What should be paid attention to when installing ventilation pipes in a chemical plant in Suzhou?

Matters needing attention in installation and construction of ventilation pipeline in a chemical plant in Suzhou

The ventilation pipeline of chemical plant undertakes the core functions of conveying process waste gas, controlling dust diffusion and ensuring workshop air safety, and its installation quality is directly related to production safety, environmental protection standards and personnel health. In combination with the climate characteristics in Suzhou (rainy and humid) and the special working conditions of chemical plants (many corrosive media and high flammable and explosive risks), the following matters should be paid special attention to in construction:

First, preliminary preparation: accurately adapt to the chemical working conditions and environment.

The preliminary preparation is the basis of avoiding construction risks and ensuring the compliance of subsequent installation, which needs to be carried out around three cores: working condition adaptation, compliance verification and material selection.

In terms of working conditions and on-site investigation, it is necessary to comprehensively sort out the production process of the chemical plant: make clear the type of conveying medium (such as acid waste gas, organic solvent vapor, dust particles, etc.), temperature (normal temperature or high temperature), concentration and pressure of ventilation pipeline, so as to avoid the deviation of pipeline selection caused by parameter misjudgment. For example, when transporting acid waste gas containing chlorine and sulfur, it is necessary to focus on checking the corrosion resistance of pipelines; When transporting flammable and explosive media (such as ethanol vapor), it is necessary to confirm whether the pipeline has anti-static and explosion-proof capabilities. At the same time, combined with the rainy and humid climate in Suzhou, it is necessary to investigate the humidity and ventilation conditions of the construction site, and whether there is a problem of foundation wetness caused by high groundwater level, and formulate a moisture-proof and drainage plan in advance to avoid accelerated corrosion of pipelines due to environmental wetness in the later period.

Compliance verification can not be ignored, and it is necessary to strictly follow the chemical industry norms and local requirements: on the one hand, check whether the design scheme meets the national standards such as Code for Design of Heating, Ventilation and Air Conditioning in Chemical Industry (GB 50195-2015), Code for Acceptance of Construction Quality of Industrial Metal Pipeline Engineering (GB 50184-2011), and the special regulations of Suzhou Environmental Protection Department on the collection and discharge of chemical waste gas (such as waste gas collection efficiency, waste gas collection efficiency, etc.) On the other hand, special permits (such as hot work permit and confined space permit) required for chemical project construction are required before construction, especially when construction is carried out in the factory area with existing production devices, the safety isolation boundary between the construction area and the production area should be clearly defined with the production department to avoid the risk of cross-operation.

Material selection should focus on "corrosion resistance, safety and adaptability": the material of air duct should be determined according to the characteristics of conveying medium, for example, 316L stainless steel (corrosion resistance is better than ordinary 304 stainless steel), glass fiber reinforced plastic or PPH (polypropylene) pipes are preferred for conveying strongly corrosive waste gas; Heat-resistant steel is required for conveying high-temperature flue gas (temperature > 200℃); If the medium contains dust particles, wear-resistant pipelines with larger wall thickness should be selected to avoid pipeline wear and leakage caused by long-term scouring. In addition, pipe fittings (such as flanges, bolts and gaskets) should be matched with the material of the main pipe, for example, stainless steel pipes should be matched with stainless steel bolts to avoid electrochemical corrosion caused by contact of dissimilar metals; The sealing gasket shall be of the type resistant to medium corrosion (such as tetrafluoroethylene gasket for conveying acid medium and nitrile rubber gasket for conveying organic solvent).

Second, the construction process: strictly control the double defense lines of safety and quality.

During the installation of ventilation pipes in chemical plants, "safety" and "quality" need to be controlled synchronously, focusing on preventing corrosion hazards, sealing defects and safety accidents.

The first is the quality control of welding and connection, which is the key to ensure the tightness and structural strength of pipelines. If stainless steel pipes are welded, it is necessary to continue the core requirements of thin-walled stainless steel welding (such as TIG welding, controlling welding parameters and argon protection). At the same time, in view of the corrosiveness of chemical media, it is necessary to additionally ensure that the weld is free of defects such as porosity, slag inclusion and incomplete penetration, which will become the "breakthrough" of corrosive media, leading to preferential corrosion leakage in the weld area. Passivation should be carried out in time after welding (especially for stainless steel pipes), and the oxide layer on the weld surface should be removed by applying passivation paste to form a corrosion-resistant passivation film; For flange connection, it is necessary to ensure that the bolts are fastened evenly (diagonal fastening method is adopted) to avoid gasket seal failure due to uneven stress, and at the same time, do anti-corrosion treatment (such as winding anti-corrosion tape and applying anti-corrosion paint) at the flange joint to prevent corrosion at the joint due to moisture or medium penetration.

Followed by anti-corrosion and anti-static measures to meet the special working conditions of chemical plants. Before pipeline installation, the surface of the pipe should be pretreated: if the pipe is corroded, it should be completely removed by sandblasting or pickling, and then coated with special anti-corrosion primer; During installation, it is necessary to avoid scratches on the pipeline surface and prevent the scratches from becoming the starting point of corrosion. In view of the humid environment in Suzhou, it is necessary to install anti-corrosion isolation pads (such as rubber pads and plastic pads) at the contact parts between the pipeline support and the pipeline to avoid electrochemical corrosion caused by direct contact between the support and the pipeline. At the same time, the anti-corrosion coating of the support should be checked regularly, and if peeling occurs, it should be repaired in time. If inflammable and explosive media are transported, the pipeline should be grounded in an anti-static way: a grounding electrode should be set every 20-30m, the grounding resistance should be ≤10Ω, and the connection parts between the pipeline and the equipment and the pipeline should be connected with jumper wires (copper braided wires) to ensure that static electricity can be effectively led out and avoid explosion or fire caused by static electricity accumulation.

In addition, it is safe operation control to prevent personal and production safety risks during construction. The management of hot work should be strictly implemented in the construction of chemical plant: before hot work, the inflammable and explosive articles within 5m of the working area should be cleaned, equipped with fire extinguishers, fire blankets and other fire-fighting equipment, and at the same time, special personnel should be arranged for supervision. After hot work, it is necessary to confirm that there is no residual fire before leaving; If pipelines are installed in confined spaces (such as inside equipment and underground pipeline wells), the oxygen content in the space (19.5%-23.5% is qualified) and the concentration of toxic and harmful gases should be detected first, ventilation equipment and emergency rescue equipment should be equipped, and the system of "two-person operation and two-person supervision" should be implemented. In addition, it is necessary to protect the existing equipment and pipelines in the factory during the construction process to avoid medium leakage caused by collision. If it is necessary to cross the existing production pipelines or cable trenches, it is necessary to communicate with the technical department of the factory in advance and formulate a special crossing plan to ensure that the operation of the existing production system will not be affected.

III. Acceptance and Post-guarantee: Ensure long-term stable operation.

After the installation of ventilation pipeline is completed, it needs strict acceptance and post-maintenance to ensure its long-term adaptation to the operation needs of chemical plants.

The acceptance link needs to cover "performance testing" and "compliance verification". In terms of performance testing, firstly, carry out pressure test: for the pipeline conveying waste gas, conduct air tightness test, raise the pressure in the pipeline to 1.05 times of the design pressure, and keep the pressure for 30 minutes. If the pressure drop is ≤0.02MPa and there is no leakage (soapy water can be applied to check the weld and flange interface), the air tightness is qualified; If high-temperature or high-pressure medium is transported, strength test is needed to ensure that the pipeline can withstand the pressure and temperature under the design working conditions. Secondly, the ventilation effect is tested. After the ventilation system is started, whether the concentration of waste gas and dust in the workshop meets the requirements of occupational exposure limits for Hazardous Factors in the Workplace (GBZ 2.1-2019) and whether the concentration of pollutants at the waste gas outlet meets the environmental protection emission standards of Suzhou. If not, the pipeline layout or fan parameters need to be adjusted. In compliance verification, it is necessary to check whether the installation position, slope (for example, the slope of the waste gas pipeline containing condensed water should be not less than 0.005 to avoid the accumulation of condensed water) and grounding resistance of the pipeline meet the design scheme and specification requirements, and at the same time, sort out the construction technical data (such as material certificate, welding record and inspection report) to ensure that the data are complete and traceable.

The later maintenance should be planned according to the climate and chemical conditions in Suzhou. During daily maintenance, it is necessary to regularly (at least once a month) check the corrosion of the pipeline surface, the tightness of the flange interface, and the connection state of the anti-static grounding device. If corrosion spots are found, timely apply anti-corrosion paint, and if leakage is found, immediately stop the machine for maintenance; Every quarter, it is necessary to clean up the dust or scale inside the pipeline (especially the pipeline that transports dust or condensable media) to avoid the increase of system resistance caused by pipeline blockage and affect the ventilation effect. In view of the rainy season in Suzhou, it is necessary to strengthen the inspection of outdoor pipelines, clean up the accumulated water around pipeline supports in time, and prevent the corrosion of supports from affecting the stability of pipelines; Before the rainy season every year, the lightning protection and anti-static devices of pipelines should be tested to ensure that the grounding resistance meets the requirements and avoid safety accidents caused by lightning or static electricity. In addition, it is necessary to establish pipeline maintenance files to record the time, content and problems found in each maintenance, so as to provide a basis for subsequent equipment update or transformation.

Through the above whole process control measures, the safety, compliance and reliability of the installation and construction of ventilation pipes in a chemical plant in Suzhou can be ensured, which not only meets the environmental protection and safety requirements of chemical production, but also adapts to the climate characteristics in Suzhou and ensures the long-term stable operation of the ventilation system.