The straight sections of plumbing systems are called "pipes" or "tubes". A pipe is typically formed via casting or welding, whereas a tube is made through extrusion. Pipe normally has thicker walls and may be threaded or welded, while tubing is thinner-walled and requires special joining techniques such as brazing, compression fitting, crimping, or for plastics, solvent welding. These joining techniques are discussed in more detail in the piping and plumbing fittings article.
I was disappointed with the pressure of a tub and shower that were plumbed with 1/2 supply lines (2nd floor). Could be low pressure from the street, but I want to replace with 5/8. Plus, I'd like to have 2 back to back showers, one inside and one outside. So, I had intended to bring a 1 supply to both, then branch up to valves and shower head with 5/8. Finally, I thought pressure from the street was typically 55 to 70 psi and I am concerned if pvc can take that.Any thoughts?