Ok, good the THC is off, one less thing.
Pilot arc is still HF but the arc is inside the torch and not from torch to metal. It won't be the issue though i think as all it might do is cause PC or motion problems and you don't have that it seems.
From the ESAB site...
Double Arc
A double arc is a condition which allows the nozzle to stay in the plasma circuit. As described, the nozzle should only be in the circuit during the pilot arc phase. If left in the circuit, the nozzle will carry cutting amperage which will destroy it.
Double arcing is caused by:
Standing pierce. The torch has to be positioned close enough to the work-piece to allow the pilot arc to contact the plate, so the main arc can transfer. Pierce spatter is ejected at a shallow angle during the initial pierce. As the arc penetrates the material the spatter becomes more vertical. This debris may connect the plate and nozzle, keeping the nozzle in the circuit even when the relay opens to remove it. This scenario may damage the front end of the torch.
Torch in contact with the plate. Cutting thin material. All automatic torch positioning systems utilize some initial height sensing method to position the torch above the plate. One method is the touch and retract method. The torch travels until it makes contact with the plate and retracts to the initial start height utilizing a timer or encoder. If the touch is not sensed properly, the torch may still be in contact with the material due to springing up or material warping. The nozzle will remain in the plasma circuit carrying cutting amperage, damaging it.
Pilot arc malfunction. This can occur if the pilot arc relay circuit fails to remove the nozzle. This can happen either with a shorted relay or resistor. Again the nozzle is left to carry more current than intended, damaging it.
Preventing the Double Arc
Double arcing usually occurs during the piercing sequence.
Some techniques which can help avoid double arcing are:
Creep move. The cutting machine is programmed at a reduced speed to begin machine movement on arc transfer. This speed is usually 5 to 10% of normal cutting speed and is for a given time period. Pierce spatter is being ejected away from the nozzle during this time. This reduces double arcing possibility.
Torch rising during standing pierce. On arc transfer the torch begins to pull away from the work- piece. This allows the pierce spatter to clear the nozzle. This retraction continues for a timed period, and then lowers to correct cutting height after the machine is moving at cutting speed.
Higher than normal initial height pierce (standing pierce). This allows the pierce spatter to miss the nozzle reducing the chances for a double arc. This method of prevention is the least effective.
So....
if you manually trigger an arc in free air, you should only see a low power pilot arc, not the full cutting arc, does your unit have current display? As there is no metal to complete the circuit, the unit should not switch to full power arc, just the pilot, if not then maybe a dodgy pilot arc relay etc. You probably won't see this when manually cutting.
I would definitely not exceed the rated power for a nozzle/electrode, in fact my 45A unit cuts best at 43A, go figure