It might make it a little more safe, but it won't increase the pressure rating. Pressure ratings are a result of standards, testing, and the work of professional engineers.
Plus you still have the fittings at the end of the pipe that are rated at the same pressure of the pipe that they are for, and finding a way reinforce the fittings is more trouble than it is worth. Just upgrade the size of the piping or upgrade materials.
It depends on how you do it, but most double walling is mostly cosmetic. It may provide some impact protection, but like I said above unless you go to a lot of trouble, the fittings on the ends are still vulnerable.