flexible pvc hose for underground applications

Failure of Flexible PVC Hose in Underground Applications

Duane Priddy, Ph.D.

President/Plastic Failure Labs

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Presented at “Plastics in Underground Pipes 2011” Houston, TX / November 1 & 2, 2011

Benefits of PVC Hose

• Semi-flexible PVC hose combines the attributes of rigid PVC (high modulus) with flexible PVC (high flexibility) to yield a product that has the benefits of PVC pipe (easy to install using standard glued PVC fittings) yet it is semi-flexible allowing it to be installed with flexing around underground obstructions

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Manufacturing Process

• The hose is manufactured using a co-extrusion process where the rigid PVC formulation is extruded into a strand along side of the flexible PVC formulation which is extruded into a narrow sheet. As the strand and the sheet co-extrude from the die, they are wound around a mandrel to form the hose. The rigid PVC strand ends up embedded in the wall of the hose as a helical coil.

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Example Failures: Swimming Pools

These failure occurred after 1 – 2 years of service

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Exterior Cracking is Most Common but also may Occur on Either the Interior Wall

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Microscope Views of Cracks

Close-up view of failed region in outside hose wall

View of fractures surface shows repeating diagonal void pattern in flexible PVC portion

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Fracture surface analysis

Closer view of the voids

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Views of Fracture Surface

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SEM Analysis of Fracture Surface

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SEM of Fracture Surface

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SEM Analysis of Fracture Surface

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FTIR Spectra of Flexible & Rigid Components in Failed Samples

Flexible

Rigid

DOP plasticizer

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Conclusions

• Some pipe samples contain voids in the fracture surface and fracture propagation follows the voids = manufacturing defect

• Most fractures show evidence of ESC failure of the rigid strands

• Flex hoses that use flexible PVC containing a migrating plasticizer are inherently defective because the plasticizer migrates into the rigid PVC strands causing them to stress-crack.

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Concluding Remarks

• Flex hose manufactures should use only flexible PVC made using non-migrating plasticizer.

• IAPMO needs to include a requirement in the PVC flex hose standard requiring only the use of non-migrating plasticizers.

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Possible Technical Solutions

• Use a rigid plastic component that is compatible with flexible PVC; e.g., PP

• Place a barrier layer between the rigid and flexible components to stop the DOP migration

• Develop a low cost non-migrating plasticizer

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