Check out the non-mandatory appendix in B31.1 which discusses and recomends a hanger maintenance program.... I had an owner griping to me about his pipe supports when I asked him if he ever walked them down the response was no.... so I asked him how he could expect them to be okay after cycling, and dynamic loading, time and time again... like driving your car, never changing the oil and getting mad when the engine bites the bullet.... just ignorant!