Non-Destructive testing has rewarding future in aerospace applications
DT (Non-Destructive Testing) is useful and applicable to almost every industry whether it is aerospace, pipe manufacturing, pipeline installation, plant/infrastructure construction, chemical, petrochemical plants, industrial manufacturing, shipyards or offshore industry, power generation, automobile industry and what not. It provides safety of operations and quality assurance for the final product/outcome. Here's a closer look at the process.
NDT is a powerful and most cost effective means of detecting flaws in objects without disturbing their operational utility. The best feature of NDT is that it is applicable at every stage of a product’s life cycle whether it is under production, trial of an end-product, or a regular health check-up for operational maintenance. NDT always helps to prevent from future uncertainties in terms of massive accidents related to any industry.
Ultrasonic Phased Array (PA), Guided Wave (GW), Infrared Thermography, Magnetic Flux Leakage (MFL), Digital/Computed Radiography, 3D Computed Tomography (CT), and 3D Scanning are some the emerging NDT methods, which are most significant for various industries such as aerospace & defense, automotive, oil & gas, and power generation among others. NDT has its utility in each phase of a product’s life cycle. Adherence of safety guidelines prescribed by industry experts and authorities during the designing phase of automobiles is a major concern. NDT plays a vital role here. During the preparation of initial outlay of a vehicle’s structure, engineers can make an estimate of probable defects and damages of components by applying various NDT techniques. Inspection of laser welds is very useful in detection of flaws in gas generators of airbags. Wall thickness measurement on cast camshafts, radioscopic test of steering frames, and inspection of overlapped laser welds of car bodies are some of the key techniques that help in assuring the functional efficacy of a vehicle during the designing phase to a greater extent.
During manufacturing of an aircraft various materials and design concepts undergo the testing procedure through NDT. These procedures include development of new test concepts as per the pre-design of the structure followed by qualification and certification testing. Ultrasonic and radiographic inspection for detecting sub-surface flaws and liquid penetrant testing for revealing surface defects are the common methods used in aerospace industry. Also, the guided-wave testing, which is a type of long-range ultrasonic inspection, is applicable to inspect internal defects such corrosion and cracks in gas and fuel pipes assembled in an aircraft structure where the chance of error occurrence is very high and tolerance of such defects is nil.
Over the past couple of years, an advanced NDT method for testing functionality of aircrafts has been practiced with the help of onboard sensors and live satellite feeds. These sensors and satellites are used especially for Engine Health Management (EHM). Rolls Royce (U.K.) introduced the advanced concept of real time and post-flight monitoring of engine’s operations through EHM. The innovative EHM is a hands-on technique of evaluating every minute activity in an aircraft’s engine with the help of sensor systems. These systems work on non-destructive principles (no damage to components while inspection), assess an aircraft’s structural condition in real time, and signal the need for maintenance where and whenever required, to prevent accidents and technical failures. These systems have proved to be a cost effective method of structural health monitoring of aircrafts for airlines. Using these sensor systems, maintenance on prevailing conditions of the aircraft while flying, rather than through fixed schedules and inspection routines, results in reduced downtime and thereby the downtime costs as well.
NDT plays a significant role in infrastructure development and its maintenance. All the civil infrastructures such as railway tracks, bridges, roads, commercial buildings, airports, among others utilize NDT techniques for quality assurance and maintenance procedure frequently. At operational level, in order to check and match the hardened concrete with pre-designed layout, NDT techniques provide an appropriate solution. These inspections are basically done on the basis of various parameters such as density, elasticity modulus and strength, surface hardness & absorption, and size & distance from the surface among others. NDT methods are applicable to both new as well as old structures depending upon the different objectives of testing such as quality control, structural integrity, or the resolution of doubts regarding the quality of the used material and construction components.
Visual inspection is the foremost method of performing quality check over new as well as old structures through experienced personnel. Apart from it, there are various methods that can be used for the same, such as:
- Half-cell electrical potential method, used to detect the corrosion potential of supporting bars and metal structures in concrete
- Schmidt/rebound hammer test, used to evaluate the surface hardness and strength of concrete
- Permeability test and Carbonation depth measurement test, used to measure the moisture or flow of water through the concrete that may cause corrosion in future
- Cover-meter testing, used to measure the distance of supporting metal/steel bars from the surface of the concrete and also to measure the diameter of these bars
- Infrared thermography, used to detect voids, delamination and other variances in concrete and also to detect water entry points in buildings
Technology acts as a catalyst for the progress of any industry in the current scenario, so in the NDT industry. Constant technological upgrades since the time of its evolution made NDT amongst the fastest developing industries globally. Introduction of latest technologies such as 3D scanning and computed tomography have improved the inspection process at a different level altogether.
Following are some of the major factors contributing to the growth of NDT industry in the current market scenario:
Successive technological advancements in the non-destructive testing techniques have given rise to 3D scanning test, which is one of the emerging technology introduced recently. 3D scanning is conducted through different technological base such as white light or structured light and laser scanning technique among others. This test is introduced in order to overcome the shortcomings of traditional tests, so as to improve the quality and reliability of inspection and testing techniques of NDT. There are a few additional advantages of 3D scanning such as, high accuracy in defect detection, faster scanning of difficult shapes, and remote distance applications that make it more feasible and reliable for industries that utilize NDT methods. Due to these advantages of 3D scanning, there are several other technologies that can be replaced such as manual pit measurement, ultrasound technology methods, and conventional lasers. Along with the 3D scanning, the development of software tool to analyze the 3D scan data as per the proper standard to deliver assured results will also be introduced in the near future. These software development will allow combined analysis of multiple NDT techniques (ex: UT with 3D scanning), to produces results that go beyond current regulation requirements.
Computed tomography is another powerful NDT testing method (CT) that marked its presence in the industrial environment. The development of X-ray systems and better detectors stimulated the interest of manufacturing and coordinate metrology in computed tomography. CT is used to quantify the measurement uncertainties. Under this technique sectional images are produced and scanned of the internal body an object. It is majorly used for defect analysis and material identification. However, the current challenges of CT is in the quantification of measurement uncertainty, which is not fully established yet due to multiple factors affecting the traceability of these systems.
Automobile industry is amongst the largest user of computed tomography in recent times. A new advanced multi-scan and multi-sensor computed tomography system for the inspection of large aluminum car bodies is developed and successfully applied. Besides 3D CT and micro 3D CT, the technique includes newly developed extended scan methods that allow to scan small sections inside of large objects up to a size of car bodies. A variety of different scan methods handled by a robot leads to a highly flexible system that is able to provide three dimensional information for objects sizing from 3 mm up to 5000 mm. All the basic joining techniques like welding, gluing and riveting can be inspected non-destructively through computed tomography.
INCREASING DEMAND OF EARTHQUAKE RESISTANT INFRASTRUCTURE
Due to the disastrous earthquake occurrence in past decades, the demand for non-destructive testing to build the earthquake resistant infrastructure has increased phenomenally. In Japan, structures which were constructed during the high economic growth period to support the social infrastructure are about to enter heavy deterioration stage due to aging as well as frequent earthquakes occurring in the region. On the other hand, as construction investment continues to be restricted, investment for maintenance is expected to increase. Under such conditions, innovative maintenance methods need to be established. In order to continue to use heavily aged concrete structures safely and comfortably by minimizing the life cycle cost (LCC), it is crucial to upgrade testing technologies, health diagnosis technology, deterioration prediction technology, and repair and strengthening technology. Therefore, at this point of time NDT is playing a key role for improving the quality of testing methods used in infrastructure development and maintenance, especially in earthquake prone regions across the globe.
FLOATING STORAGE OF CRUDE OIL
Crude oil prices went down in the recent times due to poor economic activities in APAC and the Middle East as well as increased shale oil production in the U.S. This has resulted in increased supply of crude oil, which subsequently dragged down the profits of crude oil producers and suppliers drastically. As a result, the storage of crude oil is increased leading to limited supply across the globe. The floating storage of crude oil is in great demand in the current scenario. Non-destructive testing is being practiced for manufacturing of floating storage vessels in cargo ships to prevent the leakage of fuel into the sea. Various non-destructive testing techniques such as, liquid penetrant testing, magnetic particle testing, and eddy-current testing are used to detect the flaws in cargo vessels, in turn driving the NDT industry significantly.
Non-Destructive Testing has a great significance in marine industry since its evolution. Operations of marine sectors are prone to capture high rate of physical damage, such as corrosion, cracks, and delamination due to constant contact with water for longer time. Marine propellers are among the highly vulnerable parts of a ship that catches physical damage. Since the entire operation of a ship is dependent on propellers, regular inspections and preventive measures are necessary, which is easily done through NDT. With the help of ultrasound tests (UT), one can inspect propellers made of copper-nickel-aluminum-bronze or of any other alloy, of different thickness and detect fissures up to few millimeters length. Moreover, ultrasound mobile scanner inspects the entire activity of propeller. Owing to its multi-positional testing capability, it can be operated at horizontal as well as vertical test position on the propeller. Ultrasound system uses a Synthetic Aperture Focusing Technique (SAFT) to produce 3-D image data that provides a detailed display of extra material on joints and welding-seam defects. Leading player of marine propeller market, Wartsila Corporation (Finland) applies this NDT technique during manufacturing as well the heath check-up operations of their propellers.
ONLINE NDT TRAINING
Although the conventional approaches of NDT are still alive and well practiced, improvement in communication and computing technology has led to a growing interest in online training. There have been some apprehensions about training online due to the lack of hands-on experience.
NDT service companies are now welcoming online training in order to save infrastructure cost. Several web-based NDT training companies, such as the American Institute of Nondestructive Testing, and NDT Classroom, Inc. have sprung up in recent years, which is a further testament to this growing trend toward online training.
EMERGING TECHNOLOGIES IN NDT FOR STUCTUREAL HEALTH MONITORING
Modern Non-destructive Testing & Evaluation (NDT & E) methods include various technologies such as Acoustic Emission (AE), Acousto-Ultrasonics (AU), Ultrasonics (UT), Digital Image Correlation (DIC), and Infrared Thermography (IRT). These approaches are primarily used to examine:
- The inspection of the damage in a wide range of modern materials including composites, alloys and smart materials, as well as structural components found in aerospace, marine, oil & gas and transportation industries
- The tracking of deformation and damage across time and length scales by combining traditional NDT methods with modern observational tools ranging from TEM/SEM to optical microscopes
Moreover, damage identification and real-time health monitoring of aerospace structures can be done through various advanced NDT methods. These methods include ultrasonic microscopy and nonlinear acoustics, NDT of micro structured materials by X-ray deflection and refraction topography, use of parametric arrays for low frequency measurements in porous materials that absorb sound, and crack sizing using laser vibrometer measurements through surface acoustic waves. These are some of the crucial methods to inspect flaws in different objects that are evolving the industry and have wide lucrative future.
Non-Destructive testing has a rewarding future as it is applicable to every industry including aerospace & defense, automotive, infrastructure, industrial manufacturing, power generation, and oil & gas. In today’s world where new materials are being developed, older materials and bonding methods are being subjected to higher pressures and loads, NDT ensures that materials can continue to operate to their highest capacity with the assurance that they will not fail within predetermined time limits. NDT can be used to ensure the quality right from raw material stage through fabrication and processing to pre-service and in-service inspection. Apart from ensuring the structural integrity, quality and reliability of components and plants, today NDT finds extensive applications for condition monitoring, residual life assessment, energy audit, and so on. With emerging technologies coming into the market, NDT shows strong growth potential in the coming future.