Radiographic or ultrasonic testing and thickness
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Is there a relationship between the choice of radiographic or ultrasonic inspection method and thickness? In accordance with clause 3.2.10.2.1 of the Great Specification, the selection of non-destructive testing methods is independent of thickness, and they are equivalent under conditions other than those involving non-ferrous metals. According to Table 4-1 and Note 4-1 of the Boiler Code, radiation can be used for testing all thicknesses, whereas ultrasound can only be used for testing thicknesses of 20 mm or more. Clearly, the Boiler Code takes the thickness into account when selecting non-destructive testing methods, whereas the Large Scale Code does not consider thickness. In practical applications, for example when dealing with pressure vessels whose joint thickness is 16 mm, should we use RT or TOFD? What is their sensitivity to defects and what do they focus on? Why is there such a big difference between the Pot Rules and the Big Rules?
This post was last edited by wanlirn on 2019-1-15 17:33. Is the choice between ray testing or ultrasonic testing related to thickness? The topic is a bit too broad! If you have a thorough mastery of these two technologies and not just a superficial understanding, then this is not a problem at all ； If you are not a non-destructive testing specialist, you will have to write a lot for this question, and you won’t be able to understand it anyway ；
Containers still primarily use rt; ut is used less often and usually not on its own. Tofd isn’t very common either these days.
Let’s talk about the radiographic and ultrasonic testing sections of the ‘Large Scale Code’ and the ‘Pressure Vessel Code’. Thank you
Standard NB/T47013.3 specifies that the thickness for plate testing and weld joint testing shall be not less than 6 mm. NB/T47013.2 specifies an upper limit for thickness for radiographic inspection.
For equipment housings with the same 16mm thickness, containers can be inspected using either radiation or ultrasound, whereas boilers can only be inspected using radiation. How should that be understood?
Radiographic and ultrasonic testing each have their advantages and disadvantages. For example, with thicker workpieces, the detection sensitivity of ray inspection decreases, and the costs increase as well. Ultrasonic testing has low sensitivity when used to inspect workpieces with thin thicknesses. Since conventional ultrasonic testing does not leave any tangible evidence of the inspection, and it also requires highly skilled personnel, radiographic testing has always been the preferred method ； Later, with the advent of TOFD, both were placed on an equal footing in the new standards. However, ray inspection is still more commonly used: perhaps this is because there are relatively few companies that possess the personnel and equipment for TOFD.
TOFD testing is chosen; this usually requires external testing, right?
TOFD is just one type of ultrasound; it is more effective for medium-thick plates, and it also needs to be used in combination with surface inspection methods such as magnetic particle testing
It gets complicated if you want to explain it clearly! Simply put, it depends on the validity of the test! But it also has something to do with thickness. For thinner ones, RT is better; for thicker ones, TOFD is better!