"Tee joints" are commonly used in various industries including nuclear reactor systems and many a time they are subjected to fatigue loading during operation. This paper highlights the laboratory investigation carried out using ultrasonic testing on a 400 mm diameter 50 mm thick "Tee junction" which was subjected to fatigue loading. The aim of the experimental study is to validate the design of the Tee joint to withstand the fatigue loading conditions and to determine the number of cycles taken for crack initiation and growth. Ultrasonic testing has been used to detect crack initiation and sizing to establish the crack growth. In the laboratory setup, the two ends of the main pipe were held and the branch pipe was loaded in a cyclic manner. The testing was done in displacement control mode applying 60 tonnes load at a frequency of 0.15 cycles.

Periodical monitoring of the initiation of the crack and the growth of the crack was done using ultrasonic testing. The calibration of the equipment was carried out using a reference standard block having a 1 mm deep, 12 mm long fatigue crack. Ultrasonic flaw detector model ECHOGRAPH 1030 with a 45°, 4 MHz frequency angle beam probe was used for evaluation.

Crack initiation was observed in the bottom bent region of the "Tee joint" after 23, 000 cycles. Dye penetrant inspection has confirmed the presence of multiple surface cracks. The growth of the cracks was monitored for every 5000 cycles upto 40, 000 cycles. Numerous cracks initiated from different regions initially were found to join into a single major crack of 300 mm long and 30 mm deep as the experiment progressed upto 40, 000 cycles.

The study clearly demonstrated the use of ultrasonic testing for fatigue crack detection and for crack growth studies.