What are the standard requirements for polyurethane directly buried finished insulation pipes? Firstly, the insulation layer thickness of the polyurethane directly buried finished insulation pipe should ensure that the outer protective pipe can be used normally within the temperature range of -50 ℃ to+50 ℃. Both ends of the steel pipe should be left with an exposed non insulated area of 150mm to 250mm for welding. Secondly, before and after foaming the polyurethane directly buried finished insulation pipe, the increase rate of the outer diameter of the same section at any position of the o