ClassNK grants Approval in Principle (AiP) for methane oxidation catalyst system to Mitsubishi Heavy Industries Marine Machinery & Equipment and Mitsubishi Shipbuilding

22 April 2026 – ClassNK has issued an Approval in Principle (AiP) for methane oxidation catalyst system* to Mitsubishi Heavy Industries Marine Machinery & Equipment Co., Ltd. and Mitsubishi Shipbuilding Co., Ltd. The certification demonstrates its feasibility from regulatory and safety perspectives.

As efforts toward decarbonization accelerate, the development of alternative fuel vessels is progressing. In the operation of LNG-fueled engines, however, methane slip—unburned methane released into the atmosphere—remains a challenge. Methane has a particularly high global warming potential among greenhouse gases, and therefore, catalyst systems capable of reducing methane slip through oxidation have attracted increasing attention. This system was installed as a demonstration unit on the LNG bunkering vessel KEYS Azalea, constructed by Mitsubishi Shipbuilding Co., Ltd., and has been undergoing demonstration testing.

ClassNK reviewed the design concept of the system based on chapter 21 of part D of its “Rules and Guidance for the Survey and Construction of Steel Ships”. Upon confirming compliance with the prescribed requirements, ClassNK issued an AiP. This AiP demonstrates that the design is feasible for the intended application and contributes to the prevention of regulatory rework in subsequent stages as well as the reduction of the time required for classification approval.

ClassNK will continually strive to contribute to advanced decarbonization initiatives through safety assessments and more.

＊The device is designed to reduce methane slip by placing a methane oxidation catalyst in the exhaust of an LNG-fueled engine or generator that contains unburned methane and oxidizing the methane over the catalyst

Methane oxidation catalyst system (courtesy: Mitsubishi Heavy Industries Marine Machinery & Equipment)

Approval in Principle (AiP):
At the initial stage of designing or before the specific target ship to be implemented is decided, the design is examined based on the existing regulations such as international conventions and ship classification rules, and an Approval in Principle (AiP) is issued as proof of conformity with requirements. For more information, visit our website.