ASTM C692

Applies to: Qualification testing of thermal insulation materials (calcium silicate, mineral wool, perlite, fiberglass, cellular glass) for potential to cause external SCC of austenitic stainless steel (300-series) pipe operating above ~60 °C; a required test for compliance with ASTM C795.

Does NOT cover: Carbon steel or duplex stainless CUI evaluation; installation or system design requirements; mechanical properties of insulation materials.

• Immersion of stressed austenitic stainless steel test specimens in aqueous insulation extract
• Test temperature 96 °C for 336-hour duration
• Specimen visual and microscopic examination for cracks
• Pass/fail determination: no SCC cracking = pass
• Test required for any new or reformulated insulation product intended for 300-series stainless service

ASTM C692 addresses the CUI-SCC mechanism: chloride-containing insulation leaching onto hot austenitic stainless steel under residual or operating stress causes sudden external stress-corrosion cracking. Insulation products specified for 300-series stainless piping above ~60 °C should comply with ASTM C795, which incorporates C692 testing as the SCC qualification test.

Engineering note: Engineers specifying insulation for stainless steel piping (e.g., SS process lines in ethylene or LNG plants) must verify that each insulation product has passed ASTM C692 testing and holds current ASTM C795 compliance documentation. Products that fail at elevated test temperatures or have high chloride leachate content pose CUI-SCC risk that can cause catastrophic brittle fracture without warning.