Ultra-testing of stainless steel plates

This post was last edited by realben on 2010-6-1 14:25. Standard: Appendix N of JB4730.3 – Ultrasonic testing and quality grading of welded butt joints in austenitic stainless steel. Although austenitic stainless steel is not very suitable for ultrasonic testing, it is not entirely unusable. The following excerpts from various posts are provided for reference: Selection of ultrasonic testing conditions for austenitic stainless steel: 1. Waveform: The signal-to-noise ratio and attenuation in ultrasonic flaw detection are related to the wavelength; when the grain size of the material is large and the wavelength is short, the signal-to-noise ratio is low and the attenuation is high. Therefore, in austenitic stainless steel welds, longitudinal wave testing is generally used, as shear waves do not propagate in austenitic welds. 2. Probe angle (K value): The direction of hazardous defects in austenitic welds is usually at an angle to the inspection surface. To effectively detect such hazardous defects in welds, oblique P-wave probes are generally used. Since the welds of austenitic stainless steel consist of columnar grains, the signal-to-noise ratio and attenuation vary depending on the detection direction; therefore, the refraction angle of the longitudinal wave probe must be selected appropriately. Practice has shown that for butt welds, using a longitudinal wave refraction angle of bL=45° results in a high signal-to-noise ratio and low attenuation when detected by a K1 longitudinal wave oblique probe. When the weld is thin, a probe with bL=60° can also be used for inspection, but the sensitivity decreases significantly. 3. Frequency ； When inspecting austenitic stainless steel welds, frequency has a significant impact on attenuation; the higher the frequency, the greater the attenuation and the lower the penetration capacity. Due to the coarse grain structure of austenitic stainless steel welds, it is advisable to use a lower inspection frequency, typically ranging from 0.5 to 2.5 MHz, with 2 MHz proven to be an optimal choice in practice. 4. Selection of calibration blocks and reference blocks: As can be seen from the material properties described in point “1”, austenitic stainless steel, as well as its welds, differ significantly from ordinary steel. Many standards require the use of CSK-IA blocks for distance calibration and CSK-IIA blocks for the distance-amplitude curve. Tests show that significant errors occur; due to the large variations in the longitudinal wave speed of different types of austenitic materials, it is best to use blocks made from the same type of material as that being tested, and to create welds using the same welding method.

What was said upstairs is correct – few people possess the skill of using ultrasound for inspecting stainless steel welds; it’s a challenging task, but it’s not impossible to do

Thank you for the answers from the two people above. I actually knew that ultrasonic testing is possible; I asked the wrong question. What I really wanted to ask is: I’ve never heard that it’s difficult to perform ultrasonic testing on stainless steel plates – only that it’s difficult with welds. Is it because the microscopic structure of stainless steel plates differs from that of welds, or did I misunderstand something?

There’s no such option in Table 2 of JB/T4730.1 for the ultrasonic testing of stainless steel plates; the joints are okay, but it’s not possible to make them very thick~

This post was last edited by zhjun on 2010-6-3 09:52. Austenitic stainless steel welds have bicrystalline grain boundaries and coarse grains, which can significantly affect the attenuation and propagation of ultrasonic waves; therefore, they are not suitable.