What is the reason for the leakage of the full clamp joint of the pneumatic valve gas pipeline?

The pneumatic valve and gas pipeline of the unit device are both connected by a ferrule connector. After installing it, it is pressed, and 95% are leaking and depressed. The pipe is made of 8 mm stainless steel pipe (unpolished). Is it necessary to use bare tubes for clamping joints? Now that the instrument air pipeline has been built, is there any good way to completely replace the stainless steel polished pipe and rework it? I tried wrapping raw tape, which can be sealed, but it seems that there is no such method, and I am afraid that the tape will be blown into the pipeline to block the pressure reducing valve, and that will be over. What should I do? Sad! In addition, the process interfaces of the transmitter are all tapered threads, and the original belt is wound during installation. The leader said that it is not recommended to wrap the raw material belt, and the taper thread can be directly sealed, and the raw material belt is easy to age and leak. After the knot, it was pressed with raw tape, gas leaked, or Rosemount's transmitter. Damn taper thread seal is pure nonsense, and the machining accuracy is really not that good. By the way, the thread is absolutely tightened, but it won't seal. How is your equipment?