Modern industry is developing towards high (” “ high temperature, high speed, high load) direction, pressure vessel in three " " operating conditions are often not to the next routine testing cycle, it has defects such as corrosion and cracking occurs so as to cause the serious accident. In order to ensure the safe operation of pressure vessel in use, in addition to conventional NDT methods (such as ultrasound, magnetic powder, penetration, eddy current, X-ray etc.), also produced a number of nondestructive testing of new technology, new method and new instrument, then introduces acoustic emission, magnetic memory, infrared thermal wave, ultrasonic phased array technology laser and microwave nondestructive testing.
Acoustic emission detection
The application of acoustic emission technology in the detection and evaluation of pressure vessel structural integrity can be divided into three aspects: new pressure vessel AE testing and evaluation, monitoring and evaluation in the online launch of pressure vessel AE detection and assessment, the sound pressure vessel. The pressure vessel in the medium temperature and pressure to form cracks, emit energy signal associated with the different sound of a series of cases in which crack crack formation and expanding until, according to these energy signal size to determine whether there are cracks produce and expansion of crack. One of the most important characteristics of acoustic emission testing is to be loaded on the pressure vessel test, loading method is generally used for pressure test of pressure vessel, sometimes directly loaded with the working medium, if in the whole loading process have defects in acoustic emission source location signal generation, judging defect is active vice versa; determine the defect is inactive.
Acoustic emission detection can detect the defects of the advantages, namely the expansion of material fracture and crack, so as to provide the basis for evaluation of the use of safety; remote operation, long-term monitoring equipment allows state and defect expansion device is light. The limitation is that the equipment is expensive, the operator's quality requirement is high, and the interference factors are more in the detection process.
Metal magnetic memory test
Metal magnetic memory testing technology is the stress concentration and fatigue damage of the new nondestructive detection and diagnosis method for detecting material, is a non destructive testing method, its basic principle is to record and analyze the resulting products and equipments in the area of stress concentration in the self magnetic leakage distribution.
Metal magnetic memory testing does not need to be detected special object magnetization and demagnetization, but the use of components in the self magnetization in the magnetic field of the earth, without the need for special surface cleaning, the probe lift off effect is not big, do not need coupling, especially suitable for field use, fast, reliable and high detection sensitivity. This technique can not only detect the pressure vessel should be key parts of stress concentration so as to detect defects, can also cause damage to judge the development according to the actual stress and deformation of the information, no damage detection methods for early detection and diagnosis of the effective pressure vessel defects. But because the metal magnetic memory detection technology is a new type of testing technology, so in the use of instruments and practical applications, many problems need to be solved.
Infrared thermal wave detection
Infrared thermal wave nondestructive testing technology is the formation of infrared image characterization of internal defects in the materials or structure changes through internal or surface infrared emission receiving material due to defects or material inhomogeneity in structure technology. According to the infrared nondestructive testing on the workpiece heating condition and the mode of information processing can be divided into active detection and passive detection of two categories, the former is the use of an external heat source as the excitation source to heat the workpiece, get the temperature distribution in different time on the surface of the workpiece by infrared thermal imager to detect internal material defects; the latter is to detection of defects inside the workpiece by using the temperature distribution of workpiece itself, testing for pressure vessels in operation.
Infrared thermal wave nondestructive testing are mainly used in pressure vessel liner detection and welding process inspection. When the internal temperature pressure vessel insulation layer falls off or crack, will cause the pressure vessel in high temperature state and heat damage, even fatigue damage early, there will be hot spot image, infrared thermal wave nondestructive testing is the use of these fatigue heat spot to determine the vulnerable parts of pressure vessels. So we can determine the subsequent inspection of key. This detection technology is a new detection method, because it has the real-time detection, rapid detection, remote non-destructive detection etc., is particularly suitable for detection in high speed, high temperature and high voltage applications; its limitation is due to experience different detection results obtained different conclusions; this technology is easily affected by some factors such as spurious wave, interface reflection wave interference, easy to cause the error detection, detection of pressure vessel defects.
Ultrasonic phased array technology
Phased array ultrasonic nondestructive testing (ultrasonic phased array technology) is a new technology developed in the field of ultrasonic nondestructive testing in recent years. Ultrasonic phased array technology can produce the same acoustic beam and angle as conventional ultrasound, but it is different from the conventional ultrasonic testing can accurately control the angle and focus size of the beam. The development of ultrasonic phased array technology is limited because of the high complexity of the theory and the high cost of instrument and detection. But in recent years, the ultrasonic phased array technology has been paid more attention to the nondestructive testing industry with its flexible beam deflection and focusing performance.
Some advantages of the ultrasonic phased array technology is flexible operation, accurate defect locating, small operating strength, no radiation, no dirt, fast speed, such as ring weld inspection of pressure vessels only need a simple linear scan can detect all weld, and can detect complex shaped surface or inaccessible parts one side, side scan can also analyze and judge to weld; results are very intuitive but also real-time display, and can print or save in order to achieve long-term preservation of results. The limitation is that the surface roughness of the detector is higher, it is relatively sensitive to the temperature, the equipment is expensive, and the personnel quality is high.
Laser nondestructive testing
The application of laser technology in the field of nondestructive testing began in early 70s, due to the unique properties of the laser itself has, the expanding application in nondestructive testing field, and gradually formed a new non-destructive testing technology, laser holographic laser ultrasound, theSome in the modern NDT technology because of its unique ability and has indisputably become the new member of ndt.
Laser nondestructive detection has the advantages of non-contact detection without coupling agent, can detect complex shaped or inaccessible parts, also can realize the remote excitation and reception, so as to realize the online detection of pressure vessels, so the laser nondestructive detection can be used in nondestructive evaluation of pressure vessels such as high temperature and high pressure under harsh environment. The limitation is that there are some requirements on the surface of the object, which is not sensitive to the depth of the object, the equipment is expensive, and the quality of the personnel is high.
Microwave nondestructive testing
Microwave nondestructive testing technology is in the GHzMHz3300 to a 330 frequency of electromagnetic wave radiation to the measured object, through the analysis of changes, the reflection wave and transmission wave amplitude and phase of the wave pattern changes, through the analysis of the scattering wave, so as to understand the sample in the crack, cracks, porosity the defects such as debonding, layered medium, position and size of inclusions, the uneven degree of internal density composite material technology, microwave nondestructive testing technology according to the detection principle is divided into the reflection wave, transmission wave method and scattering wave method in three categories.
Due to the unique characteristics of microwave itself as its short wavelength, high frequency, through the dielectric material ability, so microwave nondestructive nondestructive scanning and can provide accurate data effectively, the defect can be quantified; especially without special analysis, we can get the real-time three-dimensional the image of the defect area, which can be combined with the &ldquo of the site; all material control ” analysis of common material data. The utility model has the advantages of simple instrument, simple operation, convenient carrying, low cost and no need of coupling agent, and the pollution of the material is avoided. Its limitation is the composite microwave can not penetrate the metal and better electrical properties, so it can only be used for defect detection of metal surface cracks and roughness of the internal defects of the composite structure can not effectively detect.
With the development of social productivity, the application of nondestructive testing technology has also increased. Study on new technology of nondestructive testing of pressure vessels, all senior industry experts at this site “ community ” forum and invited experts together to explore the exchange column