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Q: Can Johns Manville insulations be used in contact with austenetic stainless steel?
A: Insulation used in contact with austenetic stainless steel should comply with the appropriate industry standard specification. The following three insulation specifications deal with stress corrosion of stainless steel:
- ASTM C 795 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
- NRC 1:36 Stress Corrosion - Nuclear Industry
These three specifications are essentially identical. There are two sections to each specification: a corrosion test and a chemical analysis. The corrosion test must show no corrosion of a heated, stressed stainless steel coupon after 28 days of contact with insulation leachant. The chemical analysis must show that the chloride ion concentration is below the allowed maximum, and that the ratio of the concentration of sodium plus silicate ions to the concentration of chloride ions is above the allowed minimum.
The following Johns Manville Insulations comply with these standards:
- Thermo-12 Gold®
- Micro-Lok® (from Defiance only - should be indicated on PO)
- Pipe and Tank Insulation
- 800 Series Spin-Glas® (from Cleburne only - should be indicated on PO)
- 1000 Series Spin-Glas®
- Precipitator Spin-Glas®
- HTB 23 & 26 Spin-Glas®
- Super Firetemp® Boards L, M, S, T, X
Certification to these specifications is available for a fee. If certification is required it must be stated on the PO.
Chloride ions can be introduced to the system from other sources including sweat and salt water, and generally this external source is the cause of stress corrosion. The insulation is not intended to "neutralize" chlorides from other sources. Where stress corrosion is a significant concern it is 1)prudent, 2)recommended by Johns Manville, and 3)common industry practice to apply a protective paint to stainless steel prior to application of insulation to provide additional protection from corrosion. Appropriate paints are:
- For temperatures 300F and lower: epoxy phenolic such as:
- Ameron 90, Ameron, Protective Coatings Division, Brea, California
- Plasite 7122, Wisconsin Protective Coatings, Green Bay, Wisconsin
- For temperatures 750F and lower: zinc free silicone such as:
- Carboline 4674, Carboline Co, St. Louis, Missouri
- Thermolox 70, Dampney Coating Manufacturing, Everett, Massachusetts
- For temperatures up to 850F: high temperature, ambient cure silicone such as:
- UC-45732 Black High Heat Silicone, PPG Industries, Houston, Texas
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