Most shipping lines require that shipper-owned containers are in seaworthy condition to be loaded onboard their vessels. 

The container seaworthy certification process involves a thorough inspection of the container, checking for any damages, corrosion, defects in the flooring, loose fittings, and any other potential hazards. The surveyor will also ensure that the containers are structurally sound and meet the requirements to be loaded onboard ocean vessels

When a container is deemed seaworthy, it means that it meets all the safety requirements and standards necessary for marine transport and a certificate is issued that validates the usage of the container for one year.

Containers that are not certified as seaworthy are not allowed on board ships, as they pose a significant risk to both the cargo and the vessel.