Long-Term failure modes of pressure vessels

Pressure vessels are subject to various failure modes, classified into short-term, long-term, and cyclic failures. This article focuses on long-term failure modes, which occur over an extended period under non-cyclic loading. These modes include creep rupture, creep-induced deformation, creep instability, erosion and corrosion, and environmentally assisted cracking. Below is a detailed description of each long-term failure mode, along with preventive measures.

RINA tested EN 10253-2 S355JR pipe fittings

1.Creep Rupture

Creep rupture occurs when metal materials in high-temperature pressure vessels slowly undergo plastic deformation over time, even under loads below the yield strength. This deformation causes a reduction in the cross-sectional area of components, leading to increased stress and eventual rupture.

Preventive Measures:

Select appropriate materials resistant to creep at high temperatures.

Control stress levels to minimize deformation over time.

2.Creep Deformation

Creep deformation refers to the excessive deformation at mechanical joints or components, which can result in the transfer of unacceptable loads. Over time, this deformation weakens the joints or connections, affecting the overall integrity of the vessel.

Preventive Measures:

Use suitable materials designed for high-temperature performance.

Maintain stress levels within safe limits to reduce deformation.

pressure vessel

3.Creep Instability

Creep instability occurs when high-temperature vessels experience buckling or collapse due to creep deformation under compressive stress. As the material deforms under high temperature, the vessel becomes unstable, leading to structural failure.

Preventive Measures:

Choose materials with high creep resistance and thermal stability.

Regulate stress levels to avoid exceeding the critical pressure that leads to instability.

4.Erosion and Corrosion

Erosion and corrosion occur when the vessel’s metal material is gradually worn down by exposure to harsh media, such as corrosive fluids or abrasive particles. This leads to a reduction in wall thickness, lowering the vessel’s load-bearing capacity or causing localized perforation, which may result in leaks.

Preventive Measures:

Use materials compatible with the media inside the vessel to resist erosion and corrosion.

Factor in corrosion or erosion allowances during the design phase to account for material loss over time.

5.Environmentally Assisted Cracking

This failure mode involves cracking of the material due to exposure to corrosive environments, often accompanied by stress. Examples include stress corrosion cracking (SCC) and hydrogen-induced cracking. These types of cracking can significantly compromise the integrity of the pressure vessel over time.

Preventive Measures:

Select materials that are resistant to the specific corrosive media.

Use appropriate manufacturing techniques to reduce residual stress.

Add corrosion inhibitors to the operating environment when necessary.

Long-term failure modes in pressure vessels develop gradually over time, primarily due to high temperatures, corrosive environments, or sustained stress. To prevent such failures, careful selection of materials, control of operating conditions, and routine inspections are essential. By addressing these factors, the risk of long-term failure in pressure vessels can be significantly minimized, ensuring safe and reliable operation over extended periods.