Where containers fabricated to earlier editions of regulations are to be used, they shall be __________ if they have been properly maintained and requalified.

When containers that were fabricated according to earlier regulations are still in use, it is important to ensure they meet current safety standards despite their age. If these containers have been properly maintained and requalified, they demonstrate that they can still operate safely and effectively. Therefore, it is permissible to continue using them as long as they have undergone the necessary maintenance and requalification processes.

This approach emphasizes the importance of regular inspection and maintenance in the industry. Maintaining compliance with safety regulations allows for the continued use of older containers without compromising safety. The other options suggest actions—like discarding, upgrading, or replacing— that would unnecessarily remove usable equipment from service, which could lead to increased costs and waste when a properly maintained container is still fit for use. The focus on permitting their continued use acknowledges the value of existing resources while ensuring they meet safety requirements.