The study of physical bodies through ultrasonic waves began to be introduced at the beginning of the last century. The measuring device is called "ultrasonic flaw detector". Immediately after the discovery, the method gained wide popularity among engineers and people involved in research.
General information about the device
Ultrasound penetrates layers of solid material and can even detect the smallest cracks located in the interior 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 use of units is very wide. For example, the production of metals.
The clear interface of the device provides effective and unified use of the device. The device is distinguished by accuracy, due to which it is possible to obtain a high level result and detect present defects.
Application areas
Ultrasound based 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 area of application of the unit.
- Primary metals in bridge beams, beams, rods, pipe blanks.
- Infrastructure. Bolted joints, rails for trains, metal structures.
- Petrochemical industry. Checking the pipelines of tanks, supporting structures.
- Monitoring of the operation of wheels and shafts of train cars, aircraft chassis, engine suspensions, crane booms, drive shafts, tanks and pressure vessels.
- Production area. Turned welding seams, soldered seams, cast products, endurance control of composite materials.
- Checking materials for parts of aircraft, wind turbines, engines.
The use of flaw detectors abroad
In industry, ultrasonic flaw detectors began to be used in the 50s of the twentieth century. Then the first row of lamp devices was created. Over the past time, extensive experience has been gained with the use of the ultrasound control method.
In European countries, flaw detection has taken a strong position. It accounts for one third of the total inspection of products. It is also noted that, despite the automation of labor, the greatest attention is paid to this method.
This is due to the fact that large volumes of work are carried out at facilities such as nuclear power plants, pipelines for various purposes, metal structures, vehicles, etc. A distinctive feature of all of the above structures is their diversity, which makes it difficult to use automation.
Application of devices in domestic industry
In domestic industry, ultrasound control occupies a leading position. This is evidenced by the number of specialists who are engaged in similar work. For example, from 1994 to 2000, according to the Ural Certification Center, 1,475 flaw detectors were checked. 38% of them became professional specialists in the ultrasound method. Distinctive is that the overwhelming number of workers is based on the control of welds.
The principle of operation of the apparatus
The work of an ultrasonic flaw detector is built on pulsed radiation. The reflected ultrasonic waves are fixed and make it possible to find defects. Short radio waves are altered by means of piezoelectric plates B1-I3. They propagate through a layer of contact liquid through the material in the form of a beam with a transverse direction.
Reflected ultrasonic vibrations have an effect on piezoelectric plates B1 B3. EMF is activated, which becomes stronger, changes and enters the flaw detector alarm.
Basic control methods
There are different control methods. The most common, with high efficiency, include:
- echo method;
- method on a mirror-shadow basis;
- shadow reception.
What does a flaw detector consist of?
What does an ultrasonic flaw detector consist of? The scheme is presented:
- pulse generator ;
- defect detector;
- broadband amplification device;
- a device for temporal equalization of amplitude;
- voltage stabilizer;
- conversion device.
Unit diagram
The electrical circuits of devices such as ultrasonic flaw detectors have sufficient complexity.
The principle of operation of the device can be understood more easily if you carefully familiarize yourself with its structure. How to work with such a device as an ultrasonic flaw detector, the instruction will tell you.
The main units of the device of a modern type operate according to the following principle:
- A generator that generates sounding pulses generates electrical oscillations that excite ultrasonic waves in a transducer.
- The ultrasonic signals reflected from the defect are received by the same (combined circuit or other separate circuit) transducer. The signals are changed into electrical pulses supplied to the input of the amplifier.
- The gain adjustment over time is adjusted by means of a time sensitivity control system (TLC).
- Increased to the desired value, the signal is fed to the input of an electric beam indicator and automatic defect detector (ASD).
- The synchronizing device provides the desired time sequence for the operation of all nodal areas of the device simultaneously with the start of the pulse generator (or with some predetermined delay). It contributes to the start of the operation of the scanning generator of the electro-beam indicator.
- Scanning makes it possible to distinguish by arrival time signals of reflection objects that are located at different distances from the transducer. The synchronizer is also responsible for the control of the VCH and ASD blocks.
- Devices are stuffed with instruments that measure the amplitude and time of arrival of the reflected pulse. The scheme of their inclusion is made in different variations. The measuring device processes the signals received from the amplifier, taking into account the time it takes for the signal to pass from the synchronizing device, and gives digital readings on an electro-beam indicator or a separate display.
Device setup
The tuning of an ultrasonic flaw detector begins with the installation of stable generation in a voltage converter. In this case, the selection of the resistor R39 is carried out. Then the desired repetition rate is obtained (120-150 pulses / s), the resistor R2 is selected.
An amplitude index of 70-80 imp / s is achieved by selecting the V1 dynistor. Then, the capacitors C22 and C26 are selected, which set the limits of change for the rotating motors of resistors R30 and R35 and the duration of the pulses of the single-delay delay (10-25 μs) and the controlled zone (7-45 μs).
Device verification
Ultrasonic flaw detector verification is carried out in various ways:
- The first is the inclusion in the circuit of a special simulating device that emits a test signal. The disadvantage of this device is the interference in the circuit of the device and the inability to check the acoustic unit.
- Also known is a method carried out by simulating echo signals, their radiation into the sample settings. Then, after reception, 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 probe and electric cables connecting the probe to the unit. The disadvantage of such a check is the use of the method only for flaw detectors with continuous emission of ultrasonic vibrations, and signal processing based on the Doppler effect. Such a solution is unacceptable for the control of most modern models of devices 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 sample setup by applying contact fluid to the surface of the sample. In this way, acoustic coupling between the sample and the acoustic unit is ensured . The acoustic unit emits ultrasonic waves to the sample. Echoes reflected from the internal reflector are received in the sample and amplified. There is a temporary selection, which is fed to the indicators of the device. The quality of the unit is judged by the level of response 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 instruments of high quality, one can mention ultrasonic flaw detectors of such manufacturers as OmniScan, Epoch, Sonic, Phasor. And among domestic devices, you should pay attention to the brands UD-2, UD-3, "Bearing", 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 function in a variety of modes, depending on conditions and specific goals. Existence of the wide screen of the light and sound indicator facilitates work with the device.
Foreign manufacturers of ultrasonic flaw detectors produce devices that differ in flexible settings. They have a lightweight durable case, small size. These are not just flaw detectors, but universal devices for the average worker.
For example, the basis of the OmniScan device, which has a rich set of functions, consists of phased arrays. This makes it possible to expand the measurement capabilities and obtain an accurate result.
A wide segment of devices should not perplex 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 in certain conditions.
A universal ultrasonic flaw detector, a device with small dimensions, an apparatus operating at low frequencies, a device equipped with a protective case - such a rich number makes it possible to find a suitable device designed to control 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 it is doubly good.
- Ease of use. The fewer additional settings, the easier it is to work with the device.
- Incomprehensible interface. This is very important, because often without special preparation, a beginner simply cannot understand it. The interface should really be understandable so that there are no problems when you enable this or that option.
- Availability of warranty card and service. Pay attention to suppliers and sellers of equipment.
- The instrument should be suitable for piezoelectric transducers manufactured abroad. The same is important when buying a domestic device.
- A clear, well-laid out operating manual.