Why do firefighters use plastic-coated steel pipes inside and outside

in 2010, china promulgated gb/t5135.20-2010 automatic sprinkler fire protection system, among which part 20 coated steel pipes stipulates that the fire sprinkler fire protection system should use internal and external plastic coated steel pipes as materials.

so what is the difference between the inner and outer plastic-coated steel pipes and ordinary galvanized pipes?

anti-water supply plastic-coated steel pipes use steel pipes as the base pipe, use plastic powder (such as epoxy resin) as the coating material, coat a layer of plastic on the inside and outside, and coat a layer of plastic on the outside and other anti-corrosion materials layers of steel pipes. the surface is smooth, reduces fluid resistance, reduces flow resistance, increases flow, and does not scale, and is not easy to breed microorganisms. it solves the corrosion and scaling problems of ordinary fire water supply steel pipes buried in the ground and water delivery, without the appearance of blocking pipes and sprinkler heads, and improves the service life of fire water supply pipelines. the service life is theoretically up to 50 years, and now it has been used for more than 10 times so far, and it is safe and outstanding. the use together reduces maintenance costs and saves the cost of replacing pipes. for the coating material of the spray fire pipe, we all chose epoxy resin, the first is because the flame retardancy of epoxy resin is better than other materials; the second is because the adhesion of epoxy resin is better than other coating materials it is much more reliable and stable, so in the event of a serious fire, we can feel the stability and cost-effective advantages of epoxy resin through relevant tests at this point.