Googling "piping design courses" turned up several examples. In addition to colleges and universities, you might also look for vocational-technical institutes, or learn on the job with a piping installer.
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I have a series of elementary video based trainings that I basically did as a part of mentoring process to young pipers. Let me know if you are interested and I can send them to you. It includes a cursory introduction complete plant design from FEED to Isometrics. However, it depends on what depth you want to go for a particular training. These days you can get courses from basic to advance in most parts of the world, but they could be expensive (in terms of time and money). Also if you are looking to just advance your knowledge about this field, and satiate curiosity, I would recommend doing some research on the web before really taking any course. Course such as piping design is useless, unless you practically apply what your learned, in the field, and most of the stuff you learn by doing.