You'd be more 'salable' as a 'piping layout designer' or just a 'piping designer', rather than a 'hydro power plant piping layout designer'.
A few bits of information will have to be extracted or deduced from representative old drawings, or from peers in that specialty. E.g. paper mill pipes carrying paper stock need to be ground smooth inside, relatively free of crevices where microbes can hide, and self-draining as much as possible.
Aside from stuff like that, pipes are pipes, and the details of a particular plant will mostly be spelled out in excruciating detail in a thick specification and a set of company standards, which you will end up memorizing, whether you want to or not.
Mike Halloran
Pembroke Pines, FL, USA