This document summarizes a presentation on the failure of flexible PVC hose in underground applications. The hose combines rigid and flexible PVC, but failures were found to occur after 1-2 years of use in swimming pools. Microscope analysis found cracks propagating along voids in the flexible PVC, and fracture surface analysis showed stress cracking of the rigid PVC strands due to migration of the plasticizer DOP from the flexible to the rigid component. The conclusions were that use of a non-migrating plasticizer in the flexible PVC could prevent this failure mechanism, and standards should require non-migrating plasticizers to improve durability of these hoses.
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Flexible pvc hose for underground applications
1. Failure of Flexible PVC Hose in
Underground Applications
Presented at âPlastics in Underground Pipes 2011â
Houston, TX / November 1 & 2, 2011
Duane Priddy, Ph.D.
President/Plastic Failure Labs
Plastics in Underground Pipes â Houston DP 11/1/11
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2. Benefits of PVC Hose
âą 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
Plastics in Underground Pipes â Houston DP 11/1/11
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3. Manufacturing Process
âą 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.
Plastics in Underground Pipes â Houston DP 11/1/11
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9. Views of Fracture Surface
Plastics in Underground Pipes â Houston DP 11/1/11
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10. SEM Analysis of Fracture Surface
Plastics in Underground Pipes â Houston DP 11/1/11
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11. SEM of Fracture Surface
Plastics in Underground Pipes â Houston DP 11/1/11
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12. SEM Analysis of Fracture Surface
Plastics in Underground Pipes â Houston DP 11/1/11
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13. FTIR Spectra of Flexible & Rigid Components in Failed Samples
Flexible
DOP plasticizer
Rigid
Plastics in Underground Pipes â Houston DP 11/1/11
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14. Conclusions
âą Some pipe samples contain voids in the
fracture surface and fracture propagation
follows the voids = manufacturing defect
âą Most fractures show evidence of ESC failure of
the rigid strands
âą 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.
Plastics in Underground Pipes â Houston DP 11/1/11
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15. Concluding Remarks
âą Flex hose manufactures should use only flexible PVC
made using non-migrating plasticizer.
âą IAPMO needs to include a requirement in the PVC
flex hose standard requiring only the use of nonmigrating plasticizers.
Plastics in Underground Pipes â Houston DP 11/1/11
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16. Possible Technical Solutions
âą Use a rigid plastic component that is
compatible with flexible PVC; e.g., PP
âą Place a barrier layer between the rigid and
flexible components to stop the DOP
migration
âą Develop a low cost non-migrating plasticizer
Plastics in Underground Pipes â Houston DP 11/1/11
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