ASTM C795

Covers — chemical (leachable-ion) requirements and preproduction stress-corrosion testing for any thermal insulation used in contact with austenitic stainless steel, limiting chlorides and requiring inhibiting ions (sodium/silicate) so it does not cause external chloride SCC.

Does NOT cover (exclusions) — the following are governed elsewhere:

• The insulation product itself (fiber, cellular glass, PIR) → ASTM C547 / C552 / C591.
• The stress-corrosion test method → ASTM C692; leachable-ion analysis → ASTM C1617.
• Heat-loss calculation → ISO 12241.

C795 is a chloride-safety overlay applied on top of the chosen insulation product for stainless service.

C795 sets minimum requirements for stainless-safe insulation:

• Leachable Chloride Limit — controlled maximum chloride to avoid ESCC.
• Inhibiting Ions — required sodium and silicate to counteract residual chlorides.
• Preproduction Testing — stress-corrosion test (per C692) and leachable-ion analysis (per C1617).
• Quality Control — ongoing chemistry verification of production insulation.

ASTM C795 is the chloride-safety requirement for any thermal insulation applied to austenitic stainless steel. It is not an insulation product but an acceptance standard: it limits leachable chlorides and mandates inhibiting sodium/silicate so the insulation cannot trigger external chloride stress-corrosion cracking (ESCC) — a leading cause of stainless piping failures under insulation.

Compliance is demonstrated by the stress-corrosion test of C692 and the leachable-ion analysis of C1617. In practice, stainless-line insulation is specified as, e.g., "C547 and C795," combining the product and the chloride-safety overlay.

Engineering Note: Never insulate austenitic stainless without confirming C795 compliance — a chloride-bearing insulation that gets wet will concentrate chlorides on the hot metal surface and can crack the pipe from the outside.