Hi Allen
Actually plastic pipe between the pump and CSV should be fine as long as the pump doesn't get hot. A J10S has a max pressure of 76 PSI. So if your pressure switch shuts off the pump at 66 PSI or lower, the 10 PSI differential will push enough through the CSV to keep the pump cool. If your shut off is higher that 66 PSI, the water in the pump may get hot and soften plastic pipe.
Also if you lose prime the pump will get hot. It is better to have a foot valve only and not a check valve on on a jet pump system, to prevent losing prime.
You can also use a Cycle Sensor as a protector to shut the pump down if it loses prime, which it will do long before the pump gets hot.
Changing to a galv nipple will only move the hot water problem to the pump. If the nipple had not melted and started to leak, you would have probably melted the pump instead. Still have to fix the real problem which is working at too high a pressure or losing prime.