P-scan system means projection images scanning. It acquires echoes reflected from the two sizes of weld while probe scanning. General three projection planes are used, two parallel to the surface and the another plane normal to its surface and parallel to the weld. Therefore, defects appear as seen from a top view, from a side view and from a end view respectively. From the three views, the size, depth and position of defect in weld can be calculated and displayed in screen. All echoes (small as well as large) are stores in a disk, so we can carry out a latter analysis with different test sensitivities without another scanning. This is another advantage over other testing methods.

System consists of hardware and software. Among hardware, the probe design and echo acquiring play a key role in this system. after theory analysis, experiment and comparison, we have developed transverse wave angle focused probes with incidence angle of 60 degree. These probes have high resolution and signal to noise ratio than ordinary angle probes to test austenitic welds. Echo acquiring card is plugged in computer's extended slot and works under system software. The convert rate is changeable with highest rate of 50 MHZ, which is high enough to acquire all defect information from echoes. Then through signal processing, the evaluation of welds can be realized.

This imaging system is used to test a certain artificial defect (length of 35 mm) located in the middle of austenitic weld, the test result of defect's length, width and depth are 35.5 mm, 3 mm, 15 mm respectively. The field test results of austenitic welds of 9% Ni steel spheres in Beijing Yanshan Petrochemical Corporation show that this system is effective for austenitic welds testing. the comparison of test results between this system, radiograph and dissection are also presented. The results tell us that the results of this system are about the same as that of radiograph, but this system can also tell us the depth of defects.

This system can not only realize the quantitative testing, but also take advantage to qualitative testing. It can produce a complete instantaneous and easy to read documentation of ultrasonic testing for welds. It can also test automatically as long as automatic scanner is equipped. So it will find a wide application in the in-service testing of austenitic welds.