Overview
ISO 18611-2:2014 specifies the test methods required to determine the quality characteristics of the marine NOx reduction agent AUS 40 (aqueous urea solution). Part 2 of the ISO 18611 series defines sampling, analytical procedures and precision requirements used to confirm compliance with the quality limits set out in ISO 18611-1. The standard is targeted at marine applications for selective catalytic reduction (SCR) systems and is applicable regardless of AUS 40 manufacturing method.
Key topics and technical requirements
- Scope and linkage: Test methods to verify the AUS 40 quality parameters defined in ISO 18611-1; complements ISO 18611-1 (quality requirements) and ISO 18611-3 (handling, transport, storage).
- Sampling (Annex A): Procedures for representative sampling across the supply chain, bottle materials (HDPE, HDPP, PFA, PTFE alternatives), labeling and chain-of-custody requirements, and storage guidance (preferably 1 °C to 20 °C; long-term 1 °C to 15 °C). Analysis is recommended within three weeks to account for ammonia changes.
- Analytical methods (Annexes B–J):
- Urea content by total nitrogen (combustion analysis) and by refractive index
- Density determination (ISO 3675 or ISO 12185 referenced)
- Alkalinity, biuret, aldehyde and insoluble matter test methods
- Phosphate by photometric method
- Trace elements (Ca, Fe, K, Mg, Na) by ICP‑OES
- Identity check by FTIR (informative)
- Precision and dispute resolution: Precision statements follow ISO 4259; precision data mainly adopted from ISO 22241-2 and summarized in Annex K.
Applications and who uses it
ISO 18611-2 is used by:
- AUS 40 producers and distributors for quality control and certification
- SCR system and catalyst manufacturers to ensure compatibility and reliable converter operation
- Marine engine builders and OEMs to validate fuel‑system inputs and emission control performance
- Ship operators, fleet managers and port laboratories for incoming inspection, acceptance testing and dispute resolution
- Analytical laboratories performing compliance testing using standardized methods (ICP‑OES, FTIR, photometry, combustion analysers).
Related standards
This standard ensures consistent, traceable laboratory methods for AUS 40 quality control, supporting reliable SCR NOx reduction performance and regulatory compliance in maritime emissions control.