piping material for seawater service

[baherfm]

What are the restrictions on using plastic pipes (pvc or PE) for seawater underground pipes instead of using carbon steel internally painted and externally insulated in addition to cathodic protection???

 

[LittleInch]

Pressure and temperature are more limited in PE / PVC than steel - max is about 16 bar, max temp 50 deg c (lower pressure) for PE. C steel can corrode very quickly (several mm/year) in the presence of warm aerated sea water and internal "painting" is probably not good enough for a long life. CP works well on external coatings, but doesn't work internally or not that I've ever heard... when you say insualted do you mean coated or insulated - there is a big difference.

Gve us a bit more of your intended use (flow rate, size, pressure, depth etc) and you may get more info

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way