Fatigue Failure

Evaluate the total system thoroughly to specify the life of the Expansion Joint in terms of cycles, while preparing the specifications. This is based on different modes of plant operation if the Plant operates at different modes with varying operating conditions, the cyclic requirements based on each operating conditions should be specified. If the specified data is based only on Normal Operating Conditions then any Bellows designer will consider only these data for design. In actual system operation the Bellows Expansion Joints imposed with different modes of varying operating conditions will prematurely fail.

Fatigue Failure

Excess Pressure

  • Do not operate the system at a pressure higher than the specified design pressure.
  • The excessive pressure will cause higher membrane stress resulting in reduced Bellows life.
  • The pressure higher than the specified pressure will lead to Bellows Instability.
  • The Bellows will lose its profile /shape. The results are reduced pressure capability, reduced movement compensating capability and sudden failure

Excessive Pressure 

Excess Movement

  • Ensure that the Bellows Expansion Joints are not imposed with higher thermal movements than the specified value.
  • The higher magnitude of movement than the specified design movement during operation will cause higher bending stresses in the Bellows resulting in pre-mature failure.
  • Evaluate thoroughly for realistic thermal movement of piping and movement of connected equipment etc.
  • Adding arbitrary safety factors will also result in highly flexible joint compromising the stability or result in un-economical design,

Higher Bending Stresses

Improper Shipping & Handling

Dents, gouging, scratches, score marks produced on thin Bellows as a result of improper shipping and handling of Metal Expansion Joints will reduce the life of the Bellows. Though the failure will not happen immediately, the life span of Bellows will get reduced to great extent and failure will be sudden.

Dents, gouging & scratches

Improper Storage

  • Improper storage has led to multiple cases of premature bellows failure
  • High-traffic storage areas expose thin bellows to impacts from hard or sharp objects, leading to physical damage.
  • Preserved bellows absorb condensed atmospheric gases (saline air, SO2), causing corrosion and erosion.

Wrong sleeve direction

During installation, placing the Expansion Joint with its sleeve against the flow direction will result damage of Bellows. The back flow will lead to buckling of sleeve and cause Bellows failure.

Wrong Sleeve Direction

Premature removal of shipping brackets

Do not remove until the completion of installation of anchors, supports and pipe guides. The premature removal of shipping brackets lead to imposing of unwanted huge loads on Bellows resulting in deformation and failure.

Higher Membrane Stress

Insufficient protection of bellows during installation

Arc strikes and weld spatter on Bellows from adjoining weld will damage the Bellows. During installation and till completion of installation cover the Bellows with chloride free fire retardant cloth

Chloride Free Fire Retardant Cloth.

Anchor Failure

Improper anchoring, guiding and supporting of the system can cause expansion Joint failure. Anchor failure in service is another common method of failure..

Erosion Failure

  • The flow medium containing the abrasive particles such as Catalyst, Ores, Slurry etc., should clearly be defined in the specification.
  • The abrasive nature of flow medium will erode the Flow Liner and Bellows which results in failure.
  • A higher thickness sleeve in hardened material will be a solution in applications where the flow medium has abrasive particles.
  • In some cases, a special abrasion resistant lining of inside Expansion Joint will be considered to come out of this problem.

Erosion Failure

Packing of flow medium

  • A flow medium containing dust particles combined with moisture will lead to packing in between the convolutions and the annular space between the Bellows and Liner.
  • The packing will result in improper functioning of Expansion Joint and lead to failure.
  • Insulating the annular space effectively and/or Purging with air/nitrogen in the annular space periodically will prevent the packing/settlement of medium.

Packing of flow medium

Corrosion

Corrosion is the main cause of Bellows failure in several applications having adverse environment and / or adverse flow medium.

(a) External Corrosion

  • In the form of pitting and general metal loss.
  • The saline nature of plant atmosphere and / or gases / pollutants in the atmosphere
    in combination with moisture lead to accumulation on Bellows material resulting corrosion.
  • Presence of chloride will result in stress corrosion cracking on austenitic stainless steel.

External Corrosion

(b) Internal Corrosion

Corrosion mechanisms vary with the pH of the flow medium:
• High pH promotes inter-granular corrosion and cracking.
• Low pH causes trans granular corrosion and cracking.
• In hydrogen service, hydrogen stress cracking often occurs in hardened or aged materials, especially where hardness exceeds 360 BHN, as hydrogen diffuses into these zones and initiates cracks.
• Thin-walled bellows are especially vulnerable when SO₂ gas condenses into H₂SO₄, collecting between the bellows and liner. This accelerates internal corrosion.
• Condensation is typically triggered by:
• Sudden shutdowns,
• Power failures, or
• Exposure to cold external environments.

Corrosion

If you see such failures please contact us immediately.

Email : lsi-mech@lonestarindia.com

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