The NOx Technical Code (the "Technical Code on Control of Emission of Nitrogen Oxides from Marine Diesel Engines", adopted by IMO Resolution MEPC) is a mandatory annex instrument under MARPOL Annex VI (Regulation 13). Its purposes:

• To prescribe the procedures for the certification (survey and testing) of marine diesel engines to verify they meet the applicable NOx emission limits (the Tier).
• To define the requirements for the engine's NOx Technical File, the EIAPP certificate, the procedures for the measurement and verification (including the engine test), and the record/execution of emissions.
• To provide a standardised, internationally agreed way of measuring NOx emission, so that flags/ROs/port States can consistently verify compliance, and to ensure that engines fitted with emission control devices (e.g. SCR) are effective.
• To provide the sampling methodology, the engine test cycle and the requirements for verifying compliance at survey.

Applicability: The Code applies to marine diesel engines above 130 kW (i.e. essentially all main and auxiliary engines, and any additional/purpose engines) installed on ships subject to MARPOL Annex VI - those installed on ships keel-laid after 1 January 2000 (Tier I), 2011 (Tier II), and the NECA (Tier III) for the respective dates - and to engines whose propulsion/auxiliary drive output is in the covered range. Certain engines are exempt/derated (e.g. some emergency engines, engines on ships with no certification by the flag? but generally covered; small engines below 130 kW are excluded). The Certification requires a survey by the flag/RO of the engine (a pre-certification by the manufacturer and the "site survey"/EIAPP) and the issue of the EIAPP, with the NOx Technical File carried on the ship.

• Pre-certification: the engine (or class/type) is tested by/for the manufacturer on the test bed, using the specified test cycle, to measure the NOx emission value (g/kWh) and establish the components/settings.
• Onboard survey/certification: the engine is surveyed at installation; the surveyor verifies engine particulars, the components/settings, and issues an Engine International Air Pollution Prevention Certificate (EIAPP certificate) accompanied by the NOx Technical File; the certificate is valid for the life of the engine unless modified and is entered in the IAPP.
• The EIAPP is renewed/endorsed at the ship's surveys and any major modification requires re-certification.
• The NOx Technical Code gives the "engine parameters" (adjustment certificate) to be recorded (e.g. injection timing, rail pressure, valve timing, the emission control setting) so any change is detectable.
• The engine must be operated in accordance with the Technical File; ongoing verification is by the surveyor checking the file and the parameters.

(Refer to the detailed answer for 694a8e... .) Purpose: The NOx Technical File documents the technical information and the settings which ensure the engine meets its NOx limit, enabling verification. Importance: It is the primary record carried on board that proves (with the EIAPP) the engine's compliance, allows the flag/RO/port State to verify the engine has not been modified outside the certified parameters, supports planned maintenance and any adjustment, and is essential for the IAPP survey and port State control - without it the vessel is non-compliant and may be detained/fined.