Polyethylene pressure pipes are black for a reason: well-dispersed carbon black is the most effective UV protection for polyolefins.
Carbon black content
Pipe standards typically require a carbon black content of about 2 to 2.5 percent in the finished pipe. The masterbatch dosage follows from its carbon black content: a 40 percent batch needs about 5 to 6 percent dosage to reach 2 to 2.5 percent in the pipe. Always follow the standard that applies to your pipe.
Dispersion matters as much as content
Agglomerates of carbon black are weak points that can start cracks under pressure. Standards rate dispersion by microscopy, and fine, well-dispersed carbon black in a compatible carrier gives the best results.
Other checks
- Moisture: keep low to avoid voids
- Carrier: match the melt flow of the pipe resin so the batch mixes fully
- Oxidation induction time: carbon black batches should not reduce the pipe's thermal stability
