Galvanized steel pipes are used as far as possible in underground laying projects, and the anticorrosion process can be omitted. When the inner wall of steel pipe is coated with camphor oil for anticorrosion, round steel can be welded into a painting operation frame that can hold several steel pipes. Steel pipes are placed on the operating frame in a staggered and inclined way, and the pipes are connected in series with transparent plastic hoses. The top layer of the nozzle is filled with plumbum preparatium paint, which is naturally discharged from the bottom layer of the nozzle, and then the inner wall of the pipe can be painted.

Sc is welded steel pipe. These two kinds of steel pipes are somewhat different. The former needs to bend the steel strip before welding, and the latter can be directly welded on the basis of welding steel pipes. The welding methods of the former generally include arc welded pipe, furnace welded pipe and so on. And the latter welding methods are only cold-coated pipe and hot-coated pipe.

For the welding of large-diameter seamless pipes and parts, the coated covered electrode and welding wire can be dried, kept warm and stored in a heat preservation barrel. When the temperature of welded parts in the pipeline is lower than 0℃, all steel parts and welds must be preheated to 15℃ or higher within the initial welding range of100 mm. The method of using scaffolding to ensure preheating, gas welding to ensure ignition and local heating.