ISO 7539-4:1989

ISO 7539-4:1989 - Overview

ISO 7539-4:1989 is part of the ISO 7539 series on Corrosion of metals and alloys - Stress corrosion testing. This part specifies procedures for the design, preparation and use of uniaxially loaded tension specimens to evaluate susceptibility to stress corrosion. It covers specimen forms (sheet, plate, tube, wire, rod and fabricated/joined parts), stressing methods (constant load, constant strain or increasing load/strain) and guidance for interpreting results in conjunction with ISO 7539-1.

Key topics and technical requirements

• Specimen types and geometry
  • Constant cross-section specimens (circular, square, rectangular, annular) or tapered gauge lengths; notched and pre-cracked variants allowed.
  • Transition radii and avoidance of sharp corners to reduce stress concentrations.
  • Small cross-sections increase sensitivity but are harder to machine and more variable.
• Surface preparation
  • Mechanical finishing followed by degreasing is preferred unless as-supplied surfaces are under study.
  • Aim for surface quality around 1 µm RMS where practicable.
  • Avoid overheating, excessive pressure, contamination and hydrogen-producing treatments for susceptible materials.
  • Electropolishing may help but is not guaranteed to remove preparation artifacts.
• Grips and fixture considerations
  • Gripped ends may be any shape that suits holders but should ideally be excluded from the corrosive environment to prevent galvanic or crevice effects.
  • Chains of specimens may be used to reduce equipment needs.
• Test procedure and environment
  • Stressing may be applied before or after exposure to the test environment; exposure timing should match intended service conditions when possible.
  • Use unstressed controls under identical exposure to isolate the effect of applied stress.
  • Binary search can be used to determine threshold stress with fewer specimens.
• Assessment and reporting
  • Primary parameter: time to total failure. Also report number/location of cracks, average crack velocity (longest crack length / test time), remnant strength and ductility measures.
  • Examine specimens that did not fail for cracks (metallography may reveal small cracks).
  • Test report should include material description, specimen details and surface prep, stressing procedure, environment and exposure time, and assessment methods.

Applications and users

• Intended for corrosion engineers, materials testing laboratories, R&D teams, and quality assurance groups needing standardized stress corrosion testing using tensile specimens.
• Applicable when evaluating new alloys, product forms (sheet, rod, tube), welded or joined parts, and when comparing susceptibility across environments or manufacturing conditions.

Related standards

• ISO 7539-1: General guidance on testing procedures
• Other parts of ISO 7539 series (Parts 2–8 cover bent-beam, U-bend, C-ring, pre-cracked, slow strain rate, welded specimens)
• ISO 6992: Metallic materials - Tensile testing

Keywords: ISO 7539-4, stress corrosion testing, uniaxially loaded tension specimens, tensile specimens, specimen preparation, stress corrosion cracking, corrosion testing.