The gas pipeline is generally very long, and should be divided into sections and pipelining, that is, according to the construction force, reasonable arrangement, divided construction, pipe trench excavation, immediately install the pipeline, at the same time excavation of the next section of pipe trench. Complete a section, immediately backfill pipe trench, avoid long distance pipe trench long-term exposure caused by the impact of traffic, safety accidents, pipe mouth corrosion, corrosion layer damage, ground water (or rain) into the pipe trench caused by trench wall collapse, trench bottom subsidence, pipe sinking or floating, water in the pipe, pipe wall corrosion and other accidents.
Section construction is to ensure the engineering quality, reduce accidents, to speed up the construction schedule, the effective measures to reduce the project cost, which requires reasonable organization digging, pipe assembly, welding (or twist the mouth), segments, strength test and leak test, purging, steel tube joint anticorrosive mouth, backfill soil, etc., try to shorten the construction period.
Seamless steel pipe transportation and piping should be done as far as possible after the trench is dug. The seamless steel pipe shall be arranged on the other side of the trench pile, and the safe distance between the trench edge and the outer wall of the steel pipe shall not be less than 500mm. It is forbidden to lay pipes on the side of the trench and then dig pipes. The soil, bricks and stones are pressed on the pipes to damage the anticorrosion layer and seamless steel pipe, so that the pipes are loaded with soil. When piping, attention should be paid to the end of the connection. In the street pipe, as far as possible on the side of the pipe, do not affect the traffic, avoid vehicles and other damage to the pipeline, and try to shorten the placement time of the pipeline on the road.
Underground gas pipelines are used with steel pipes. In order to prevent corrosion of steel pipes, epoxy coal asphalt anti-corrosion insulation layer, coal tar enamel coating and petroleum asphalt anti-corrosion insulation layer are commonly used. The anti-corrosion insulation layer is generally prefabricated in a centralized way, and then shipped to the site for installation after passing the inspection. In the process of pipeline transportation, stacking, installation and backfilling, the anti-corrosion insulation layer must be properly protected to extend the service life and safe operation of the gas pipeline.
Transportation and piping
The quality certificate and the appearance quality of the anti-corrosion insulation layer should be checked when the seamless steel pipe is shipped in the prefabrication plant. If necessary, the thickness, adhesion and insulation can be checked before shipment.
1. Coal tar enamel coating coating anticorrosive steel tube coal tar enamel low temperature when easy brittle crack, according to the coal tar touch paint of different models, the provisions of different can carry the lowest environmental temperature. Do not transport or transport when the temperature is expected to be equal to or lower than the minimum ambient temperature for handling. Because the coal tar enamel coating is thick and easy to bruise, a wider nylon belt spreader should be used. When the truck is transported, the seamless steel pipe is placed on the wide wooden bracket whose supporting surface is arc, and the steel wire rope of fastening seamless steel pipe should be padded well. Seamless steel tubes shall not collide with each other during transportation. in railway transportation, all seamless steel pipes shall be carefully mounted on padded brackets or pads, all supporting surfaces and shipping bars shall be well padded, and the joints shall be separated so that they do not collide with each other. Coal tar enamel anticorrosive steel pipe welding, rolling welding is not allowed, requires fixed welding, to protect the coating. Therefore, after the trench is dug, the welding pit will be dug, and the seamless steel pipe will be lifted directly from the car to the trench, so that it is in place. When the seamless steel pipe is stacked along the trench, it should be supported and lifted off the ground to prevent damage to the overburden. When the bottom of the trench is rock, etc., it will damage the overburden, should be in the bottom of the trench cushion a layer of sifted soil or sand.
2. Wide nylon belts shall be used for steel pipe sppenders with epoxy coal asphalt anticorrosion layer, petroleum asphalt coating and polyethylene adhesive tape anticorrosion layer. Steel wire rope or iron chain shall not be used. The pry bar for moving steel pipe should be set with rubber pipe. When trucking, the steel pipes should be padded with straw bags to avoid collision. When the pipe is laid along the edge of the ditch, the seamless steel pipe should be padded to prevent damage to the anticorrosive layer.
Groove group welding
Groove group welding is to weld several seamless steel tubes on the ground beside the trench, using rolling welding, easy to ensure quality, easy to operate, high production efficiency, welded into a pipe section and then into the trench. The length of the pipe section is determined by the pipe diameter and the way to lower the pipe. It should not be too long and cause difficulty in moving. Also can not be down the pipe section bending too large and damage the pipeline and anticorrosive layer. Each pipe section should be 30 ~ 40m long. Since the coal tar enamel coating anticorrosive steel pipe does not allow rolling welding, so, can only be placed in the groove of each steel pipe by fixed welding.
After removing the soil and debris from the inner wall of each seamless steel tube, pair them on the square wood or the opposite support. The main work is matching, finding, spot welding, welding. Special attention should be paid to the staggered spacing of spiral welds or straight welds of stitched steel tubes, which should not be less than 100mm arc length. When spot welding and welding, do not knock seamless steel pipe. Layer welding, welding to a certain extent, turn seamless steel pipe, welding in the best position. After the first layer is welded, the second layer is welded. It is forbidden to weld half of the welding seam, and then rotate the seamless steel pipe to weld the other half of the welding seam.
Before the pipe section of the trench, the application of electric spark leak detector to the pipe section of the anticorrosive layer to carry out a comprehensive inspection, found a leak point in accordance with the relevant regulations immediately carefully repair, repair injury and then electrical spark leak detector inspection, qualified after the trench.
Before leaving work, use temporary plugging board to block both ends of the pipe section to prevent sundries from entering the pipe.
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