The Method of Fatigue Life Calculation

Fatigue analysis is mainly the structural analysis of the systems’ failure tendons when subjected to cyclic loads. Different software is available to study fatigue behaviour as per the cyclic load. Fatigue is the progressive and localised structural damage that occurs when the material is subjected to cyclic loading. Continuous cyclic of high-stress concentrations might cause a crack that propagates and results in leakages.

Fatigue analysis is performed to understand the satisfactory performance level of a structural member under cyclic loading. It understands the member’s performance under all the stages of fatigue failure. It means fatigue analysis gives data related to crack initiation, propagation, and failure probability for the chosen material.

Different types of fatigue analysis methods:

Although there are multiple types of fatigue method analysis available, here we have stated some of the most prominent methods of fatigue life calculations, which are easy to use:

Under the fatigue life, equation fatigue analysis is performed using two methods. It includes the stress life method of fatigue analysis and the local strain method of fatigue analysis. The stress life method of fatigue analysis is pretty popular in the piping industry.

Reasons for fatigue analysis of piping system

Once you understand the fatigue life equation, you must also understand the reasons for fatigue analysis of the piping system. The piping system would be subjected to cyclic loading from different sources. It is always good to perform fatigue analysis during the design stage. For the piping system, the cyclic loading is mainly due to thermal expansion and contraction vibration due to occasional load in motion waves and flow-induced vibration.

Characteristics of low cycle fatigue

It is characterised by high loads and short cycles before failure.

The failure here occurs only with the stress levels featuring the plastic range, including the significant plastic strain which occurs during every cycle. The stresses which will be causing fatigue failure in the piping are the peak stresses.

Fatigue analysis theory and failure criteria

The strains obtained in the test are multiplied by 1/2 of the elastic modules to get the stress amplitude while preparing the fatigue curves. The pseudo stress would be compared with the stress calculated on the assumption of the elastic behaviour of the piping.


Hence, the fatigue life calculation method is easy only if someone understands the above calculations. It is also important to first try and understand the concept properly and then continue with the methods of fatigue life calculation. Once there is crystal clear clarity of concept, then the whole process becomes much easier to follow.

It is important that all materials go through their fatigue calculation of life, as that helps in assisting the quality over anything else.

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