Analysis of Heat Exchanger Accident Types

Heat exchangers play a vital role in many industrial sectors, widely used for thermal energy transfer and fluid control. However, their complex operating environments and various conditions pose potential safety risks during operation. Accidents not only disrupt production but can also lead to severe economic losses and loss of life. This article explores common accident types in heat exchangers, including combustion explosions, severe leaks, and tube bundle failures, analyzing their causes, consequences, and preventive measures. A comprehensive understanding of these safety hazards aims to enhance awareness of safe heat exchanger operation and provide effective improvement suggestions for related fields.

Heat Exchanger Combustion Explosions

Combustion explosion accidents are the most serious type in heat exchangers, often accompanied by significant economic losses and casualties. Their causes involve multiple factors, including equipment design, manufacturing quality, and operating procedures. Improper modifications to homemade heat exchangers can reduce their pressure capacity, while poor welding quality, especially at joints, increases the risk of leaks and fatigue fractures. Key factors leading to combustion explosions include the following.

1. Inadequate Equipment Design

Unreasonable changes in structure and materials can lead to decreased manufacturing quality. Failing to meet pressure vessel standards significantly reduces pressure capacity and increases accident risk.

2. Poor Welding Quality

Incomplete welds without necessary inspections and pressure tests can lead to leaks or fatigue fractures at welded joints. Strict control of welding parameters is essential to ensure quality.

3. Corrosion Issues

Stress corrosion and intergranular corrosion can weaken pressure resistance, potentially causing tube bundle failures or severe leaks, which are explosive when ignited. Early detection and monitoring of corrosion are crucial, achievable through regular inspections and chemical treatments.

4. Improper Leak Testing

Using oxygen or flammable gas for leak testing can lead to physical and chemical explosions. It's important to choose appropriate testing mediums and follow safety protocols.

5. Material Accumulation

Failure to discharge contaminants over time can lead to excessive accumulation of flammable materials (like trichloroamine), particularly under high operating temperatures, resulting in violent explosions. Regular discharge and cleaning operations are vital to prevent flammable buildup.

Severe Heat Exchanger Leaks

Severe leaks are a common safety hazard in heat exchangers, potentially leading to environmental pollution, equipment damage, and injuries. Their occurrence is often related to several factors, including corrosion, temperature fluctuations, and equipment defects. Causes of severe leaks are as follows.

1. Corrosion

The presence of steam droplets, hydrogen sulfide, and carbon dioxide can lead to tube leaks. Monitoring corrosion conditions and performing regular anti-corrosion treatments can effectively reduce leak risks.

2. Frequent Temperature Changes

Frequent starts and stops can cause rapid expansion or contraction of equipment, increasing the risk of leaks at the tube sheet. Careful scheduling of operations can help minimize temperature fluctuations.

3. Manufacturing Defects

Defects in the heat exchanger itself and leaks at welded joints can also lead to severe leaks. Strict adherence to quality standards during manufacturing and comprehensive quality checks before shipment are essential.

4. Increased Operating Temperatures

Higher operating temperatures can cause bolts to stretch, loosening fastening points and leading to flange leaks. Regular checks on fastener conditions and adjustments during significant temperature changes can help prevent this.

5. Mechanical Impact

Loose tube bundle assembly, vibrations, thermal shocks from starts and stops, and improper operations during maintenance can all contribute to leaks. Regular maintenance and careful operation can effectively reduce risks from mechanical impacts.

Heat Exchanger Tube Bundle Failures

Tube bundle failures are one of the weak links in heat exchangers, often leading to reduced efficiency and safety hazards. They manifest as corrosion cracking, collision damage, and flow-induced vibration damage.

1. Corrosion Cracking

Heat exchangers made from carbon steel can suffer from severe oxygen polarization corrosion due to dissolved oxygen in cooling water, with tube bundle lifespans often only a few months to a couple of years. Using corrosion-resistant materials or coatings can significantly extend their lifespan.

2. Fouling

Scaling on the internal and external walls of the tube bundle increases thermal resistance, leading to reduced heat transfer efficiency and potential flow blockages. Regular cleaning and maintenance are essential to ensure smooth fluid flow and maintain efficiency.

3. Induced Vibrations

Increasing shell-side fluid flow rates to enhance heat transfer and reduce fouling can induce vibrations, damaging tubes in the bundle. Optimizing fluid velocities and heat exchanger layouts during design can help mitigate vibration risks.

4. Common Damage Forms

Tube Collisions

Sufficient amplitude in tubes can lead to collisions between them or with the internal walls of the heat exchanger, causing wear and cracking. Using vibration-dampening devices and adjusting tube bundle designs can effectively reduce collision risks.

Repeated Collisions

Radial gaps between baffle holes and tubes can cause repeated collisions, leading to localized damage. Optimizing baffle designs and adjusting tube spacing can help minimize this risk.

Material Defects

Defects in tube materials can cause fluctuating stresses due to vibrations, leading to rapid crack propagation and eventual tube failure. Choosing high-quality materials and regular material inspections can mitigate the impact of material defects on tube bundles.

Flow-Induced Vibration

In areas with significant deflection and high shell-side flow rates (e.g., U-bends, inlet/outlet connections, tube sheets), flow-induced vibrations can lead to tube damage. Enhanced monitoring and control of these areas can help prevent tube bundle failures.

Conclusion

To address safety hazards in heat exchangers, it's essential to strengthen design, manufacturing, and maintenance management, conducting regular repairs and inspections to reduce accident risks and ensure safe, stable operation. Additionally, enhancing employee training and safety awareness is crucial for ensuring that operators fully understand the working principles and potential risks associated with heat exchangers. Through comprehensive measures, the occurrence of heat exchanger accidents can be effectively reduced, improving overall safety.