Hello Odie, I would guess your client has concerns about having tungsten contamination of the weld metal. Even though you have been welding pipe forever and obviously having very good success doing it a particular way, your client in this case, has a preference to have it done using the hi-freq. method. With a hi-freq. start there is no possibility of any sort of tungsten contamination of the weld metal. Argueably you could still possibly end up with a really minimal amount of contamination by striking the tungsten off of the end of the rod when you make the type of start that you are used to.
A hi-frequency start allows the arc to be started without ever touching the tungsten to the workpiece or the rod and thus avoids any possiblity of tungsten contamination of the work piece, unless you accidentally strike it with the rod or accidentally touch the tungsten to the work. There is a possibility that starting the arc by touching the filler rod between the tungsten and the work can still burn off a small bit of the tungsten and introduce this into the weld metal. This might be the concern that your particular client has with this arc starting method. Just a few thoughts to consider. Regards, aevald