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What are the general requirements for laying gas pipelines? 2004-11-16 \"National Training Materials for Assessing and Certifying Pressure Pipeline Designers\" What are the general requirements for laying gas pipelines? (1) Gas pipelines should be laid underground; in special areas, they may also be laid using embankments or other surface methods. (2) Protective measures shall be taken where the required thickness of backfill cannot be achieved, or where external loads are excessive and external operations may pose a risk to the pipelines. (3) At the end of the gas pipeline where it emerges from the ground and on both sides of the elbows, backfilling should be carried out in layers. (4) When the longitudinal slope of the trench is large, measures should be taken to prevent the backfill soil from sliding down, depending on the properties of the soil. (5) In swamps and areas with a network of waterways, stabilizing measures should be taken for pipes when the soil cover is insufficient to counteract the buoyancy of the pipes. (6) When the gas pipeline is buried in an earth embankment, the depth of the embankment and the width of its top shall be determined based on the terrain, engineering geology, hydrogeology, as well as the type and properties of the soil, and shall comply with the following requirements: 1) The thickness of the soil covering the pipeline within the embankment shall not be less than 0.6 m, and the width of the embankment’s top shall be more than twice the diameter of the pipeline and not less than 0.5 m. 2) The slope gradient of the embankment shall be determined according to the type of soil and the height of the embankment ； 3) When earth embankments prevent the drainage of surface water or groundwater, drainage facilities should be installed. The drainage capacity is designed based on the terrain and runoff volume, in accordance with flood control standards for floods occurring once every 25 years ； And take measures to prevent water flow from eroding the earth embankment ； 4) The backfill soil for the embankment should have similar water permeability ； 5) The vegetation along the surface of the embankment foundation should be completely removed. (7) When the gas pipeline crosses roads or railways, the clear height required shall comply with Table 2. Provisions of 9-2: Road type – Clearance height in meters. Pedestrian roads: 2.2; Railways: 6.0; Highways: 5.5; Electrified railways: 11.0. (8) For elbows used to change the direction of pipelines, the radius of curvature of such elbows must be greater than or equal to 5 times the nominal diameter, and it must also ensure that cleaning or inspection equipment can pass through smoothly. (9) When the gas pipeline is laid elastically, straight pipe sections shall be used to connect the elastically laid pipeline with adjacent reverse elastic bends, as well as between elastic bends and artificial bends ； The length of the straight pipe should not be less than the outer diameter of the pipe, and should also not be less than 500 mm. The radius of curvature for flexibly laid pipes shall meet the strength requirements of the pipes, and shall not be less than 1000 times the outer diameter of the steel pipe. (10) Elbows and bends in gas pipelines shall not have folds or shrimp-bend shapes. The alignment deviation of the pipes shall not exceed 3°C.