ISO 18070:2015

Overview

ISO 18070:2015 - "Corrosion of metals and alloys - Crevice corrosion formers with disc springs for flat specimens or tubes made from stainless steel" specifies a standardized crevice-forming technique and hardware (crevice former) for laboratory crevice corrosion testing of stainless-steel flat specimens and tubes in corrosive solutions. The document defines the mechanical assembly, materials, specimen geometry and surface preparation of the crevice former and associated disc-spring loading system. It does not prescribe how to carry out the corrosion test procedure or how to evaluate attack - only the crevice former design and handling.

Key topics and technical requirements

• Crevice former design: PVDF crevice formers (OD 20 mm, ID 7 mm, height 15 mm) for flat specimens; tubular formers include a curvature matching the tube OD and minimum thickness 5 mm. PVDF usable to ~95 °C.
• Loading system: Disc springs (Belleville washers) with a calibrated linear force–deflection relationship (reference DIN 2093). Typical assembly uses four springs to achieve ~0.9 kN (~3 Nm torque for flat specimens).
• Assembly components & materials: Nut, bolt and washers (rings) typically made from titanium; disc springs made from titanium or nylon-coated steel. Insulating PVC/PE hose and PTFE centering rings prevent electrical contact and align parts.
• Specimen requirements: Minimum outer surface area ≥ 100 cm²; flat specimens and tubes require a central 7 mm hole; tubes at least 30 mm long.
• Surface preparation & cleanliness: Test surfaces normally abraded to at least P120 grit (ISO 6344-3); crevice formers wet-ground to at least P1200. Clean specimens with degreasing, high-purity water (conductivity < 1 µS/cm per ISO 3696) and solvent; allow 24 h in air above dew point to form stable oxide before testing.
• Calibration & documentation: Measure washer spacing before and after loading (LBL, LAL) and calculate deflection (ΔL). Use torque wrenches and verify deflection within calibration tolerances. Annex gives example test-report format.

Practical applications and users

• Useful for corrosion labs, materials scientists, and quality/engineering teams needing reproducible crevice corrosion testing of stainless steels.
• Valuable for R&D, failure analysis, alloy selection, and screening of materials and surface finishes for marine, chemical processing, and other corrosive environments.
• Enables integration with electrochemical measurements when specimens are configured for electrical connections.

Related standards

• ISO 3696 - Water for analytical laboratory use
• ISO 8044 - Corrosion basic terms and definitions
• ISO 6344-3 - Coated abrasives grain size
• DIN 2093 - Disc spring dimensions/quality

Keywords: ISO 18070:2015, crevice corrosion, crevice former, disc springs, stainless steel testing, PVDF, Belleville washers, crevice corrosion testing.