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        # UPVC Pipe Extrusion: Achieving IS 4985 Indian Standard Compliance

        

**Topic:** Explainer

        

Extruding rigid pipes conforming to potable water standard **IS 4985** requires careful control of resin K-value and filler loading. Using high-purity resins, lubricants, and impact modifiers like [NBT CPE 135A](/products/additives/cpe) ensures pipes pass falling weight impact and hydrostatic tests.

        
        
        
        
        
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          ## Frequently Asked Questions

          
### Why do UPVC pipes fail the falling weight impact test?

Failure is almost always caused by: (1) Over-filling with calcium carbonate (above 10 phr), which creates stress concentration sites; (2) Incomplete fusion (gelation) due to low processing temperatures; or (3) Using coarse, uncoated filler that does not disperse.

### What K-value is best for UPVC pressure pipes?

PVC suspension resin with a K-value of 65 to 67 is specified. It provides the optimal molecular weight to meet the 45 MPa tensile strength requirement while remaining processable on twin-screw extruders.

### Is lead stabilizer permitted in potable water pipes in India?

India is phasing out lead stabilizers in potable water pipes due to lead leaching concerns. The industry is transitioning to Ca-Zn stabilizers, which are fully non-toxic and compliant.

### What is the maximum light transmission for UPVC pipes?

To prevent algae growth inside the pipe, the light transmission must be strictly ≤0.2% when tested per IS 4985 opacity guidelines. This requires adding adequate TiO2 and carbon black colorants.

        
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By NBT Technical Desk · Updated 2026-07-04

        

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