IF the OP is pumping seawater to some terrestrial installation, like a salt concentration pond, or a desalinator, and the CPVC is protected from sunlight, and collateral damage from pipe fracture is limited to some incidental leakage that does no serious harm, then I'm okay with using it.
IF the OP is pumping seawater within a boat, then I have a problem with using CPVC.
First, the seawater sucked into a boat is not necessarily nice clean salt water; it includes whatever has been dumped into the water in which the boat finds itself. The boat crew has no control over the composition.
Second, seawater is typically used within a boat to cool the engines. It typically takes a lot of seawater to do that, and the systems within the engine room are normally unattended, so a breach of the seawater piping can quickly flood the engine room, which often enough causes loss of the entire boat. That is a serious risk of considerable collateral damage, which does not balance well against a small savings achieved by not using serious marine grade material.
The OP has not come back to clarify the application, so an unconditional blessing of CPVC for 'seawater service', without further elaboration of the service's exact nature would be irresponsible.
Mike Halloran
Pembroke Pines, FL, USA