Overview
EN ISO 7539-4:1995 / ISO 7539-4:1989 - Corrosion of metals and alloys - Stress corrosion testing - Part 4 defines procedures for the preparation and use of uniaxially loaded tension specimens. The standard covers specimen design, surface preparation, fixturing and stressing methods (constant load, constant strain or increasing load/strain) for testing a wide range of product forms (sheet, plate, tube, wire, rod and fabricated joints such as welds or rivets). It is intended to be read in conjunction with ISO 7539-1 (general guidance on testing procedures).
Key topics and technical requirements
- Specimen forms and dimensions: constant cross-section specimens may be circular, square, rectangular or annular. Preferred machined specimens are typically >10 mm gauge length and ≥3.0 mm section where practicable.
- Surface preparation: final mechanical finishing followed by degreasing is recommended; target surface quality is about 1 µm RMS where achievable. Avoid machining damage, overheating and contamination.
- Notched and pre-cracked specimens: guidance on use of notches (triaxial stress states) and referral to ISO 7539-6 for pre-cracked specimens. Stress concentration factors (KT) apply when notches are used.
- Stressing methods: specimens may be loaded by constant load, constant strain or increasing load/strain. Chain-loading of specimens is allowed to reduce test machines.
- Environmental control: test environments should match intended service conditions where possible. Expose unstressed control specimens in parallel; exclude grips from corrosive media to avoid galvanic effects and crevice corrosion.
- Assessment and metrics: primary metric is time to total failure; other parameters include number and location of cracks, average crack velocity (longest crack length/time), remnant tensile strength and ductility (reduction of area). Tests often end after a fixed time and non-failed specimens must be examined for cracks.
- Special precautions: avoid chemical or electrochemical treatments that generate hydrogen on susceptible materials; ensure marking and reporting follow ISO 7539-1.
Applications and users
Who uses EN ISO 7539-4:
- Materials and corrosion engineers assessing stress corrosion cracking (SCC) susceptibility
- Test laboratories performing qualification, ranking and R&D on alloys, heat treatments and coatings
- Manufacturers of structural components, tubes, wires and welded assemblies validating service performance
- Failure analysts and quality assurance teams investigating environmental cracking
Practical uses:
- Material selection and ranking under specific corrosive environments
- Qualification of welded or fabricated joints for stress corrosion resistance
- Comparing effects of surface finish, heat treatment or protective coatings on SCC behavior
Related standards
- ISO 7539-1 (general guidance on testing procedures)
- ISO 7539 series: Parts 2 (bent-beam), 3 (U-bend), 5 (C-ring), 6 (pre-cracked), 7 (slow strain rate), 8 (welded specimens)
- ISO 6992 (tensile testing)
Keywords: EN ISO 7539-4:1995, ISO 7539-4, stress corrosion testing, uniaxially loaded tension specimens, stress corrosion cracking, specimen preparation, corrosion of metals and alloys.
