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Common types of cracks in pressure vessels and pipelines

Common types of cracks in pressure vessels and pipelines

Cracks are a common concern in pressure vessels and pipelines, posing risks to their structural integrity and safety. Understanding the types of cracks that can occur is essential for effective maintenance and risk mitigation strategies.

1.Corrosion-Induced Cracks

Stress corrosion cracking is a prevalent type of crack caused by the combined effect of internal and external stresses and corrosive media. Often found in boiler steam pipes and vessel supports, these cracks typically manifest on the exterior of pipelines. Prolonged operation of boiler systems can lead to directional corrosion of internal hot water, especially under certain pressures. When the external pressure on the pipeline surface exceeds its stress limit, it inevitably results in external deformation and cracking.



2.Mechanical Fatigue Cracks

Mechanical fatigue cracks are commonly observed in rotating machinery components such as impellers, blades, and shafts within auxiliary systems of boilers. The formation of these cracks typically involves two stages: the initial accumulation of strain responses leading to the development of long fatigue cracks, followed by the formation of transverse cracks. The formation of mechanical fatigue cracks is closely related to the operating time of boilers and often exhibits noticeable external characteristics.

3.Creep Cracks

Creep-induced cracking occurs due to the prolonged influence of high temperature and stress, resulting in the deformation and structural damage of pressure pipelines. Commonly observed in header heat-affected zones, high-temperature steam pipes, and expansion pipes, creep cracks significantly reduce the safety of pressure pipelines. Creep cracks often have distinct characteristics, with crack directions mainly perpendicular to the maximum tensile stress. The cracks tend to be tortuous, covering large areas, and most primary cracks are located in the middle of the crack zone.

4.Welding Cracks

The majority of pressure vessels and pipelines in China are welded from metal plates, making welding sites susceptible to cracking under pressure. Factors contributing to crack formation include reduced structural strength at high temperatures and the occurrence of thermal cracks after pressure loading. Typically, pressure vessels need to undergo cooling before they can be put into operation. During boiler manufacturing, cooling cracks may also occur, affecting the operational safety of boilers. During welding, hydrogen atoms come into contact with the base structure. As the weld cools, the austenite gradually transforms into iron, causing hydrogen atoms in the pipeline structure to migrate towards the center, forming hydrogen-induced cracks.

Understanding these common types of cracks is crucial for implementing effective inspection, maintenance, and repair strategies to ensure the safety and reliability of pressure vessels and pipelines in various industrial applications.