Which of the following is NOT a type of flexible pipe?

Flexible pipes are characterized by their ability to bend and conform to changes in the environment without breaking or suffering significant damage. PVC, or polyvinyl chloride, is a type of rigid plastic and does not possess the flexibility characteristic of the other options listed. While PVC can be used in various applications and is popular in water distribution, it typically requires fittings and joints to accommodate changes in direction, making it less flexible than true flexible pipe materials.

Ductile materials, steel structures designed with flexibility in mind, and thermoset plastics can all exhibit significant bendability, allowing them to absorb movement and pressure changes without compromising their structural integrity. Thus, PVC stands out as the option that does not fit within the category of flexible pipe types.