The study of physical bodies by means of ultrasonic waves began to be introduced at the beginning of the last century. The measuring device was called "ultrasonic flaw detector". Immediately after its discovery, the method gained wide popularity among engineers and people involved in research.
General information about the device
Ultrasound penetrates through layers of solid material and can fix even the smallest crack located in the inside of an object. The device allows you to determine the defect at a depth of 7-50 mm with an accuracy of ±1 mm.
Ultrasonic flaw detectors have different levels of sensitivity. This indicator is determined by the small size of the defects. The scope of the units is very wide. For example, metal production.
The clear interface of the device ensures efficient and unified use of the device. The device is accurate, thanks to which it is possible to obtain a high level result and detect those present.flaws.
Areas of application of the device
Ultrasonic flaw detection can be applied to almost any building material to detect the presence of hidden cracks, pores, slags and other flaws.
The most common areas include:
- Welding seams. This is the main application of the machine.
- Primary metals in bridge beams, beams, rods, pipe blanks.
- Infrastructure. Bolted connections, train rails, metal structures.
- Petrochemical industry. Checking pipelines of tanks, load-bearing structures.
- Monitoring the operation of wheels and shafts of train cars, aircraft landing gear, engine mounts, crane booms, drive shafts, tanks and pressure vessels.
- Production area. Turned welding seams, brazed seams, castings, endurance testing of composite materials.
- Checking the materials of aircraft parts, wind turbines, engines.
Use of flaw detectors abroad
In industry, ultrasonic flaw detectors began to be used in the 50s of the twentieth century. Then the first series of lamp devices was created. Over the past time, extensive experience has been accumulated in the application of the ultrasonic control method.
In European countries, flaw detection has taken a strong position. It accounts for one third of the total product inspection volume. It was also noted that, despite the automation of labor, this method is given the most attention.
This is due to the fact that large amounts of work are carried out onobjects such as nuclear power plants, pipelines with various purposes, metal structures, means of transport, etc. A distinctive feature of all the above structures is their diversity, which makes it difficult to use automation.
Application of instruments in the domestic industry
In the domestic industry, ultrasonic control occupies a leading position. This is evidenced by the number of specialists who are engaged in such work. For example, from 1994 to 2000, according to the Ural Certification Center, 1,475 flaw detectorists were tested. Of these, 38% became professional specialists in the ultrasound method. It is distinctive that the vast majority of employees are based on the control of welding seams.
How the machine works
The operation of an ultrasonic flaw detector is based on pulsed radiation. Reflected ultrasonic waves are fixed and make it possible to find defects. Short radio waves are changed by means of piezoplates B1-I3. They propagate through the couplant layer through the material in the form of a beam with a transverse direction.
Reflected vibrations of ultrasound have an effect on the piezoelectric plates B1 B3. EMF activation occurs, which becomes stronger, changes and enters the flaw detector signaling device.
Main control methods
There are different methods of control. The most common, highly effective, include:
- echo-way;
- methodon a mirror-shadow basis;
- shadow reception.
What does a flaw detector consist of?
What does an ultrasonic flaw detector consist of? Scheme is presented:
- pulse generator;
- defect indicator;
- broadband amplifying device;
- time amplitude equalization tool;
- voltage stabilizer;
- converting device.
Unit Diagram
Electrical circuits of devices such as ultrasonic flaw detectors are quite complex.
The principle of operation of the device can be understood more easily if you carefully read its structure. How to work with a device such as an ultrasonic flaw detector, the instruction will tell you.
The main units of a modern device operate according to the following principle:
- The probe pulse generator generates electrical vibrations that excite ultrasonic waves in the transducer.
- The ultrasonic signals reflected from the defect are received by the same (combined circuit or another separate circuit) transducer. The signals are changed into electrical impulses that are fed to the input of the amplifier.
- Timing gain control is controlled by a Time Sensitivity Control (TCG) system.
- Increased to the desired value, the signal is inputelectric beam indicator and automatic defect detector (ADD).
- The synchronizing device provides the necessary time sequence for the functioning of all the node areas of the device simultaneously with the start of the pulse generator (or with some given delay). It contributes to the start of the sweep generator of the electrobeam indicator.
- Sweep makes it possible to distinguish by the time of arrival the signals of reflection objects, which are located at different distances from the transducer. The synchronizer is also responsible for controlling the TCG and ASD units.
- The devices are stuffed with devices that measure the amplitude and time of arrival of the reflected pulse. The scheme of their inclusion is produced in different variations. The measuring device processes the signals received from the amplifier, taking into account the signal transit time from the synchronizing device, and gives digital indicators on the electrobeam indicator or on a separate display.
Device setup
Setting up an ultrasonic flaw detector begins with the installation of stable generation in the voltage converter. In this case, the selection of the resistor R39 is carried out. Then the desired repetition rate is obtained (120-150 imp / s), the resistor R2 is selected.
An amplitude indicator of 70-80 imp/s is achieved by selecting a V1 dinistor. Then capacitors C22 and C26 are selected, which set the limits of change with the rotating engines of the resistors R30 and R35 and the duration of the pulses of the delay single vibrators (10-25 μs)and controlled zone (7-45 µs).
Check device
Verification of an ultrasonic flaw detector is performed in various ways:
- The first is to include in the electrical circuit a special simulator that emits a test signal. The disadvantage of this device is interference in the device circuit and the impossibility of checking the acoustic unit.
- The method is also known, which is carried out by simulating echo signals, their emission into the tuning sample. Then, after receiving, the entire electro-acoustic path of the flaw detector is checked. It includes the emitting and receiving parts of the electrical unit of the device, which correspond to the PET and the electrical cables connecting the PET to the unit. The disadvantage of such a check is the use of the method only for flaw detectors with continuous radiation of ultrasonic vibrations, and signal processing based on the Doppler effect. This solution is unacceptable for controlling most modern device models distributed around the world.
- Verification of the ultrasonic flaw detector is carried out in another way. It is based on the fact that the acoustic unit is installed on the tuning sample by applying a contact liquid to the sample surface. Thus, an acoustic connection is provided between the sample and the acoustic unit. The acoustic unit emits ultrasonic waves into the sample. The echoes reflected from the internal reflector are received in the sample and amplified. There is a temporary selection, which is fed todevice indicators. The quality of the unit is judged by the level of operation of the indicators. To implement this method, devices made of metal or organic glass with reflectors located inside are used. Similar devices are used by all leading manufacturers of flaw detectors around the world.
Popular flaw detector models
From a wide list of devices of high quality, ultrasonic flaw detectors from manufacturers such as OmniScan, Epoch, Sonic, Phasor can be noted. And among domestic devices, you should pay attention to the brands UD-2, UD-3, "Peleng", devices of the A1212 series. They are reliable.
Domestic devices of the UD series can be classified as universal, since they not only have a wide range of measurements and technical capabilities, but can also operate in a variety of modes, depending on conditions and specific purposes. The presence of a wide screen light and sound indicator makes it easier to work with the device.
Foreign manufacturers of ultrasonic flaw detectors produce devices with flexible settings. They have a lightweight, durable body, small size. These are not just flaw detectors, but universal devices for an ordinary worker.
For example, the powerful OmniScan is based on phased arrays. This makes it possible to expand the measurement capabilities and get an accurate result.
A wide segment of fixtures is notshould confuse the buyer. After all, the technical characteristics of ultrasonic flaw detectors are different, and each device has its own advantages and is effective when used under certain conditions.
A universal ultrasonic flaw detector, a device with small dimensions, a device operating at low frequencies, a device equipped with a protective case - such a rich range makes it possible to find a suitable device designed to inspect elements from a wide variety of materials.
What to look for when buying?
When buying a device, pay attention to the following indicators:
- Portability of the device. The best indicator is the light weight of the device. If the device is compact, then this is doubly good.
- Ease of use. The fewer additional settings, the easier it is to work with the device.
- Intelligible interface. This is very important, because often, without special training, a beginner simply cannot figure it out. The interface should really be clear so that there are no problems when enabling one or another option.
- Availability of warranty card and service. Be careful with equipment suppliers and sellers.
- The device must be suitable for piezoelectric transducers manufactured abroad. The same is true when buying a domestic device.
- Having a clear, well-written operating manual.
