English: A polyethylene gas main being laid in a trench under Chesterton Road, Cambridge. The bright yellow polyethylene (PE) pipes have been used to replace older ductile iron pipes since the 1970s. Once complete, the pipeline will operate at a pressure of 75 millibar since it is directly supplying domestic premises. However, the pipes can be run at up to 10 bar. Gas main pipes in the UK are generally 250mm in diameter. The smaller diameter pipe branching off the main pipe is for domestic supply.