Are there guidelines for converting LNG ships into H2-driven ones? The project in question uses hydrogen as fuel in combination with fuel cells (partly for the hotel load or for smaller vessels even for propulsion).

LNG storage, plumbing, and other systems can’t be directly retrofitted to handle hydrogen. The LNG components and systems will need to be removed and replaced with equipment specifically designed for hydrogen. If the concept is to convert existing equipment or an existing ship, then it’s probably impossible. If it’s to convert an existing LNG design on paper, then it’s probably impractical. Much better to start from the ground up with an H2 design.

From a materials perspective, there would be issues related to both the lower temperature of hydrogen and hydrogen embrittlement.   The temperature of LNG is 113 K, so many materials specified for this temperature will not be suitable for liquid hydrogen’s temperature of 20 K. In addition, liquid hydrogen’s lower temperature will condense air, so insulation systems will need to be significantly different for vessels and piping.

Another consideration is that electrical classification for LNG is different than H2, so would likely require substantial retrofit of instrumentation and controls. LNG equipment also frequently has non-captured vents, which would not be acceptable for hydrogen. Much of the LNG equipment might be located in enclosed areas, in which case the properties of H2 are going to drive design changes. Enclosed areas may also be a hazard for LH2 systems since air may condense on the piping and create a localized oxygen rich environment, especially if poorly ventilated.