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.

1. Failure of Flexible PVC Hose in
Underground Applications
Presented at “Plastics in Underground Pipes 2011”
Houston, TX / November 1 & 2, 2011
Duane Priddy, Ph.D.
President/Plastic Failure Labs
Plastics in Underground Pipes – Houston DP 11/1/11
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2. 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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3. 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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4. Plastics in Underground Pipes – Houston DP 11/1/11
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5. Example Failures: Swimming Pools
These failure occurred after 1 – 2
years of service
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6. Exterior Cracking is Most Common but also may
Occur on Either the Interior Wall
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7. 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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8. Fracture surface analysis
Closer view of the voids
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9. Views of Fracture Surface
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10. SEM Analysis of Fracture Surface
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11. SEM of Fracture Surface
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12. SEM Analysis of Fracture Surface
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13. FTIR Spectra of Flexible & Rigid Components in Failed Samples
Flexible
DOP plasticizer
Rigid
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14. 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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15. 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 nonmigrating plasticizers.
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16. 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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