I installed copper pipe to replace galvenized pipe that had breakdown and leaks. A hot water heater was intsalled without a dielectric union. I went to my local plumbing place and asked for dielectric unions for my pipe. I was given dielectric nipples instead. Are they the same? Or should I have installed the unions instead of nipples. The gentleman I spoke to stated that they are interchangeable and that the nipple is easier to install. I agree with the ease of installation, but wonder if I am still endangering my galvenized pipe by using nipples instead of unions. Any input would be appreciated.