What pipe is especially prone to sliding out of a push on joint?

• A. PVC pipe
• B. Steel pipe
• C. Copper pipe
• D. Plastic Encased Pipeline

Answer: (D)

Push-on joints rely on a tight interference fit between the spigot and bell and on a rubber gasket to seal. A plastic-encased pipeline carries a plastic jacket around the pipe, which can creep or shift and reduce the grip at the joint. That softer, slippery outer layer can allow the spigot to back out under pressure or movement, making sliding out more likely than with uncoated pipe. Other materials with push-on joints don’t have that same encasing effect, so they’re less prone to this particular failure mode. To prevent it, use proper restraints such as thrust blocks or retainer devices at joints exposed to high thrust or movement.