This study presents that the methodology of fatigue evaluation of small bore connection (SBC), which includes strain measurement, stress calculation, and life estimation. This methodology was used in actual fields and has been confirmed to be so practical that it satisfies the following conditions.

A. Multiaxial dynamic strains required for the calculation of the combined stresses can be measured.

B. The fatigue life prediction can be calculated from the measurement data. Specifically, the most critical accumulated fatigue damage value and direction are calculated by repeatedly extracting a stress-time history and counting cycles.

C. Either in bending or torsional stress dominant vibration, or in different size piping vibration, the same spread sheet can be used to calculate the dynamic stress and evaluate the fatigue.

D. What is necessary to prepare in advance is a suitable fatigue curve, Young’s modulus, and Poisson’s ratio only. The evaluation can be done by simply pasting the measured strain data obtained in the field into a spreadsheet. There is no need for any other preparation such as model calculation or parameter correlation.

E. The calculation can be done in a short time (less than 6 hours) with relatively inexpensive hardware and software (about $3,000 together).

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