High-pressure pipelines refer to specialized equipment and pipelines used in production and daily life, which may pose risks such as explosion or poisoning. The welding of high-pressure pipelines is a critical process that directly affects the safety performance and service life of the pipelines. Therefore, the welding of high-pressure pipelines must adhere to relevant standards and specifications, employ reasonable welding methods and process parameters, and ensure the quality and integrity of the welds.
This article will introduce the relevant standards and specifications for high-pressure pipeline welding, as well as the basic requirements and considerations for welding processes.
I. Relevant Standards and Specifications for High Pressure Pipeline Welding
The relevant standards and specifications for high-pressure pipeline welding mainly include the following:
GB/T 20801.1-2020 "Technical Specifications for Pressure Piping Engineering Part 1: General": This standard specifies the basic requirements for pressure piping engineering, including design, manufacturing, installation, inspection, testing, operation, maintenance, alteration, and decommissioning.
GB/T 31032-2014 "Welding and Acceptance of Steel Pipelines": This standard specifies welding methods, welding procedure qualification, welding quality control, weld inspection, handling of welding defects, and welding records for steel pipelines.
GB/T 50184-2019 "Technical Specifications for Hydraulic System Pipeline Installation Engineering": This standard specifies the design, materials, fabrication, installation, inspection, testing, and acceptance criteria for hydraulic system pipeline installation engineering.
GB 5044-2019 "Classification of Occupational Exposure to Hazardous Substances": This standard specifies the classification method and criteria for occupational exposure to hazardous substances, as well as corresponding protective measures and detection methods.
GB 5016-2019 "Design Specification for Fire Protection in Petrochemical Enterprises": This standard specifies the basic principles, fire zones, fire separations, fire and explosion prevention, fire facilities, and fire management for fire protection design in petrochemical enterprises.
The above standards and specifications are the main basis for high-pressure pipeline welding. Welders and management personnel should be familiar with and master their contents, and execute according to their requirements.
II. Basic Requirements for High Pressure Pipeline Welding
The basic requirements for high-pressure pipeline welding mainly include the following aspects:
1）Welders: Welders for high-pressure pipelines must pass the examination according to the "Boiler Pressure Vessel Welder Examination Rules" and obtain a welder qualification certificate before being qualified to perform welding work within the validity period. Welders should weld according to the welding procedure specification or welding procedure card and keep welding records. Manufacturing units should establish welder technical files, inspectors should inspect the actual welding process parameters, and keep records.
2）Welding materials: Welding materials for high-pressure pipelines should meet the requirements of design and standards, including pipes, fittings, flanges, welding rods, welding wires, fluxes, etc. Welding materials should have factory certificates of conformity or inspection reports and should be accepted, stored, and used according to regulations. The model, specifications, brand, and batch number of welding materials should be consistent with the welding procedure qualification, and random replacement or mixing is not allowed.
3）Welding methods: Welding methods for high-pressure pipelines should be selected based on factors such as material, thickness, diameter, operating conditions, and position of the pipeline. Common welding methods include manual arc welding, gas shielded welding, submerged arc welding, and argon arc welding. Welding methods should meet the requirements of welding procedure qualification, and arbitrary changes or mixing are not allowed. The selection of welding methods should consider factors such as welding quality, efficiency, cost, and safety, choosing the most suitable welding method.
4）Welding process: The welding process for high-pressure pipelines refers to the specific operation process and parameters of welding, including welding position, welding direction, welding sequence, groove form, welding layers, welding current, voltage, speed, polarity, shielding gas, preheating temperature, post-weld heat treatment temperature, gap, misalignment, etc. The welding process should be determined based on the results of welding procedure qualification and should not be arbitrarily changed or exceed the specified range. The determination of welding process should consider factors such as mechanical properties, corrosion resistance, and deformation control of welds, selecting the optimal welding process.
5）Welding quality control: During the welding process, effective supervision and management should be carried out for welding materials, welding equipment, welding parameters, welding environment, and welding operations to ensure that the welding quality meets the design requirements and standard specifications. Welding quality control should follow the provisions of welding procedure specification or welding procedure card, implementing procedures such as pre-weld preparation, in-process inspection, and post-weld treatment, keeping welding records and welding traceability.
6）Welding inspection: Inspection and evaluation of the appearance, dimensions, shape, defects, mechanical properties, corrosion resistance, etc., of welded joints to determine whether the welding quality is qualified. Welding inspection should be carried out according to the requirements of standards such as GB/T 31032-2014 or GB/T 20801.1-2020, using appropriate inspection methods and equipment such as visual inspection, dimensional measurement, non-destructive testing, mechanical testing, metallographic analysis, etc., to grade and accept welded joints.
III. Considerations for High Pressure Pipeline Welding
High-pressure pipeline welding is a technically demanding task that requires attention to several aspects:
Select appropriate welding methods, electrodes, welding machines, and nozzles, adjust the appropriate current, voltage, and welding speed according to the material, diameter, wall thickness, and position of the pipeline.
Conduct proper groove processing of the pipeline, ensuring that the form, dimensions, and gap of the groove meet the standard, removing oxides, oil stains, and impurities from the groove to avoid affecting the quality of the weld.
When aligning the pipeline, ensure that the centerline and outer wall of the pipeline are aligned, fix the joints with spot welding, ensure that the spot welding positions are evenly symmetrical, the thickness of the spot welding is consistent with the first layer of weld, and the root penetration is achieved.
During welding, adopt a multi-layer welding approach, remove slag and spatter from each layer of weld, stagger the arc initiation and termination points for each layer, ensure the weld is uniform and full, free from defects such as porosity, cracks, and lack of fusion.
During welding, pay attention to heating methods and ranges to ensure uniform heating of the joint, avoid local overheating or overcooling, which may lead to stress concentration or loss of filler material. After welding, conduct tempering treatment to reduce the internal stress of the weld and improve the toughness of the weld.
During welding, pay attention to safety protection to avoid accidents such as electric shock, fire, and burns. Use dry welding rods to prevent moisture or rust, use wind shields to prevent wind interference with welding quality.
If selecting vertical welding for pipeline welding, carefully read Pipeline Vertical Welding Methods Basics and Precautions.
High-pressure pipeline welding is a highly technical task, and the welding quality directly affects the safety performance and service life of the pipeline. Therefore, high-pressure pipeline welding must adhere to relevant national standards and specifications, strictly control technical requirements such as welding materials, welding methods, welding procedure qualification, welding quality control, and welding inspection, to ensure the strength, toughness, and corrosion resistance of the welded joints, prevent the occurrence and expansion of welding defects, and improve welding efficiency and economy. The continuous development and improvement of high-pressure pipeline welding technology will provide strong technical support for the development of China's energy, chemical, petroleum, and natural gas industries.
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