Pressurized natural gas (PNG) is a solution for maritime transport of compressed natural gas. Knutsen OAS Shipping has together with EUROPIPE GmbH and Det Norske Veritas developed a new solution for Compressed Natural Gas transport with the proprietary name PNG®.

The Knutsen OAS Shipping approach was to develop a CNG solution that could load and discharge gas onshore and offshore using elements from existing technology already in use within the shipping and the oil/gas industry. To meet this objective, the Knutsen PNG solution has been developed based on an interdisciplinary iteration process to ensure that PNG provides safe, efficient and economical gas transport for value chains earlier considered uneconomic using other gas transportation alternatives.

The idea of being able to transport gas at ambient temperature and high pressure is equally old as the LNG development. The Compressed Natural Gas (CNG) option seemed especially tempting as this would allow for cost-savings in liquefaction, storage and regasification installations. Hence, the cost of land based infrastructure could be significantly reduced and also enable more flexibility in use of the ships as they would not be as dependent on a tailor made infrastructure being in place as is the case for LNG. This can also open up for offshore loading of gas direct from the gas source using established well proven offshore loading principles.

In the startup of the development, this technology encountered challenges due to previous pipeline regulations. However, important technological developments within high strength materials, welding, non-destructive testing and production have taken place during the last decades mainly due to the oil companies requirements to install oil and gas pipelines into deeper water and over longer distances. The development has been accepted and explicit risk acceptance criteria have been implicitly set. The new pipeline standards of today are more or less based on the above technological development improving project economics without jeopardizing safety. One of the most used pipeline standard worldwide is the DNV standard for submarine pipelines. For design against burst, the steel weight of the cargo tanks may be reduced by 50% compared with the pressure vessel code. By defining the correct failure modes for CNG containment system based on submarine pipeline technology with proven track record, CNG can emerge as an economically viable option. This is the basis for the PNG technology.

This new technology opens for new transport alternatives especially suitable for offshore loading for direct transport to the market. Gas is stored on board ships in specially designed cylinders at a pressure of 250 barg. In comparison to LNG maritime transport, the gas treatment is minimal and comparable to treatment required for pipeline transport. The reduction in energy recourses required to compress the gas makes is a more environmental friendly solution than LNG.

The PNG project has been in an active phase of development, both technically and commercially. Technically the Knutsen Technology has in close cooperation with the world’s leading classification society Det Norske Veritas (DnV) and the world leading pipeline manufacturer EUROPIPE GmbH. Analyses show that the PNG solution is competitive for many alternative gas supplies scenarios compared to both pipeline and LNG transportation. A number of companies are working to create solutions for transportation of CNG (Compressed Natural Gas) which is the general industry term of which PNG is one such solution.