Protection against Corrosion under insulation

Prevention, Identification, and protection against corrosion

Highly alloyed austenitic steels (alloys of chrome, nickel and molybdenum) are predisposed to tensile stress corrosion (stress corrosion cracking), caused mainly by water soluble ions, such as chlorides. As temperature increases, so does the risk of stress corrosion cracking. All KIMMCO-ISOVER industrial products are therefore low in chlorides.

Moisture and water repellence

Low chloride insulation products are the basis for preventing corrosion under insulation (CUI), especially where higher temperature surfaces are involved. In addition, all KIMMCO-ISOVER industrial insulation products for external use are hydrophobic and non-hygroscopic, thus limiting potential water absorption. The open cell structure allows products to dry out quickly, should they become wet, without loss of their mechanical or insulating properties. Hydrophobic performance is tested and measured according to AGI-Q 132, which allows for water absorbtion of less than 1kg/m² after 24 hours. Nevertheless mineral wool products should always be stored inside and in dry conditions, in order to maintain their performance and low chloride content, When used for outdoor applications or on cold surfaces, metal sheet jacketing or equivalent vapour barriers should always be used.

Standards and guidelines

There are different standards to define the limits for water-leachable ions in insulation products:

  • ASTM C 795, for instance, concerns the water-leachable content of chloride, sodium and silicate ion's.
  • The so-called Karnes diagram defines an acceptable area which is identified as not supporting stress corrosion. All ISOVER industrial solutions fall within the acceptable area.
  • AS-Quality (AGI-Q 132): even more demanding is the AGI-Q 132 which sets the maximum content of chloride ions at 10ppm or 10mg per 1 kg of insulation material. Insulation materials which satisfy this standard are certified for AS-Quality. Austenitic (AS) is a term which describes a particular type of crystalline steel structure. ISOVER has certified nearly all of its products for high-temperature usage as AS-Quality - giving additional safety to highly demanding constructions.

Acceptable analysis of water-leachable ions in mineral wool according to Karnes diagram