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Due to the explosive hazards associated with pressure vessels, over the years, Chinese boiler and pressure vessel safety regulatory bodies have enacted a series of regulations along with corresponding product standards. Addressing the characteristics of pressure vessels, technical requirements for materials used in pressure vessels have been stipulated.
Six Considerations for Selecting Pressure Vessel Steels
Considerations 1#
When selecting materials for pressure vessels, the following issues should be considered:
- The working conditions of the vessel, such as temperature, pressure, and medium characteristics.
- The performance of the material, including mechanical, physical, and chemical properties.
- Processing capabilities, such as welding performance and cold/hot working properties.
- Economic feasibility, considering factors like material cost, manufacturing expenses, and service life.
Considerations 2#
Materials for pressure vessels should be selected according to the materials listed in the national standard “Pressure Vessels.” For design pressures not exceeding 35MPa, specific analysis and testing should be conducted for pressures exceeding this limit, followed by research before making decisions.
Considerations 3#
The maximum allowable temperature for steel usage should not exceed the upper limit temperature corresponding to the allowable stress of each steel grade. However, it’s important to note that carbon steel and carbon-manganese steel may exhibit a tendency for graphitization of carbides when used for extended periods above 425°C. For austenitic steels used above 525°C, the carbon content in the steel should not be less than 0.04%. For materials used in low-temperature vessels below -20°C, Charpy V-notch impact tests should also be conducted.
Considerations 4#
The quality and specifications of the steel used for pressure vessel pressure-bearing components should comply with the corresponding national standards, industry standards, and relevant technical requirements. It should be smelted by converter, electric furnace, or oxygen furnace. Steel manufacturers must ensure quality and provide a quality certificate, which should include furnace number, batch number, measured chemical composition, and mechanical properties (values may not be provided for austenitic stainless steels), as well as melting and heat treatment status.
Considerations 5#
Steels used for non-pressure-bearing components of pressure vessels must have good weldability.
Manufacturing Process Requirements: Non-pressure-bearing components typically require welding to assemble into a complete pressure vessel. Therefore, materials must possess good weldability to ensure good weld seam quality and stability during the welding process.- Impact of Welding Performance: The welding performance of materials directly affects the efficiency and quality of the welding process. If the weldability of the material is poor, it may lead to defects during the welding process or insufficient strength of the welded joints, thereby affecting the overall performance and safety of the pressure vessel.
Considerations 6#
While ensuring that pressure vessel pressure-bearing components have sufficient strength, it’s crucial to consider their toughness to prevent brittle failure under external loads.
This is because even if pressure vessel pressure-bearing components have sufficient strength, they may still experience brittle failure under external loads. Strength primarily concerns the material’s load-bearing capacity, while toughness relates to the material’s ability to resist fracture when subjected to impact or strain. During the operation of pressure vessels, they may be subjected to various types of external loads such as impacts or vibrations, which can lead to localized stress concentrations or tiny cracks in the material. If the material lacks sufficient toughness, these cracks may propagate rapidly and result in brittle failure, even if the material’s strength is adequate. Therefore, in addition to strength, toughness is also a critical factor in ensuring the safe operation of pressure vessels and must be considered comprehensively in material design and selection.
Conclusion
The principles outlined above serve as a comprehensive guide for the selection of materials for pressure vessels, ensuring their safety and reliability in various operating conditions.
Understanding Pressure Vessel Materials: FAQs
What are the most common materials used for pressure vessels?
Answer: Common materials include carbon steel, stainless steel (such as 304 and 316), aluminum, nickel alloys, and titanium.
How do you choose the right material for a pressure vessel?
Answer: Consider factors like operating conditions, corrosion resistance, strength, and cost, while adhering to relevant standards and regulations.
What safety concerns should be considered for pressure vessel materials?
Answer: Material strength, corrosion resistance, and reliability are crucial for safety; ensure materials meet standard requirements.
Why is stainless steel commonly used in pressure vessels?
Answer: Stainless steel offers excellent corrosion resistance and high-temperature performance, suitable for various industrial environments.
What are common issues with pressure vessel materials?
Answer: Common problems include corrosion, fatigue, stress corrosion cracking, requiring regular inspection and maintenance.
How does cost impact material selection?
Answer: Cost is a significant factor; balancing material performance and cost-effectiveness is essential in selection.
What is the typical lifespan of pressure vessels?
Answer: Most pressure vessels last 20-30 years, depending on usage and maintenance.
How often should pressure vessels be inspected?
Answer: Regular inspections are crucial, with frequency depending on local regulations and vessel applications.
Can old pressure vessels be retrofitted with new materials?
Answer: While possible, replacing old vessels with modern ones meeting current standards is often more cost-effective.
