How to carry out quality control during the installation of process pipelines in chemical plants?

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The last edit to this post was made by sjytangtang on 2019-9-24 at 09:59. If a chemical plant is compared to a person, then the equipment is undoubtedly the \"heart\" of that plant”； Process pipelines that transport raw materials, water, gas, finished products, etc., are the \"arteries\" and play a crucial role in the production process. Therefore, from the outset of the project construction, strict control must be exercised over the quality of process pipeline installation; poor quality will **affect normal production in the future** ； As a chemical construction company, ensuring the quality of process pipeline installation is crucial for the survival of such companies, and it also serves as a guarantee for production units to carry out operations safely in the future. The control of the construction quality of process pipelines must be carried out throughout the entire process, from the preparation stage right through to cleaning and airtightness testing. We can divide the project into the following three phases: During the preparation phase, it is necessary to understand the characteristics of the process construction for this project, identify the difficulties in construction as well as the areas where quality issues are likely to arise. Generally, efforts should be focused on the following aspects: 1. Organizational structure: Establish a quality assurance system, organizational structure, and quality management procedures, clarify the quality responsibilities of various management departments, and assign responsible persons ； Moreover, once the personnel for the project team are assigned, they must not be replaced arbitrarily unless it is absolutely necessary before the project is completed. 2. Technically: It is necessary to thoroughly study the construction drawings, understand the main functions of each device in the system by examining the flow diagrams, and refer to the table of pipeline characteristics to become familiar with the medium, pressure, material, temperature, etc., of all the process pipelines that connect the various devices. For pipelines involving high temperatures, high pressures, special materials, or special media, it is important to identify the key aspects of quality control, thereby establishing the main objectives for quality control in the construction of the project’s process pipelines ； When reviewing the construction plan, clear and reasonable requirements should be set for quality standards, construction methods for key items, and quality assurance measures. 3. Personnel training: Develop welding procedure specifications tailored to the material used in the pipeline design for this project, conduct welding procedure evaluations to ensure compliance with relevant standards, and provide training for welders so that they obtain the necessary welding qualifications for this work. 4. Material procurement: In accordance with the material types, specifications, and standards specified in the material preparation plan, it is necessary to select qualified material suppliers who possess the capability for processing and manufacturing as well as the necessary certifications. Materials must meet relevant requirements upon acceptance ； The quality certificate must be the original version; its contents must correspond to the actual product, and the data provided must be accurate and meet the standard requirements ； Upon arrival at the site, the valves must undergo a hydrostatic test. All alloy steel pipes, fittings, valves, etc. must be rechecked for their chemical composition (through spectral analysis) ； High-pressure pipes, fittings, and valves must be re-inspected 100%. 5. Inspection of welding materials: The external packaging must not be damaged or damp; the markings on the packaging (model, grade, specifications, production date, batch number) must match those indicated in the accompanying quality certification documents. If there is any discrepancy, re-inspection is required to ensure compliance. Before starting the installation process, engineering technicians must provide technical instructions to the construction workers; these instructions mainly cover the construction methods, quality assurance measures, and quality standards ； To ensure the quality of prefabrication, it is possible to avoid the impact of weather and environment on construction, which is beneficial for controlling construction quality. During the installation process, attention should be paid to the following key aspects: 1. Material cutting and processing: It is essential to control the length of the pipes that are cut, the straightness of the cuts, the removal of burrs and edges, as well as the preparation of the grooves ； For pipes with a diameter of DN100mm or less, grinding cutters are generally used for cutting. For large-diameter medium and low-pressure pipes, gas cutting or plasma cutting is typically employed, while the bevels can be prepared using hand-held grinding machines ； High-pressure pipe cutting and groove preparation are generally carried out using a pipe bed or a grooving machine ； Excessive flatness of the cut will affect the uniformity of the alignment gap at the pipe ends. The preparation of the groove should also be carried out at angles specified by the regulations. If the groove is too large, it will lead to waste of labor, materials, and machinery, as well as increased installation costs. On the other hand, if the groove is too small, it can result in welding defects such as incomplete welding and slag inclusions. Therefore, the control of the quality during the material cutting process is aimed primarily at ensuring welding quality and proper installation dimensions. 2. Marking: Each weld joint on prefabricated pipes must be properly marked, especially for pipes made of alloy steel or other special materials. Indicate the welding date, welder’s ID, and weld joint number. Using a schematic diagram, mark the pipeline number and section number on each pipe segment with paint, so as to avoid confusion during installation, prevent the weld joints from being untraceable, avoid discrepancies between the delivery documents and the actual condition of the pipes, and prevent errors in the placement of pipes made of special materials ； The ends of the prefabricated pipe sections must be sealed. 3. Welding: The control of welding quality is the most important aspect in the construction of process pipelines; welders are required to follow the welding procedure manuals strictly ； There are many factors that affect welding quality; in addition to the alignment of the pipe ends and the shape of the groove, it is also influenced by the skill level of the welder, the welding materials, and weather conditions ； Welding is carried out in workshops or on the ground, resulting in minimal environmental impact and relatively easy quality control. The key is to ensure proper baking of welding materials, following strictly the baking and distribution procedures; it is also necessary to control the amount of welding rods taken by welders each time, and to supervise the proper use of welding rod containers ； If the process requires preheating and heat treatment of the welds, it is essential to strictly control the preheating and heat treatment temperatures for each weld. For high-pressure pipe welding, attention must also be paid to non-destructive testing of the quality of the root pass ； 4. Installation: The on-site installation of process pipelines represents a challenge in terms of quality control, as it is influenced by the conditions at the installation site and various environmental factors; appropriate quality assurance measures should be taken when necessary ； The welds made on-site are usually fixed joints, and it is difficult to control their quality; therefore, it is essential to pay attention to the following aspects: during the prefabrication stage, each welder should be monitored and their success rate recorded, as the worker represents the key element in quality control ； The on-site alignment quality of the pipe ends must also be ensured in accordance with the requirements ； In cases of wind, snow, rain, high humidity, or similar weather conditions, effective protective measures must be taken before welding is permitted ； Piercing alloy steel pipes with argon gas is very difficult; therefore, it represents the weakest link in on-site quality control and should also be the most important aspect of quality inspection. Flux-coated or flux-cored wires can be used for root pass welding, but this process must be approved through a welding procedure qualification, and the welders must pass relevant examinations. The quality of construction work can be assessed to a certain extent through inspections. Non-destructive testing, pressure testing, and purging are essential components of the installation of process pipelines; they serve as means to complete the pipeline installation process as well as tools for evaluating the quality of the construction. This requires a certain level of planning and implementation in strict accordance with the specified standards. 1. Non-destructive testing: Non-destructive testing must be carried out strictly in accordance with the specified requirements. Each weld on each pipeline performed by each welder should be sampled for inspection; if any defective welds are found, they must be repaired until they meet the standards, and additional sampling inspections must be conducted until all welds are satisfactory. Otherwise, 100% inspection of that welder’s welds is required ； After heat treatment, the hardness of pipes made of alloy steel should also be measured ； 2. Pressure testing A: Before pressure testing: The pipeline installation work within the testing range has been completed in accordance with the design drawings, except for painting and insulation; the installation quality meets relevant regulations ； The pressure gauges used for testing have been calibrated and are within their periodic inspection period; their accuracy must be at least 1.5 grade. The full scale value of the gauges should be 1.5 to 2 times the maximum pressure to be measured, and there must be no fewer than 2 such gauges ； Once the test pipeline has been isolated from unrelated systems using blind flanges, the safety valves, rupture discs, and instrumentation components on the pipeline have been removed ； Before pressure testing, the air should be completely removed when filling with liquid. B. All pipes that require non-destructive testing must pass the inspection; only after approval by the relevant departments and units can pressure testing be carried out. C. During the hydrostatic test, the ambient temperature should not be lower than 5°C; anti-freezing measures should be taken when the ambient temperature is below 5°C. D. During the pressure testing process: The hydraulic test should involve a gradual increase in pressure. Once the test pressure is reached, it should be maintained for 10 minutes; thereafter, the pressure should be reduced to the design value. The system should then be held at this pressure for 30 minutes. A successful test is indicated by no drop in pressure and no leaks ； For pipes with a large pressure difference, the static pressure of the test medium should be included in the test pressure. E. After pressure testing: the blind flange should be removed promptly, and all liquid should be drained. When draining, negative pressure must be prevented from forming, and the liquid must not be discharged indiscriminately. 3. Purging A. A purging plan must be prepared before purging; the specific methods of purging should be determined based on the requirements for using the pipeline, the working medium, and the degree of dirtiness on the inner surface of the pipeline. Steam pipes should be purged with steam ； Non-thermal pipelines must not be purged with steam. B. For pipes with special requirements, corresponding purging methods must be employed. Equipment and pipelines that are not allowed to be purged should be isolated from the purging system ； The purging sequence should follow the main pipes, branch pipes, and drain pipes in order; the dirt removed during purging must not enter the pipes that have already passed the inspection. C. During flushing, the maximum flow rate should be used, with the flow velocity not falling below 1.5 m/s; the water flushing must be continuous, and it is considered successful when the color and transparency of the water exiting the outlet match those observed in the permeated water. D. Before purging the steam pipes, it is necessary to warm them up, drain water promptly, and check for thermal displacement of the pipes ； The purging sequence should be carried out in a cycle of heating–cooling–reheating. At the same time, the flow rate should not be less than 3 m/s. E. After the pipeline has been successfully purged and restored to its normal state, no other operations that could affect the cleanliness inside the pipeline shall be carried out. In summary, the quality of a project determines its service life; a positive evaluation from a good client can help the construction company build a good reputation in the market, and such a good reputation can open up opportunities for further development. In the context of increasingly fierce market competition, quality will be a crucial factor among many considerations. Only by strictly controlling quality can there be greater development. This article is from the Design Institute website www.shejiyuan.com