flexible pvc hose for underground applications
DESCRIPTION
Root cause of failure of flexible PVC hose used in swimming poolsTRANSCRIPT
Failure of Flexible PVC Hose in Underground Applications
Duane Priddy, Ph.D.
President/Plastic Failure Labs
Plastics in Underground Pipes – Houston DP 11/1/11 1
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
2 Plastics in Underground Pipes – Houston DP 11/1/11
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.
Plastics in Underground Pipes – Houston DP 11/1/11 3
Plastics in Underground Pipes – Houston DP 11/1/11 4
Example Failures: Swimming Pools
These failure occurred after 1 – 2 years of service
Plastics in Underground Pipes – Houston DP 11/1/11 5
Exterior Cracking is Most Common but also may Occur on Either the Interior Wall
Plastics in Underground Pipes – Houston DP 11/1/11 6
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
Plastics in Underground Pipes – Houston DP 11/1/11 7
Fracture surface analysis
Closer view of the voids
Plastics in Underground Pipes – Houston DP 11/1/11 8
Views of Fracture Surface
Plastics in Underground Pipes – Houston DP 11/1/11 9
SEM Analysis of Fracture Surface
Plastics in Underground Pipes – Houston DP 11/1/11 10
SEM of Fracture Surface
Plastics in Underground Pipes – Houston DP 11/1/11 11
SEM Analysis of Fracture Surface
Plastics in Underground Pipes – Houston DP 11/1/11 12
FTIR Spectra of Flexible & Rigid Components in Failed Samples
Flexible
Rigid
DOP plasticizer
Plastics in Underground Pipes – Houston DP 11/1/11 13
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.
Plastics in Underground Pipes – Houston DP 11/1/11 14
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.
Plastics in Underground Pipes – Houston DP 11/1/11 15
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
Plastics in Underground Pipes – Houston DP 11/1/11 16