Thanks for your service to our country. As you are wanting to persue piping I would recommend going with the 1104 standard instead of D1.1 THe CWI program test your broad knowledge of welding and the welding process, the ability to accept and reject welds based on a code, and you knowldedge of a specific code. These are the 3 parts of the test. As you have experience and the self dicipline, buying the books and codes and doing a self study process will put you a leg up on any seminar you attend.
With your ability and card to get on bases, your skills as an inspector will be in demand by contractors who do piping and tank work on bases. Shaw,Weston Solutions and Cape do a lot of work on bases and your ability wo get on bases and how to get contractors on base will be a great asset. You have a great career ahead of you. Concentrate on the test and start talking to some of the contractors working around the base. While the fuels guys are not in your circle, hang around the POL area and find out who is working on the fuels equipment. Most bases have a civillian who is in charge of the POL. If they have work going on, offer a site supervisor a ride on your plane and it will suprise you what these guys will turn you on to.
Good luck and welcome to the forum