Regarding the usage scenarios of RT, UT, MT, PT

RT radiation testing is used to inspect critical areas, such as the cross or T-joints at the major joint seams. However, there are requirements regarding the thickness of the plate; if it is too thick, the rays cannot penetrate it. UT ultrasonic testing covers a wide area of inspection; it is easy to use. However, a drawback is that it can lead to missed detections if not performed carefully, and it is not very sensitive to detecting seams in thin sheets. PT penetrant testing is primarily used to detect surface defects in welds. Easy to use. It’s easy to use. MT magnetic particle testing is primarily used to detect surface defects in welds. Non-destructive testing is now widely used in various industries. In the field of special equipment, there are five conventional methods for non-destructive testing: 1) RT – Radiographic testing: primarily used to detect internal defects in materials or workpieces. 2) UT – Ultrasonic testing: mainly used to detect internal defects in materials or workpieces. 3) MT – Magnetic particle testing: used to detect surface and near-surface defects in ferromagnetic materials. 4) PT – Penetrant testing: used to detect surface openings in materials or workpieces (non-porous materials). 5) ET – Eddy current testing: used to detect surface and near-surface defects in conductive materials. For materials such as castings, carbon steel, or alloy steel, which are ferromagnetic, all methods except ET can be employed; however, the thickness of the workpiece and the locations where defects might occur also need to be taken into consideration. MT is the best method for detecting surface cracks, while RT and UT are more suitable for detecting internal defects in thicker workpieces. If flaw detection is required when grooving the material, PT can be used

Can it be understood that RT/UT are mainly used to detect internal defects in welds, while MT/PT are mainly used to detect surface cracks?

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Therefore, in the acceptance criteria for SH3501, RT Grade II, UT Grade I, MT Grade I, or PT Grade I are adopted. Is there a substitutable relationship between them?

Generally, they cannot be substituted for one another; each type of test has its own characteristics and is more sensitive to specific defects

RT is relatively sensitive to volumetric defects such as pores and inclusions； When the angle between the planar defect and the radiation is inappropriate, the likelihood of missed detection is high ； If the workpiece is too thick, a high-energy radiation source is required, and the detection accuracy will also decrease ； UT is relatively sensitive to linear or planar defects, such as cracks and lack of fusion ； If the workpiece is too thin, it increases the impact on detection accuracy, and it becomes difficult to detect items within the blind area ； UT inspection requires a high level of experience and responsibility from the operators, and it is difficult to keep records of the inspections ； MT is relatively sensitive to surface and near-surface defects, offering high accuracy ； For surface flaw detection of ordinary ferromagnetic materials, MT is preferred ； PT can only detect surface open defects, with relatively low accuracy ； Surface inspection of austenitic stainless steel materials can only be carried out using PT ； For relatively important equipment, the design often requires multiple inspection methods to verify each other, as none of them should be used as a substitute for the others.

For some less important equipment and pipelines, is it sufficient to perform only a simple surface inspection?

It depends on which standards are followed for the installation (maintenance) of these pipelines, and whether those standards specify the inspection methods and proportions to be used. If we set aside the standard specifications and focus solely on the inspection methods, unless it is a material with high cracking sensitivity such as Cr-Mo steel or the welding temperature is too low, surface inspection is not very effective; it can be omitted. However, aside from periodic inspections, surface flaw detection plays a significant role in these inspections, as it is often able to detect crack defects that arise during operation.

TOFD inspection technology is also a type of UT; it has a high detection sensitivity. It is currently commonly used for inspecting the weld seams of spherical tanks, but its drawback is that a significant amount of grinding is required for those weld seams.