Short-term failure modes of pressure vessels

Pressure vessels can experience various failure modes, typically categorized into three types: (1) short-term failure modes, (2) long-term failure modes, and (3) cyclic failure modes. This article focuses on short-term failure modes, which occur suddenly under non-cyclic loading conditions. These modes can include brittle fracture, ductile fracture, joint leakage due to excessive deformation, and elastic or elastoplastic instability (buckling). Each type of short-term failure is outlined below, along with preventive measures.

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1.Brittle Fracture

Brittle fracture is a failure mode where a pressure vessel component fractures without significant plastic deformation under a single loading condition. This type of fracture typically occurs due to material embrittlement, inherent material defects, or the impact of stresses. Brittle fracture can lead to sudden and catastrophic failure of the vessel.

Preventive Measures:

Specify fracture toughness requirements for materials.

Ensure adequate post-weld heat treatment to reduce residual stresses.

Set a minimum temperature for hydrostatic testing to prevent brittle fracture.

2.Ductile Fracture

Ductile fracture involves significant plastic deformation before failure. This mode is often caused by overpressure or uniform corrosion, which reduces the thickness of the vessel wall. The stresses in the material exceed the yield strength and ultimate tensile strength, leading to excessive plastic deformation and eventual rupture. Ductile fractures can also result from local overstrain, leading to cracking or tearing in the affected area.

Preventive Measures:

Establish safety factors for yield strength and tensile strength in material selection.

Monitor and control vessel operating pressures to avoid overpressure scenarios.

3.Joint Leakage Due to Excessive Deformation

This failure mode occurs when excessive deformation at joints, such as flange connections, leads to leakage of the vessel’s internal medium. Joint leakage compromises the functionality of the pressure vessel and can be caused by insufficient bolt preload, gasket loss of resiliency, or inadequate flange stiffness.

Preventive Measures:

Use appropriate sealing gaskets with good recovery properties.

Limit the allowable deformation at joints to prevent leakage.

Ensure proper bolt tightening and flange design to enhance joint integrity.

4.Elastic or Elastoplastic Instability (Buckling)

Instability occurs when compressive stresses on a vessel component lead to a geometric change that cannot be reversed once the load is removed. This can happen when the component’s compressive stress exceeds the critical pressure. Elastic instability depends on the dimensions and material properties of the component, while elastoplastic instability depends on these factors as well as the material’s strength.

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Preventive Measures:

Define safety factors for critical loads in structural design.

Minimize geometric deviations in vessel construction to reduce the risk of instability.

Short-term failure modes in pressure vessels are sudden and potentially dangerous. Preventing these failures requires careful material selection, structural design considerations, and proper operational practices. By implementing preventive measures such as specifying material properties, conducting thorough inspections, and controlling vessel load conditions, the risk of these failure modes can be significantly minimized.

Related articles:

Long-Term failure modes of pressure vessels

Cyclic failure modes of pressure vessels