Check valves in vertical lines are only permitted if the flow is upward.
Check the latest edition (e.g., or newer). Always use the current revision for new projects. norsok l002 pdf
Unlike the ASME B31.3 code, which provides broad rules for process piping, NORSOK L-002 serves as a specific, supplementary standard that prioritizes safety, operability, and maintainability in harsh offshore and onshore environments. It is widely regarded as one of the most stringent standards for piping layout globally. Check valves in vertical lines are only permitted