Fatigue of Welded Components

Fatigue of Welded Components

Fatigue is a critical phenomenon that affects the durability and reliability of welded structures. It is the primary cause of failure in welded components, accounting for approximately 90% of failures.

Fatigue occurs when a material is subjected to cyclic or fluctuating stresses, even at levels below the material’s yield strength. Over time, these repeated stress cycles initiate and propagate microscopic cracks, eventually leading to catastrophic failure if left undetected and unmitigated.

Significance of Fatigue in Welded Structures

Welded joints are particularly susceptible to fatigue due to the inherent discontinuities, stress concentrations, and metallurgical changes introduced by the welding process. These factors can significantly reduce the fatigue life of welded components compared to their unwelded counterparts. Fatigue failures in welded structures can have severe consequences, including lost production, costly repairs, and even loss of life.

Factors That Affect Fatigue Strength

Fatigue of welded steel components is often initiated by mechanical vibration, corrosion, and thermal cycling. Factors that influence the fatigue strength of welded joints, include:

• Weld geometry and profile: Sharp transitions, undercuts, and discontinuities at weld toes act as stress raisers, promoting crack initiation and growth.
• Residual stresses: Welding processes introduce residual stresses, which can superimpose with applied stresses and accelerate fatigue crack propagation.
• Metallurgical changes: The heat-affected zone (HAZ) near the weld experiences microstructural changes that can alter material properties and fatigue behavior.
• Environmental factors: Corrosive environments, elevated temperatures, and other service conditions can exacerbate fatigue damage in welded structures.

Understanding these factors is crucial for accurate fatigue life prediction and developing effective design rules and mitigation strategies for welded structures.

O’Donnell Consulting performs API-579 / ASME FFS-1 Fitness-For-Service Evaluations – which is used to Determine the Safety and Financial Risk Factors Related to Component Repair or Replacement.


Bill, Sr. Shares Insight about Managing Risk Specific to Weld Failures in his Article Quantifying Fitness For Service. (PDF)