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Wave speed for a pipe with a flexible internal liner system

Hi

I'm looking for any guidance / experience in calculating wavespeed and considering transient performance in a section of asbestos cement pipe pipe which will be re-lined using a flexible liner system. The liner product is semi-structural and inserted in a folded form and then inflated, and is made up of various plastic/fabric layers. There will be some small annulus remaining between the liner and host pipe (i.e. not a close-fit liner system) which will not be grouted but is expected to fill with water over time. 

The system will be subject to some transient behaviour, the most significant likely to be occasional low/vacuum pressures if the upstream pump stops suddenly/loses power. In normal operation the pump starting and stopping will be at a controlled rate which will minimize transients. 

For positive transient pressures, is it reasonable to assume the pressure will be transferred to the host pipe and result in a similar (much higher) wavespeed to the host pipe? at least as a worst case (i.e. resulting in the highest wave speed)

For negative transient pressures, the above approach would seem to remain valid (at least as a worst case) providing pressure remains above the full-vacuum / vapour pressure and the internal water column does not collapse. At full vacuum / vapour pressure however, the liner pipe might collapse/deform, which is unlikely to damage it, but this might also cause (or require) the water in the annulus to vaporize. Is it possible in this case the section of pipe may behave more like some kind of pressure vessel and have a significant damping effect on the transient? As a worst case would this result in wavespeed of the host pipe remaining applicable/valid? or is this just too unpredictable / un-knowable for meaningful analysis?

Any thoughts / experience welcome

Below are a couple previous posts I found on similar questions, although these were just dealing with wavespeed for composite pipes with a PE liner, which is full structural liner pipe and would be able to resist collapsing

thanks,

Jack

communities.bentley.com/.../26659.aspx

https://communities.bentley.com/products/hydraulics___hydrology/f/haestad-hydraulics-and-hydrology-forum/54711/hammer-wave-speed-calculator/184877#184877

Parents
  • Jack,

    It may be difficult to determine exactly how this pipe would behave during a transient simulation. It may be best to approach this as a calibration exercise: try using high frequency data loggers to measure the actual wave speed in a few samplings of this type of pipe and make sure your model wave speed matches reasonably close. The deformation and partial-elasticity of a pipe would mainly impact the wave speed for significant lengths.

    As for the potential to collapse, we may need to hear from other community members who might have experience with this type of situation. There may also be journal or research papers on the topic.


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.

Reply
  • Jack,

    It may be difficult to determine exactly how this pipe would behave during a transient simulation. It may be best to approach this as a calibration exercise: try using high frequency data loggers to measure the actual wave speed in a few samplings of this type of pipe and make sure your model wave speed matches reasonably close. The deformation and partial-elasticity of a pipe would mainly impact the wave speed for significant lengths.

    As for the potential to collapse, we may need to hear from other community members who might have experience with this type of situation. There may also be journal or research papers on the topic.


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.

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