Q1: Common methods and quality control points for pipeline welding?
Common welding methods include manual arc welding (SMAW), submerged arc welding (SAW), tungsten inert gas welding (GTAW) and gas shielded arc welding (GMAW). SMAW is highly flexible and suitable for field construction; SAW is highly efficient, but only suitable for factory prefabrication; GTAW is used for thin-walled pipes or high-alloy steel. Quality control needs to focus on welder qualifications (such as API 1104 certification), preheating temperature (to prevent cold cracks), interlayer temperature control and post-weld heat treatment. Non-destructive testing (such as RT/UT) and destructive testing (such as bending tests) are the core means to verify weld quality.
Q2: Application and limitations of directional drilling technology in pipeline construction?
Directional drilling (HDD) is suitable for trenchless paving under obstacles such as rivers and roads, with a maximum borehole diameter of up to 1.5 meters. Its advantage is to reduce surface damage and ecological impact, but the drilling trajectory needs to be precisely controlled (using gyroscope guidance). Limitations include geological conditions (such as special drill bits required for rock layers), pull-back force calculation (to prevent pipeline deformation) and mud ratio (to prevent hole collapse). Geological surveys and tensile simulations are required before construction, and residual mud must be removed with a pipe cleaner after completion.
Q3: What special measures are required for winter construction?
In low-temperature environments, the weld joints must be preheated to above 100°C (carbon steel) or higher (alloy steel) to prevent cold cracks; welding rods must be dried and insulated (such as using portable insulation cylinders). Pipeline materials should avoid low-temperature brittle fracture (select steel grades that pass the Charpy impact test). Concrete piers must be added with antifreeze and covered with insulation. The ambient temperature must be tested before work starts every day, and welding must be suspended when it is below -20°C. In addition, personnel must be equipped with cold-proof equipment and equipment must be replaced with low-temperature lubricants.
Q4: How to avoid stress concentration during pipeline installation?
During the design phase, the pipeline direction must be optimized to reduce sharp bends (recommended bending radius ≥ 5 times the pipe diameter); finite element analysis software must be used to simulate stress distribution. During installation, it is necessary to ensure that the bracket spacing complies with the ASME B31.3 standard (e.g. DN150 pipe spacing ≤4.5 meters). The cold tightening process can compensate for thermal expansion stress, and the spring hanger needs to be accurately adjusted according to the displacement. The weld misalignment must be controlled within 10% of the wall thickness to avoid stress concentration caused by geometric discontinuity.
Q5: What are the standard steps and safety specifications for the pressure test procedure?
The pressure test is divided into strength test (1.5 times the design pressure) and tightness test (1.1 times the pressure), and water is preferred as the medium (gas test requires additional approval). The steps include segmented isolation, exhaust, staged pressure increase (10 minutes of pressure stabilization for each stage) and 24-hour final pressure maintenance. Safety measures include setting up restricted areas, installing pressure relief valves and real-time remote monitoring. After the pressure test, the accumulated water must be drained and dried (especially natural gas pipelines), and the recorded data must comply with GB 50235 specifications.
