Abstract: In the bundled pipeline, the main pipeline was applied to transfer the offshore oil & gas, while the piggy pipeline was applied to transfer the chemicals. The O.D of the main pipeline was from 6 to 12 inch normally, and the O.D of the piggy pipeline is 2 inch. For the main pipeline, the priority inspection method was automated ultrasonic testing method (AUT), while for the piggy pipeline, the AUT method cannot be used due to the limitation of AUT scanner. If RT method which was not only of low efficiency, but also of high safety risk, was used, it would slow down the laying efficiency of pipe-laying. In order to solve the problem, the article states the research of the phased array UT technique, and designs a new scheme for the 2 inch piggy pipe, and performs the inspection and data analysis of the 35 defective welds (O.D 2 inch, W.T 6.4 mm) (105 induced defects in total). And then, the probability of detection and height sizing accuracy of the defects in all zones of the 2 inch piggy pipe can be evaluated.