Pressure vessels are critical equipment widely used in industries such as chemical engineering, petroleum, natural gas, and nuclear power. Their primary function is to withstand and store substances under extreme conditions, such as high pressure, low pressure, or high temperatures. Any defects occurring in the design, manufacture, inspection, or use of pressure vessels can have a significant impact on the equipment's safety and reliability. Therefore, it is essential to strictly adhere to standards and regulations during the design and manufacturing of pressure vessels to ensure that every detail is executed perfectly. This article will analyze common defects in the design and manufacture of pressure vessel, including flange design, material selection, welding quality, design calculation errors, and manufacturing process defects, while proposing improvements aimed at providing engineers with deeper insights and directions for improvement.
Flanges in pressure vessels serve as critical connecting components between various parts, such as the vessel's shell and other equipment like pipes and valves. The rationality of flange design directly affects the vessel's sealing and load-bearing capabilities, especially in high-pressure, high-temperature, or corrosive environments. The performance of the flange is crucial for the safety of the vessel.
Flange Size and Shape Deviations: Flange size, shape, and thickness often have design deviations in actual practice. These problems typically arise from insufficient understanding of the material's mechanical properties, incorrect application of design formulas, or inaccurate calculations. For example, designers may fail to consider the impact of flange thickness or miscalculate the circumferential stress, leading to flange deformation or sealing failure under high pressure. If the flange fails to seal properly, it can cause medium leakage, and in severe cases, lead to vessel rupture.
Stress Concentration: Under high-temperature, high-pressure conditions, stress concentration can occur at the flange, accelerating material fatigue and increasing the risk of material failure. If temperature and pressure fluctuations are not adequately considered during design, flanges may experience cracking or leakage over time, especially under extreme operating conditions.
Neglect of Temperature and Pressure Fluctuations: Pressure vessels often undergo temperature and pressure fluctuations during operation. If these factors are not considered in flange design, it may lead to flange deformation and an increased risk of sealing failure over the long term. Therefore, designers must account for temperature and pressure variations in real-world operating conditions to ensure flange stability under extreme conditions.
Flange design should comprehensively consider various operating conditions, including high-pressure, high-temperature environments and temperature and pressure fluctuations. The design should employ precise stress calculation methods, thoroughly considering material properties, thickness, shape, and other factors to ensure that the flange meets strength, sealing, and load-bearing requirements. Particularly in high-temperature, high-pressure environments, flange dimensions and shapes should undergo rigorous calculations and validation to avoid safety risks caused by design deviations.
The structural strength, durability, and stability of pressure vessels are closely related to the materials selected. Proper material selection ensures not only the strength of the vessel but also its reliability under extreme conditions such as high temperatures and pressures. Materials used in pressure vessels must possess sufficient tensile strength, corrosion resistance, wear resistance, and thermal stability to maintain excellent performance during operation.
Use of Substandard Materials: Some enterprises fail to strictly follow relevant standards during material procurement, resulting in the use of substandard materials. For example, materials may fail to meet required strength, corrosion resistance, or brittleness criteria, leading to cracks, corrosion, or brittle fractures under high-temperature and high-pressure conditions. In severe cases, this can cause vessel rupture or leakage, even leading to explosion accidents.
Mismatch Between Material Properties and Operating Conditions: Materials selected for pressure vessels must be precisely chosen according to the actual operating conditions. For example, high-temperature materials should be selected for high-temperature environments, and materials with excellent corrosion resistance should be chosen for acidic or alkaline media environments. Improper material selection not only reduces the vessel's load-bearing capacity but may also cause cracks, corrosion, or brittle fractures during use.
Negligence in Material Procurement and Management: During material procurement, enterprises sometimes fail to rigorously follow standards and specifications, resulting in material quality issues or performance discrepancies due to insufficient supply chain management. Such inconsistencies can directly impact the overall performance and safety of the pressure vessel.
Strict Material Selection and Testing: Pressure vessel materials should be selected based on the specific operating environment, medium properties, and factors such as temperature and pressure. Especially under high-temperature and high-pressure conditions, materials must be carefully selected in accordance with relevant standards to ensure their properties meet design requirements. Additionally, enterprises should enhance quality control during material procurement to ensure that only qualified materials are used.
Regular Testing and Maintenance: After the pressure vessel is put into operation, regular testing of material durability is essential. Especially in highly corrosive environments, periodic corrosion testing should be conducted to identify any potential material degradation issues, allowing for timely repairs or replacements.
Welding is a core process in the manufacturing of pressure vessels, directly affecting the structural integrity and sealing of the vessel. Welding defects not only reduce the strength of the vessel but also pose significant safety risks during operation.
Weld Cracks: Weld cracks are common defects during the welding process, especially under high-temperature and high-pressure conditions. Stress concentration at the weld can lead to localized failure. Weld cracks can weaken the vessel's load-bearing capacity and potentially cause local ruptures, ultimately leading to vessel failure.
Porosity and Slag Inclusion: Porosity and slag inclusion are common welding defects. Porosity occurs when gas fails to escape during welding, leaving small holes, while slag inclusion arises when impurities are not completely removed from the welding area. Both defects can reduce the mechanical properties of the welded area, leading to uneven stress distribution and increasing the risk of failure.
Incomplete Penetration: Incomplete penetration refers to a situation where the weld does not fully bond with the base material, leaving gaps. This defect can cause leakage or rupture under high-pressure conditions, posing a serious safety risk.
Strict Control of Welding Processes: Welding parameters such as heat input and welding speed should be strictly controlled to ensure proper temperature and effective stress management. For pressure vessels operating in high-temperature and high-pressure environments, high-performance welding materials and precision welding processes should be used to minimize defects.
Comprehensive Welding Inspection and Quality Control: After welding, the welds must undergo non-destructive testing, such as X-ray or ultrasonic testing, to detect any potential defects for timely repair. Additionally, welders should be highly skilled and regularly trained to ensure that the welding quality meets design requirements.
Design calculations for pressure vessels involve various complex calculations, such as strength calculations, stiffness calculations, and pressure resistance calculations. Calculation errors can directly impact the safety and performance of the vessel, making precise design calculations crucial.
Strength Calculation Errors: Ignoring factors such as material yield strength and stress concentration effects can lead to improper design that cannot withstand actual operating pressure. Especially when there is a large internal-external pressure difference, calculation errors can lead to deformation or rupture.
Improper Safety Factor Setting: The safety factor is an important parameter in design calculations that accounts for uncertainties. In some designs, the safety factor may be set too low, reducing the vessel's actual safety margin. A low safety factor increases the likelihood of failure under extreme conditions.
Rigorous Design Calculations and Verification: Detailed calculations and verification must be performed during the design phase to ensure that all parameters, strength, and stiffness meet standard requirements. For pressure vessels used in high-temperature, high-pressure, or corrosive environments, design calculations should be performed with extra caution to avoid potential design flaws.
Use of CAE Software for Assisted Design: Modern design can benefit from using Computer-Aided Engineering (CAE) software for simulation and analysis, helping designers perform calculations and verifications more accurately, detect design defects in advance, and reduce the risk of human error.
The manufacturing process directly determines the quality of pressure vessels, including welding processes, heat treatment, surface treatment, etc. Process defects not only affect the external appearance but also compromise the internal integrity and service life of the vessel.
Improper Heat Treatment: Heat treatment is a key process to enhance the strength, hardness, and toughness of pressure vessel materials. Improper heat treatment can result in overheating or annealing, weakening the vessel or increasing brittleness, which raises the risk of failure.
Substandard Surface Treatment: Surface treatment processes, such as sandblasting, polishing, and electroplating, aim to improve corrosion resistance and wear resistance. Substandard surface treatment can lead to corrosion or wear on the vessel surface, shortening its service life.
Optimize Manufacturing Processes: Each manufacturing step should be carefully controlled, especially in critical areas such as welding, heat treatment, and surface treatment, to ensure that process parameters meet requirements and the final product meets quality standards.
Training and Management of Process Personnel: Skilled personnel are essential for effective process control. Manufacturing companies should regularly train process personnel to improve their skills and quality awareness, ensuring the effective implementation of manufacturing processes.
Defects in the design and manufacture of pressure vessels can severely affect their performance and safety, potentially leading to catastrophic consequences. The common defects discussed in this article, such as flange design flaws, material selection issues, welding defects, design calculation errors, and manufacturing process defects, highlight the complex nature of pressure vessel design and manufacturing. By implementing improvements such as precise calculations, strict quality control, and advanced manufacturing processes, engineers can minimize these defects and enhance the reliability and safety of pressure vessels.
