I agree to greybird as u see there are various other pumping solutions ( Diaphragam pumps specially designed ) which may solve your purpose if flow rate requirements are so high .
Tickle , I feel there are cold pipe applications in Marine paints category , specific details I will sent you soon , any way its always advisable to have coat of material which may form a protective chemical layer or coat the pipe before submerging it .
D.K.Shukla