The four main different PVC pipe categories

About PVC-HI

PVC-HI stands for High Impact PVC. The PVC-HI grade is obtained by adding an impact modifier to PVC-U that increases the resistance of the pipes to external blows.

The minimum requirements for a PVC-HI grade is precisely defined in section 5 of the international standard ISO 6993-1 “Buried, high-impact poly(vinyl chloride) (PVC-HI) piping systems for the supply of gaseous fuels — Part 1: Pipes for a maximum operating pressure of 1 bar (100 kPa)”:

• Composition: PVC-HI shall be one of the following compositions:
  1. a mixture based on PVC
  2. a blend based on PVC
  3. a copolymer based on PVC
  4. a combination of these types
  The proportion of the impact modifier in the composition shall be at least 7 % w
• Long term strength: The MRS value of PVC-HI shall be at least 18 MPa. Conformity to this requirement shall be proven using a long-term evaluation in accordance with ISO 9080. Testing shall be carried out at 20 °C, 40 °C and 60 °C, for periods up to 9 000 h. At 60 °C no knee shall occur before 5,000 h
• Vicat softening temperature: The Vicat softening temperature of PVC-HI shall be at least 76 °C
• K-value: The PVC-U used to make PVC-HI shall be at least 65
• Impact resistance after UV weathering: UV weathered pipe specimen of PVC-HI should not break when a striker of a defined mass is launched from a defined height
• Resistance to gas constituents: no crazes of a depth greater than 30 µm should be observed in pipe specimen of PVC-HI exposed to tetrahydrothiophene and n-hexadecane