The welding and working principle of the core component plate bundle of FUNKE box type semi detachable welded plate heat exchanger (Flex FPF) is the same as that of box type detachable welded plate heat exchanger, but the difference is that the box shell of this type of plate heat exchanger is not completely detachable. The design of this structure improves the design pressure and design temperature of the product. The design pressure can reach 40bar, and the design temperature can reach - 40 ℃~600 ℃ FUNKE Flex FPF has been successfully used in the application of power plant steam condenser and flue gas waste heat recovery.