PVC Pressure Pipe Surge Rating

[jimtheprez]

PVC pressure pipe has some benefits relative to positive hydraulic transient pressure waves due primarily to the slower wave speed. However, I don't see much (any) documentation relative to PVC pipe performance or ratings under negative pressure. Does anyone have information whether the pipe has a rating or warning relative to vacuum situations? I have a situation where a transient wave will have a negative value under certain conditions and intuitively I wonder if PVC has a weakness in this regard. I would at least like to see some test reports, manufacturers literature, or professional experience on the topic before I move ahead with my design.

 

[stanier]

Buckling is a torrid thing and doesnt always follow the laws of physics.

Timoshenko's formula is applicable for above ground pipe where the soil does not provide any support.

The problem with PVC is that it can become oval rather easily on a construction site. ie sun on the top of the pipe and shade on the bottom. An oval pipe has less capacity to withstand buckling.

You local flexible pipe standard should contain the necessary design criteria. In Australia we use AS 2566.1. You can always purchase this standard as it cover s the topic.

Other texts include
Buried Pipelines by Moser
Structural Mechanics of Buried Pipelines by Watkins
Plastic Pipes for Water Supply and Sewage Disposal by Lars-Eric Janson

Remember that the response criteria to load in thermoplastics is strain rate dependent. Thus an instantaneous load such as in surge will effect an instantaneous value of modulus and this is what should be used to determine the wave speed. But the properties of the PVC to handle the negative pressure wave will also be at a higher instantaneous value.

Research by Molin and Janson in Europe should be sought for a greater understanding.

Sooner or later the advocates of ductile iron will bombard you with negatives about PVC. Read what they have to say with regard from where they are coming from and get a balanced view.