio of sodium and silicate to chloride ions.
...
A practical method of reducing potential for stress corrosion is to use an insulation such as T-12 or WR-1200, which are manufactured with sodium silicate. The basic chemistry of these industrial insulations neutralizes chlorides. IIG MinWool 1200 Pipe and Board insulation also effectively minimize corrosion potential.
Corrosion Resistant Paint
In areas of high stress corrosion potential, a recommended industry practice is to apply a protective paint or specialty coating to stainless steel prior to insulating. An industrial insulation supplier can provide appropriate materials."
Info above from the following insulation supplier:
Additional links:
ASTM C692-06, 'Standard Test Method for Evaluating the Influence of Thermal Insulations on External Stress Corrosion Cracking Tendency of Austenitic Stainless Steel.'
ASTM C795 (cited above)
ASTM C1617-05, 'Standard Practice for Quantitative Accelerated Laboratory Evaluation of Extraction Solutions Containing Ions Leached from Thermal Insulation on Aqueous Corrosion of Metals.'
ASTM STP 880, 'Corrosion of Metals Under Thermal Insulation' Article titles & abstracts are available for free; the entire book or individual articles can be ourchased:
MIL-I-24244 (cited above), now MIL-DTL-24244D:
"This specification covers asbestos-free thermal insulation, cement and adhesives, all with special corrosion, chloride and fluoride requirements"
So crucial to US security that it's a 'Controlled Distribution Document.'
'New Industry Standards, Test Procedures and Surface Treatments Combat Corrosion Under Insulation (NACE)'
