Causes of Pressure Vessel Failure and Preventive Measures

 
Pressure vessels play a crucial role in modern industry, and their stability directly impacts production safety and economic efficiency. Various factors contribute to pressure vessel failure, including insufficient strength, inadequate stiffness, stability issues, and different forms of corrosion. Understanding these causes and their preventive measures is essential for ensuring proper equipment operation and extending its lifespan.

Insufficient Strength

 
Insufficient strength occurs when the stress points in the pressure vessel exceed the material's yield limit, causing the vessel to transition from elastic to plastic deformation. As the load increases, the plastic zone expands, potentially leading to vessel rupture or loss of load-bearing capacity, especially under high temperature or pressure conditions.

Preventive Measures

 
Material Selection: Choose high-strength materials such as alloy steels, composites, or high-temperature-resistant materials to ensure performance under extreme conditions.
Design Optimization: Conduct stress analysis during the design phase to optimize the structure, ensuring uniform stress distribution and avoiding local stress concentrations. Use advanced tools like finite element analysis to predict and optimize the design.
Manufacturing Processes: Employ high-quality manufacturing processes such as precision welding and heat treatment to minimize material defects and enhance strength.
Regular Inspection: Implement regular inspection and maintenance to detect and repair potential structural defects early, preventing minor issues from escalating into major failures.

Inadequate Stiffness

 
Inadequate stiffness refers to the loss of normal operational capacity of the vessel or its components due to excessive elastic deformation. This issue is common in sealing structures and heat exchangers, especially under high temperature or pressure conditions, leading to seal failure or reduced heat exchange efficiency.

Preventive Measures

 
Design Improvement: Enhance structural stiffness by adding support structures or using reinforced designs to minimize elastic deformation. Consider using beams, brackets, or reinforcing ribs in the design.
Material Selection: Use high-stiffness materials such as hard alloys or reinforced plastics, or modify existing materials to improve stiffness.
Manufacturing Precision: Improve machining accuracy to ensure components meet design specifications and enhance overall stiffness.
Operating Conditions: Optimize operational conditions to prevent usage outside the design parameters.

Stability Issues

 
Stability issues occur when external loads or pressures cause the vessel to transition from a stable equilibrium state to an unstable state. This is common in long and slender vessels, particularly under conditions of significant internal and external pressure differentials, which can lead to buckling or deformation.

Preventive Measures

 
Stability Analysis: Perform detailed stability analysis during the design phase to ensure the vessel remains stable under expected loads. Use stability analysis tools such as buckling analysis and nonlinear analysis to predict and address stability issues.
Design Improvement: Reinforce the vessel's design by adding support points or improving shape design to enhance stability.
Material Enhancement: Select materials with high stability, such as high-strength alloys or composites, to improve structural stability.
Operational Control: Monitor and control operational conditions to avoid overloading or uneven loads affecting vessel stability.

Corrosion Issues

 
Corrosion is a significant factor in pressure vessel failure and includes various types. Below are common corrosion phenomena and their preventive measures.

1. Stress Corrosion

 
Issue Description: Stress corrosion occurs when materials corrode under tensile stress in specific media, leading to equipment failure. It typically develops over time, causing material performance deterioration.
Preventive Measures: Use materials resistant to stress corrosion, employ corrosion inhibitors or protective coatings, implement anodic protection, reduce or eliminate stress concentrations, improve material stress states, and conduct regular inspections and maintenance.

2. Hydrogen Embrittlement

 
Issue Description: Hydrogen accumulation in metals reduces material ductility, leading to hydrogen embrittlement, which manifests as increased brittleness, cracks, and fractures.
Preventive Measures: Select materials with low hydrogen embrittlement sensitivity, minimize hydrogen environments using inhibitors or protective coatings, and employ surface treatment techniques (such as shot peening) to increase residual compressive stress in materials.

3. Steam Corrosion

 
Issue Description: At high temperatures, steam can cause oxidation and hydrogen embrittlement of metals.
Preventive Measures: Use materials resistant to high-temperature steam corrosion, such as high-temperature alloys or nickel-based alloys, and perform regular inspections to address any damage from steam corrosion.

4. Alkali Embrittlement

 
Issue Description: High concentrations of alkalis can cause stress corrosion, impacting material durability.
Preventive Measures: Use materials insensitive to alkali corrosion or consider alkali corrosion impacts in design. Employ protective coatings or inhibitors and optimize operating conditions to reduce alkali corrosion risk.

5. Sulfur Corrosion

 
Issue Description: The presence of sulfur can cause various forms of corrosion, such as high-temperature and low-temperature sulfur corrosion, potentially damaging equipment materials.
Preventive Measures: Surface-treat steel with aluminum or add chromium to alloy steels to improve sulfur corrosion resistance. Use sulfur-resistant materials and perform regular inspections and maintenance.

6. Vanadium Corrosion

 
Issue Description: Vanadium oxides produced during combustion can accelerate metal corrosion at high temperatures.
Preventive Measures: Add corrosion-resistant additives to materials, use vanadium-resistant materials, or apply coatings to protect metal surfaces.

7. Irradiation Embrittlement

 
Issue Description: In nuclear technology, materials become embrittled due to exposure to high-energy particle radiation, resulting in volume expansion and increased strength.
Preventive Measures: Choose radiation-resistant materials, conduct radiation resistance testing, implement appropriate radiation shielding, and perform regular inspections and maintenance.

8. Liquid Metal Embrittlement

 
Issue Description: Contact between solid metals and liquid metals can decrease the plasticity or strength of solid metals.
Preventive Measures: Use materials insensitive to liquid metal interactions or add protective layers to solid metals to prevent embrittlement. Conduct regular inspections and maintenance to ensure material integrity.
 
The causes of pressure vessel failure are complex and involve structural, material, and environmental factors. By implementing reasonable design optimization, material selection, manufacturing process control, and regular maintenance, the risk of pressure vessel failure can be effectively reduced. Continuous monitoring of equipment performance and maintenance, along with scientific and reasonable preventive measures, will enhance the reliability and lifespan of pressure vessels, ensuring production safety and stability.