Overview
ISO 23668:2022 - Ships and marine technology - Marine environment protection - Continuous on‑board pH monitoring method - specifies performance requirements, test procedures, calibration and maintenance methods for pH meters designed for continuous on‑board monitoring using pH combination electrodes. The standard applies to measuring pH in natural seawater and freshwater, freshwater from onboard generators, and used process water (e.g., for machinery, boilers, scrubbers). It addresses practical challenges of in‑situ monitoring and supports process control and regulatory compliance for discharged water.
Key topics and technical requirements
- Scope and definitions: Defines continuous monitoring, pH value, combination electrode, slope force, transmitter, electrode mounting and cleaning device.
- pH buffer solutions: Two types - certified pH buffer solution (traceable to national/international pH standards) for manufacturer performance verification, and practical‑use buffer solution for onboard calibration. Recommended use of at least two buffers from pH 4, 7 and 9 and attention to temperature dependence.
- Performance of combination electrodes:
- Slope force requirement: confirmed to be ≥ 56.20 mV at 25 °C (verification using certified buffers).
- Other performance aspects: repeatability, linearity, stated operating pH and temperature ranges (manufacturers must provide specifications).
- Interferences and robustness: Guidance on sample conductivity, electrode fouling, electrical noise and air bubbles affecting continuous readings.
- pH meter system requirements: Covers apparatus (combination electrode, transmitter, electrode mounting), cleaning device options, mounting and placement, and reporting.
- Calibration and maintenance: Procedures for calibration using appropriate buffers, manual and automatic cleaning (including ultrasonic, mechanical, air/water methods), and electrode storage.
Applications and users
- Primary applications: Continuous monitoring of pH in marine systems - exhaust gas cleaning systems (scrubbers), boiler water, ballast or process streams, freshwater production units, and general onboard water quality monitoring.
- Intended users: Shipowners and operators, marine engineers, equipment manufacturers and integrators (pH meters, scrubbers, freshwater generators), environmental compliance officers, shipyards, and classification societies responsible for ensuring measurement reliability and discharge compliance (see IMO Resolution MEPC.340(77) context).
Related standards
- ASTM D6569-14 - Standard Test Method for On‑Line Measurement of pH
- IEC 60746-2:2003 - Expression of Performance of Electrochemical Analyzers - Part 2 - pH value
ISO 23668:2022 provides a practical, performance‑oriented framework for selecting, verifying and maintaining continuous pH monitoring systems on ships, helping ensure accurate pH control, reliable process operation and regulatory compliance for marine discharges.
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