How to perform nondestructive testing on stainless steel electric heating coils after welding?

How to perform nondestructive testing after welding stainless steel electric heating rings?
After welding stainless steel electric heating rings, the following nondestructive testing methods can be used to detect welding quality:
Visual inspection
Method: Observe the welding surface directly with the naked eye or with the help of tools such as low-power magnifying glasses.
Detection content: Check whether there are cracks, pores, slag inclusions, unfused, undercuts and other defects on the weld surface, and whether the weld is well formed, such as whether the weld width and excess height meet the requirements.
Penetrant testing
Method: Apply a penetrant containing a color dye or fluorescent agent to the inspected surface to penetrate into the surface opening defect, then remove the excess penetrant, apply a developer, and the penetrant in the defect is adsorbed to the surface to form an enlarged defect display trace, and the defect situation is judged by observing the trace.
Scope of application: Mainly used to detect defects on the surface opening of stainless steel electric heating rings, such as surface cracks, pinholes, etc.
Key points of operation: Before testing, the surface to be tested must be thoroughly cleaned to ensure that there are no impurities such as oil, rust, etc., so that the penetrant can fully penetrate the defects; the operation process must be carried out strictly in accordance with the instructions for use of the penetrant detection agent, and the time and temperature of each step must be controlled.
Magnetic particle detection
Method: When there are defects on the surface or near the surface of the test, a leakage magnetic field will be formed at the defect. When magnetic powder is applied to the surface to be tested, the magnetic powder will be adsorbed by the leakage magnetic field to form magnetic traces, thereby showing the location and shape of the defect.
Scope of application: It is suitable for detecting cracks, inclusions and other defects on the surface and near the surface of stainless steel electric heating rings of ferromagnetic materials.
Key points of operation: Before testing, the surface to be tested needs to be polished, rust-removed, etc. to ensure good contact between the magnetic powder and the surface; according to the shape and size of the workpiece to be tested, select the appropriate magnetization method and magnetic field strength.
Ultrasonic detection
Method: Using the propagation characteristics of ultrasonic waves in materials, when encountering defects, ultrasonic waves will be reflected, refracted and scattered, and the location, size and nature of the defects can be determined by analyzing the signal of the reflected wave.
Scope of application: It can detect cracks, pores, slag inclusions and other defects inside the stainless steel electric heating ring, and has a high sensitivity for detecting internal volume defects.
Operation points: Before testing, apply an appropriate amount of coupling agent, such as vaseline, engine oil, etc., on the surface to be tested to ensure that the ultrasonic wave can be effectively transmitted to the workpiece; select the appropriate probe frequency and model according to the material and thickness of the workpiece.
Radiographic detection
Method: Through the rays penetrating the object to be tested, due to the different degrees of absorption and attenuation of the rays by the defects and the matrix, different black images will be formed on the radiographic film, and the type, location and size of the defects will be judged according to the images.
Scope of application: It can detect various defects inside the stainless steel electric heating ring, such as pores, slag inclusions, incomplete penetration, cracks, etc., and has a good detection effect on volume defects.
Operation points: Radiographic detection requires strict control of parameters such as exposure, focal length, exposure time, etc. to ensure the quality of the film; during the detection process, attention should be paid to the protection of rays to prevent personnel from radiation damage.
In practical applications, one or more nondestructive testing methods are usually selected in combination according to the specific structure, material, welding process and detection purpose of the stainless steel electric heating ring to comprehensively and accurately detect welding defects.