What About If You Could Hear a Crack Before One Occurred?
Think about if you were next to a steel pipeline that carries thousands of cubic feet of natural gas. Everything looks completely fine from the outside; welds are good, clean surface, normal pressure readings. But within the metal wall, maybe not so much -- a hairline crack is developing very slowly on a micro-scale from thermal cycles.
Now imagine a vibe sensor (or microphone) that collects the acoustic information about that crack (e.g., a very faint ‘stress’ wave) and sends a message to a maintenance engineer that is located three hundred miles away.
That’s not science fiction; it’s an existing technology known as acoustic (or ultrasound) testing which is used today across the globe in oilfields, airplane hangars, nuclear power plants and highway bridges.
This is the hidden science that is keeping everything from collapsing onto itself.
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Ultrasonic Testing: The Science Behind Sound**
Ultrasonic testing uses sound waves as a means to examine the physical properties of a material. To understand this concept, you must first know that sound is a form of wave (a mechanical wave) that exists as a form of disturbance in the form of energy moving through solid, liquid, or gas. Frequency range of sound waves is far beyond what our human ear can detect (the range used for ultrasonic testing is 0.5 MHz - 20 MHz, and for industrial applications). When ultrasonic waves pass through materials they will interact with the structure (makeup) of that material in a variety of ways. The basic principle that underlies ultrasonic testing is as follows:
A piezoelectric transducer converts electrical energy into sonic waves that are then transmitted (directed) into the material being tested. The sonic waves move through the tested metal, composite, or concrete, and when they reach an irregularity (defect, discontinuity), one of three things occurs:
Return (reflected) toward the transducer (pulse echo method)
Attenuate (the wave loses energy as it passes through the defect); or
Scatter (the wave disperses in multiple directions when it encounters irregular boundaries).
By analyzing the time it takes for the signals (waves) to return to the transducer, the amplitude of the signals and frequency of the signals, inspectors can locate the precise position, size and orientation of the defect without physically damaging (scratching the surface) the material being tested.
This is not simply a measurement. It is a means to hear the internal structure of the material being tested.
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The Technology Ecosystem: Sensors and the Cloud**
Acoustic and ultrasonic testing have moved from being tool focused, to being a complete technology ecosystem. Let’s take a look at the entire system on its respective levels.
Sensor Technologies: Detection
There are many things that happen in order to detect something, but everything starts with the sensor. Therefore the type of sensor influences what you can detect, how deep you can see, and the accuracy of how deep you actually can see.
An air attached ultrasonic sensor uses the air as a medium to transmit sound waves. This process makes the air coupled ultrasonic sensor ideal for testing materials that can easily be damaged such as ceramic or composite materials due to the use of coupling gel. Air coupled ultrasonic sensors are also commonly used in the aerospace industry when testing for defects in carbon fibre panels.
Contact ultrasonic transducers provide a highly sensitive measurement of thickness through direct contact with the object being measured or tested, therefore providing a high fidelity signal for both thickness measurement and detection of defects in welds.
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Phased array ultrasonic probes** present one of the most significant advancements in inspection capability to arise in many decades. Unlike traditional inspection methods, a phased array ultrasonic probe contains multiple piezoelectric elements (as opposed to having just one), which can be fired in a precisely timed manner and electronically “steered” without moving the probe. This allows for rapid, volumetric imaging of welds and complex geometry, compared to traditional inspection methods.
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Acoustic Emission (AE) sensors** are unique in their operation; rather than transmitting sound waves into a structure, these devices listen for sounds emitted from the structure itself. Examples of emissions include energy produced by cracks that form, fibers that break, and shifts in weld joints. AE sensors can measure these emissions in real-time, thereby allowing for continuous monitoring of structural health.
Broadband Hydrophones have similar functionality in the underwater environment or in liquids, and provide critical capabilities for inspecting submerged pipelines and offshore structures as well as sonar systems.
The sensor will perform well only if it is operated by a quality system.
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Ultrasonic Thickness Gauges** are essentially the workhorses of the industrial inspection experience. Ultrasonic Thickness Gauges are compact, portable, and measure wall thicknesses from one side only. Ultrasonic Thickness Gauges are essential in monitoring corrosion of pipelines, tanks, and marine hulls, for which access to both sides cannot be provided.
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Ultrasonic Flaw Detectors** provide real-time A-Scan, B-Scan and C-Scan to allow the inspector an opportunity to visualize defect geometry in two and three dimensions. Modern Ultrasonic Flaw Detectors are ruggedized to allow for field use, shock resistant, dust resistant, usable in extreme temperatures, and provide processing capabilities comparable to that of a High End Laptop Computer.
Ultra Sound Systems for inspecting are typically considered Top of the line inspection capabilities. The quality of these systems produces complete cross-sectional images of the welds and components being inspected and will reduce the amount of time spent inspecting by an order of magnitude; for example, a weld that takes hours to inspect can be scanned in minutes Using PAUT (Phased Array Ultrasonic Testing) units.
GWUT (Guided Wave Ultrasonic Testing) provides one of the most unique examples of what ultrasonic technology can accomplish. Low-frequency ultrasound will travel axially within a pipe instead of transversely through the wall of the pipe providing the ability to scan hundreds of meters of pipe from one location and identifying any corrosion or crack that is unlikely to be found by traditional probes.
Acoustic leak detection systems are used to identify the location of leaks in pressurized line systems. These systems work by recognizing the high-frequency acoustic signature created by a fluid escaping from pressurized lines. Acoustic leak detection systems are able to identify leaks even when they are buried beneath ground or are insulated.
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Acoustic Testing in the 21st Century**
The Intelligence Level of the Data/Connectivity Layer Is Where Acoustic Testing is At Its Peak.
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Historically, Non-Destructive Testing (NDT)** was done on an episodic basis, meaning inspectors would arrive on-site, take some measurements, prepare an inspection report and return months or years later to do more inspections. The time between those inspections represents a blind period, in which an approach may not provide any indications of degradation that could have reached a critical level during that blind period.
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The advent of connected and continuous monitoring of acoustics is transforming our approach to acoustic testing.**
Listening for What Matters: A Solution to Finding Defects through Acoustic and Ultrasonic Technology in Industry
Since time immemorial, humans have relied upon our auditory sense to communicate and to determine the ripeness of fruit or the presence of a structure behind a wall or any other unknown object. Acoustic testing has evolved that ancient skill into a precise, scientific method used in current industrial civilization to understand the condition of safety-related materials. This method uses the sense of "listening" about the internal characteristic conditions of commonly used materials we rely on for our safety by carefully and continually observing these materials through acoustic and ultrasonic energy methods of detection.
As we develop the proper infrastructure to support these forms of industrial "deep listening" in the industrial environment, companies such as Acoustic Testing Pro, are necessary to engineer rugged sensors that withstand the elements and will perform in the harshest conditions as well as develop single, cloud-based inspection data management systems that will support inspection data from multi-site enterprises. If the entire world were to be focused on identifying their fault lines as part of a global infrastructure effort, they all would be listening to their faults before they could ever see them.
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