We do not know what you mean by "PFD", please do not use abbreviations. But the answer would be when the instructions for the "PFD" say it needs to be replaced.
discard because they are unusable
Every time the PFD is worn
When selecting a PFD, the most important consideration should be size.
A Personal Flotation Device (PFD) should be discarded if it shows signs of significant wear, such as tears, holes, or damage to the buckles and straps. Additionally, if it has lost buoyancy or its inner foam has deteriorated, it is no longer effective and should be replaced. Regular inspections are important to ensure the PFD remains in good condition for safety. Always follow the manufacturer's guidelines for lifespan and maintenance.
Every time the PFD is worn
When selecting a PFD, the most important consideration should be size.
Every time the PFD is worn
Every time the PFD is worn
Every time the PFD is worn
Every time the PFD is worn
Securely fasten your PFD, and wait for help.