Which of the following is NOT a requirement for metallic flexible joints used in the pipeline for vibration control?

The option that states a minimum length of 12 inches is not a requirement for metallic flexible joints used in pipelines for vibration control. Instead, the focus for these joints is more fundamentally on their function and capability rather than strict length specifications.

Metallic flexible joints are designed to absorb vibrations and accommodate movement caused by thermal expansion or other stresses. The materials used must ensure durability and functionality, which is why criteria such as being suitable for service at 150 psig or above, having the ability to accommodate thermal expansion, and being made from corrosion-resistant materials are essential. These requirements help ensure that the joints can withstand the operating conditions of medical gas systems without failure or degradation.

Length may be relevant in some contexts to ensure effective vibration control, but it is not universally mandated as a specific requirement like the other options mentioned. This highlights the more critical aspects of flexible joints concerning safety and performance in the field of medical gas systems.