The essential differences
| Characteristic | AUS32 | AUS40 |
|---|---|---|
| Nominal urea content by mass | 32.5% | 40% |
| Product standard | ISO 22241 | ISO 18611 |
| Selection rule | Use the concentration and quality specification approved by the engine/SCR manufacturer. | |
Why concentration matters
A dosing system is configured for a particular reagent specification. Changing concentration changes the urea delivered for a given quantity of solution and may affect dosing, emissions performance and equipment operation. Do not assume that the controller automatically compensates.
Not every marine SCR installation is the same
Vessel size or type alone does not establish which reagent is permitted. Check the engine/SCR manual and approved technical documentation. If a system specifies AUS40, do not replace it with AUS32 or dilute the product without explicit OEM approval.
Before purchasing
Send the supplier the required product concentration and standard. Verify the batch CoA and keep the receiving tank and transfer equipment free from contamination. See the product-document checklist.
References
Common questions
What is the difference between AUS32 and AUS40?
Concentration and standard. AUS32 is 32.5% urea by mass to ISO 22241; AUS40 is 40% urea by mass to ISO 18611. AUS32 is the automotive reagent sold as AdBlue; AUS40 is the marine reagent. Use whichever your engine or SCR manufacturer specifies.
Can I use AUS32 instead of AUS40?
Not without explicit OEM approval. A dosing system is configured for a particular reagent specification, and changing concentration changes the urea delivered per litre of solution. Do not assume the controller compensates automatically.
Can I dilute AUS40 to make AUS32?
No. Diluting a certified product destroys its conformity and its documentation, introduces contamination risk, and produces a fluid nobody has tested. If the vessel needs AUS32, buy AUS32.
Does vessel type tell me which reagent I need?
No, and this is a common and expensive assumption. The reagent is set by the engine and SCR approval for that specific installation, not by whether the ship is a bulker, tanker or container vessel. Check the manual.
Why is marine urea more concentrated than automotive?
The marine standard specifies a 40% solution. That carries more urea per litre than a 32.5% solution, which matters where onboard tank capacity is a design constraint. The practical point for a buyer is simply to match the specification the installation was approved against.