How to detect internal cracks from the outside

The original poster read Article 29. Ultrasound, acoustic emission, endoscopy and other tests can be used.

Or put it this way, the relatively small internal cracks are less than 0.5mm. If there is no special preparation and processing of the surface of the object to be inspected, using an endoscope is simply versatile.； Ultrasound and acoustic emission are used. Although I have never used them, based on the introduction of the equipment, I estimate that there are many influencing factors, and it is extremely inaccurate to judge such a small crack. I wonder if there are professional inspectors out there who can detect small cracks from the outside. Which of the current inspection methods is the best?

There is no problem with ultrasonic testing, but I don’t understand acoustic emission. Endoscopes are not useful at all for small defects.

I have never seen ultrasonic testing, so I don’t know how small cracks on the inner wall can be detected.

(1) Radiographic detection Radiographic detection technology is generally used to detect defects such as pores, dense pores, slag inclusions, lack of fusion, and lack of penetration in welds and castings. In addition, for pressure vessels that cannot be entered by the human body, as well as multi-layer wrapped pressure vessels and spherical pressure vessels that cannot be detected by ultrasonic testing, isotopes such as Ir or Se are often used for gamma ray photography. However, radiographic testing is not suitable for testing forgings, pipes, and bars. (2) Ultrasonic testing Ultrasonic testing (UT) is a non-destructive testing method that uses the properties of attenuation when ultrasonic waves propagate in the medium and reflection when encountering the interface to detect defects. (3) Magnetic Particle Testing Magnetic Particle Testing (MT) is a non-destructive testing method that displays surface and near-surface defects of ferromagnetic materials based on the interaction between the leakage magnetic field at the defect and magnetic particles. (4) Penetrant Testing Penetrant Testing (PT) is based on capillary phenomena to reveal surface opening defects of non-porous solid materials. The method is to infiltrate liquid penetrant into the surface opening defects of the workpiece, use a remover to remove excess penetrant, and then use a developer to show the defects. (5) Acoustic emission detection Acoustic emission (AE) refers to the phenomenon in which materials or structures are deformed or broken by external or internal forces, and strain energy is released in the form of elastic waves. Elastic waves can reflect some properties of materials. Acoustic emission testing is a new non-destructive testing method that determines the degree of damage to the internal structure of the container by detecting the stress waves emitted inside the material when it is stressed. (6) Magnetic memory detection The magnetic memory (Metalmagnetic memory, MMM) detection method is a non-destructive detection method that infers the stress concentration area by measuring the magnetization state of the component. Its essence is a magnetic flux leakage detection method. During operation, pressure vessels are affected by factors such as medium, pressure, and temperature, and are prone to stress corrosion cracking, fatigue cracking, and induced cracking in areas with severe stress concentration. Creep damage is also prone to occur on high-temperature equipment. The magnetic memory detection method is used to find high stress concentration parts in pressure vessels. It uses a magnetic memory detector to quickly scan the pressure vessel welds to find the stress peak parts on the welds. Then, these parts are subjected to surface magnetic particle testing, internal ultrasonic testing, hardness testing or metallographic structure analysis to discover possible surface cracks, internal cracks or material microscopic damage.

Radiation testing, X-ray photography testing, etc.

Use radiographic flaw detection, ultrasonic, TOFD

This post was last edited by Binocchio on 2016-11-10 08:35. The following is an excerpt from NB/T 47013.1—2015 5.1.4 Non-destructive testing methods that can detect defects at any location in the material include radiographic testing, ultrasonic testing, diffraction time-of-flight ultrasonic testing and X-ray digital imaging testing. Generally speaking, the detection capabilities of ultrasonic testing and diffraction transit time ultrasonic testing for surface opening defects or near-surface defects are lower than those of magnetic particle testing, penetrant testing or eddy current testing. 5.1.5 In order to determine the intensity and approximate location of active defects inside or on the surface of pressure-bearing equipment, acoustic emission testing can be used. Acoustic emission testing requires pressure testing of pressure-bearing equipment. When active defects are found, other non-destructive testing methods should be used for re-inspection. Ultrasonic testing can be performed on one side, but the effect is worse than magnetic powder and penetration. Acoustic emission testing can detect the intensity and approximate location of defects on the surface, but other methods are still needed for re-inspection. For cases where the inner surface quality can only be inspected from the outside, it can only be used to confirm that no defects exist. For small-diameter cylinders without internal parts, radiographic inspection or X-ray digital imaging inspection should also be feasible. For radiographic inspection of boiler pipe joint joints, both the film and the radioactive source can be placed on the outside (double-wall imaging).

Ultrasonic rays can be used. In addition, the "Periodic Inspection Rules for Pressure Vessels (TSG R7001-2013)" has been discontinued and replaced by large-capacity gauges.