Overview
EN ISO 12732:2008 (ISO 12732:2006) defines the Double Loop Electrochemical Potentiokinetic Reactivation (DL‑EPR) test, based on Čihal’s method, for measuring the degree of sensitization (DOS) in stainless steel and nickel‑based alloys. The standard specifies the DL‑EPR test principle, apparatus, test solutions, specimen preparation, procedure, evaluation and reporting. Results provide a quantitative index of alloy‑element depletion at grain boundaries or in the matrix and indicate potential susceptibility to localized corrosion modes, while noting that complementary tests are required for definitive prediction.
Key topics and technical requirements
- Test principle: DL‑EPR uses a double polarization loop - activation/passivation followed by a cathodic reactivation scan - to generate activation and reactivation peaks and integrated charges (Q and Qr). Ratios of peak currents or charges relative to solution‑annealed references are used to quantify DOS.
- Sensitization detection: Sensitive to chromium (or other alloying element) depleted zones that lower local passivity and promote localized dissolution during the reactivation scan.
- Apparatus requirements:
- Scanning potentiostat capable of controlling potential to ±1 mV.
- Potential range approximately −2000 to +2000 mV and current range 1 µA to 1 A (as indicated in the standard).
- Reference electrode circuit with high input impedance to avoid measurement errors.
- Symmetric counter‑electrode arrangement and chemically inert test cell materials (e.g., borosilicate glass, PTFE).
- Specimen considerations: Surface preparation impact is reduced by the double‑loop method, but special care is required for heat‑affected zones (HAZ) of welds because sensitized regions may be non‑uniform.
- Data evaluation: Use peak currents and integrated charges, normalize for grain size when required, and confirm localized corrosion by metallographic inspection.
Applications and users
- Practical uses:
- Rapid screening for degree of sensitization after heat treatment or welding.
- Assessment of susceptibility to intergranular corrosion, pitting, and intergranular stress corrosion cracking (as an index-complementary testing needed for full assessment).
- Quality control in heat‑treatment, welding qualification, failure analysis, and alloy selection.
- Typical users:
- Corrosion engineers, metallurgists, NDT specialists, welding engineers, research laboratories, and materials qualification teams working with stainless steels and nickel alloys.
- Manufacturers in chemical, petrochemical, nuclear, and offshore industries where localized corrosion resistance is critical.
Related standards
- ISO 8044:1999 - Corrosion of metals and alloys - Basic terms and definitions.
- ISO 643:2003 - Steels - Micrographic determination of the apparent grain size.
- EN ISO 12732:2008 includes informative annexes (e.g., recommended exposure conditions and correlations) useful for implementing DL‑EPR testing.
Keywords: EN ISO 12732:2008, DL‑EPR, Double Loop Electrochemical Potentiokinetic Reactivation, degree of sensitization, stainless steel, nickel‑based alloys, electrochemical testing, corrosion susceptibility.