ASTM C871-04

It has been demonstrated that chlorides, when deposited and concentrated on the surface of austenitic stainless steel, can contribute to external stress corrosion cracking (ESCC).⁵ Analysis for fluoride has been covered because Test Methods C 871 is the “source document” for other standards that require testing for leachable fluoride ions.

Testing⁶ has shown that, using the methodology of Test Method C 692, neither fluoride nor iodide nor bromide initiates ESCC in the manner that can be demonstrated with chloride. After being exposed to 1500 mg/kg fluoride for 60 days with no cracking, a change to 1500 mg/kg chloride resulted in cracking in 3 days, as required by the metal qualification procedure in Test Method C 692. Similar tests with iodide and bromide showed that these ions do not promote ESCC as does chloride.

Chlorides (and fluorides) can be constituents of the insulating material or of the environment, or both. Moisture in the insulation or from the environment can cause chlorides (and fluorides) to migrate through the insulation and concentrate at the hot stainless steel surface.

The presence of sodium and silicate ions in the insulation has been found to inhibit external stress corrosion cracking caused by chloride (and fluoride) ions, whether such ions come from the insulation itself or from external sources. Furthermore, if the ratio of sodium and silicate ions to chloride (and fluoride) ions is in a certain proportion in the insulation, external stress corrosion cracking as a result of the presence of chloride (and fluoride) in the insulation will be prevented or at least mitigated (see also Specification C 795).

1.1 These test methods cover laboratory procedures for the determination of water-leachable chloride, fluoride, silicate, and sodium ions in thermal insulation materials in the parts per million range.

1.2 Selection of one of the test methods listed for each of the ionic determinations required shall be made on the basis of laboratory capability and availability of the required equipment and appropriateness to the concentration of the ion in the extraction solution.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.