Roxul Industrial Insulation Process - Manual (Page 118)

2.2.4 Water leachable chloride content
The corrosion resistance of steel is increased by
the addition of alloying elements such as
chromium, nickel and molybdenum. Since this
alloying results in a so-called austenitic (face-
centred cubic) atomic structure, these types of
steel are also called austenitic steels.
Despite their generally high resistance to
corrosion, these steels tend to exhibit stress
corrosion under certain conditions. Three
boundary conditions must all be fulfilled in order
for stress corrosion cracking to occur:
The material must be susceptible to stress
corrosion.
Tensile stresses must be present in the
component (for example, as a result of thermal
elongations).
There must be a specific attacking agent.
These specific attacking agents include, for
example, chloride ions. An insulation material
with an extremely low quantity of water-leachable
chlorides must therefore be used to insulate
objects made from austenitic stainless steel.
For this application, only those insulation
materials that are manufactured with a low water
leachable chloride content may be used. The
classification criteria will depend on the used
standard. In general, a distinction can be made
between American ASTM standards and European
EN standards.
ASTM C871
“Standard Test Methods for Chemical Analysis of
Thermal Insulation Materials for Leachable
Chloride, Fluoride, Silicate, and Sodium Ions”.
This standard covers the laboratory procedures
for the determination of the mentioned ions which
accelerate stress corrosion of stainless steel. If
the results of the chemical analysis for the
leachable ions chloride, sodium and silicate fall in
the acceptable area of the graph in ASTM C795
and also pass ASTM C692, the insulation material
should not cause stress corrosion cracking.
ASTM C692
“Standard Test Method for Evaluating the
Influence of Thermal Insulations on External
Stress Corrosion Cracking Tendency of Austenitic
Stainless Steel”.
This standard covers the procedures for the
laboratory evaluation of thermal insulation
materials that may actively contribute to external
stress corrosion cracking (ESCC) of austenitic
stainless steel due to soluble chlorides within the
insulation. This corrosion test consists of using
specimens of insulation to conduct distilled or
deionized water by wicking or dripping to an
outside surface, through the insulation, to a hot
inner surface of stressed stainless steel for a
period of 28 days. If leachable chlorides are
present, they will concentrate on the hot surface
by evaporation. At the conclusion of the 28-day
test period, the stainless steel coupons are
removed, cleaned and inspected for stress
corrosion cracks. To pass the test no cracks may
be found on the surface of the coupons.
AS-Quality (AGI Q135 – EN 13468)
The following acceptance criteria apply for
insulation materials of AS-Quality. The average of
six test samples must exhibit a water leachable
chloride content of ≤ 10ppm (10 mg/kg) The
maximum value of individual measurements must
not exceed 12 ppm (12 mg/kg).
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