PIPELINE INSPECTION

In the United States, millions of miles of pipeline carrying everything from water to crude oil. The pipe is vulnerable to attack by internal and external corrosion, cracking, third party damage and manufacturing flaws. If a pipeline carrying water springs a leak bursts, it can be a problem but it usually doesn't harm the environment. However, if a petroleum or chemical pipeline leaks, it can be a environmental disaster. In an attempt to keep pipelines operating safely, periodic inspections are performed to find flaws and damage before they become cause for concern.

When a pipeline is built, inspection personnel may use visual, X-ray, magnetic particle, ultrasonic and other inspection methods to evaluate the welds and ensure that they are of high quality. The image to the left show two NDT technicians setting up equipment to perform an X-ray inspection of a pipe weld. These inspections are performed as the pipeline is being constructed so gaining access the inspection area is not problem. In some areas like Alaska, sections of pipeline are left above ground like shown above, but in most areas they get buried. Once the pipe is buried, it is undesirable to dig it up for any reason.

Have you ever felt the ground move under your feet? If you're standing in New York City, it may be the subway train passing by. However, if you're standing in the middle of a field in Kansas it may be a pig passing under your feet. Huh??? Engineers have developed devices, called pigs, that are sent through the buried pipe to perform inspections and clean the pipe. If you're standing near a pipeline, vibrations can be felt as these pigs move through the pipeline. The pigs are about the same diameter of the pipe so they range in size from small to huge. The pigs are carried through the pipe by the flow of the liquid or gas and can travel and perform inspections over very large distances. They may be put into the pipe line on one end and taken out at the other. The pigs carry a small computer to collect, store and transmit the data for analysis. In 1997, a pig set a world record when it completed a continuous inspection of the Trans Alaska crude oil pipeline, covering a distance of 1,055 km in one run.

Pigs use several nondestructive testing methods to perform the inspections. Most pigs use a magnetic flux leakage method but some also use ultrasound to perform the inspections. The pig shown to the left and below uses magnetic flux leakage. A strong magnetic field is established in the pipe wall using either magnets or by injecting electrical current into the steel. Damaged areas of the pipe can not support as much magnetic flux as undamaged areas so magnetic flux leaks out of the pipe wall at the damaged areas. An array of sensor around the circumference of the pig detects the magnetic flux leakage and notes the area of damage. Pigs that use ultrasound, have an array of transducers that emits a high frequency sound pulse perpendicular to the pipe wall and receives echo signals from the inner surface and the outer surface of the pipe. The tool measures the time interval between the arrival of a reflected echos from inner surface and outer surface to calculate the wall thickness.

On some pipelines it is easier to use remote visual inspection equipment to assess the condition of the pipe. Robotic crawlers of all shapes and sizes have been developed to navigate the pipe. The video signal is typically fed to a truck where an operator reviews the images and controls the robot.

Solar-Powered Cars to Compete in Harrowing Race Across the Australian Outback

A four-passenger, solar-powered car named "Violet" is driving thousands of miles across Australia. But that trip is just the precursor to a harrowing race that spans the punishing landscape of the country's outback and is open only to vehicles powered by the sun.

The car, which was designed and built by engineering students from the University of New South Wales (UNSW), departed Sydney, Australia, on Sept. 20 and will travel about 2,700 miles (4,300 kilometers) to Darwin, on the continent's northern coast. This scenic route allows the team to test the car, and serves as a regional outreach tour, introducing their fellow highway drivers to the car's futuristic design.

Then, on Oct. 8, Violet will take part in the 30th Bridgestone World Solar Challenge, competing against 47 teams representing 21 nations. 

The race will take them from Darwin in the Northern Territories to Adelaide in South Australia, covering 1,877 miles (3,021 km). Though the event is scheduled to last from Oct. 8 to Oct. 15, the winner is expected to cross the finish line in Adelaide's Victoria Square in the early hours of Oct. 12, officials with the World Solar Challenge announced in a statement.

Violet is the sixth iteration of a solar-powered race car produced by UNSW's Sunswift team, which formed in 1995 to compete in the World Solar Challenge. Described by UNSW representatives as "a four-seater sedan" and larger than previous generations of Sunswift's solar race cars, Violet was deliberately crafted to resemble commercially produced vehicles, in order to showcase solar technology as a potential energy source for practical, daily use in transportation, Sunswift representatives explained on the group's website

.  

With a shell made of carbon fiber, the car weighs about 880 lbs. (400 kilograms) and it uses about 7 kilowatts of horsepower at 68 mph (110 km/h) — "as much power as a four-slice toaster," Sunswift team leader Simba Kuestler said in a statement

Source: www.livescience.com

Engineers are unveiling - the transistor laser that could be used to boost computer processor speeds.

Modern computers are limited by a delay formed as electrons travel through the tiny wires and switches on a computer chip. To overcome this electronic backlog, engineers would like to develop a computer that transmits information using light, in addition to electricity, because light travels faster than electricity.

Having two stable energy states, or bistability, within a transistor allows the device to form an optical-electric switch. That switch will work as the primary building block for development of optical logic -- the language needed for future optical computer processors to communicate, said Milton Feng the Nick Holonyak Jr. Emeritus Chair in electrical and computer engineering and the team lead in a recent study.

"Building a transistor with electrical and optical bistability into a computer chip will significantly increase processing speeds," Feng said, "because the devices can communicate without the interference that occurs when limited to electron-only transistors."

In the latest study, the researchers describe how optical and electrical bistable outputs are constructed from a single transistor. The addition of an optical element creates a feedback loop using a process called electron tunneling that controls the transmission of light. The team published its results in the Journal of Applied Physics.

Feng said the obvious solution to solving the bottleneck formed by big data transfer -- eliminating the electronic data transmission of the transistor and use all optics -- is unlikely to happen.

"You cannot remove electronics entirely because you need to plug into a current and convert that into light," Feng said. "That's the problem with the all-optical computer concept some people talk about. It just is not possible because there is no such thing as an all-optical system."

Feng and Holonyak, the Bardeen Emeritus Chair in electrical and computer engineering and physics, in 2004 discovered that light -- previously considered to be a byproduct of transistor electronics -- could be harnessed as an optical signal. This paved the way for the development of the transistor laser, which uses light and electrons to transmit a signal.

The new transistor could enable new devices and applications that have not been possible with traditional transistor technology.

"This is a single device that provides bistability for both electrical and optical functions with one switch," Feng said. "It is totally new, and we are working hard to find more new applications for the device."

Feng and his team have demonstrated electro-optical bistability at -50 degrees Celsius. The next step will be to prove that the device can work at room temperature. Feng said that they recently achieved this milestone, and the details will be published in an upcoming report.

"Any electronic device is virtually useless if it can't operate at room temperature," Feng said. "Nobody wants to carry a device in a refrigerator to keep it from getting too hot!"

---

Story Source:

Materials

provided by University of Illinois at Urbana-Champaign. Note: Content may be edited for style and length.

Argon Arc Welding

In any industry of the modern Steel-Age existence of welding technology is a must. And MMAW (Manual Metal Arc Welding), SM AW (Stick Metal Arc Welding), and GTAW (Gas Tungsten Arc Welding) are firmly established. This is because of their flexibility, utility in all positions and locations and easy availability of the consumables required for various types of welding’s.

In most of our industries the jobs for welding are being done using various types of stick or coated electrodes.

But the industrialists of the present day are increasing their productivity with a view to combating competition—both from internal and international markets—especially when the industry worldwide is becoming more and more competitive and industrial management is continuously seeking new ways and means to reduce cost and improve quality control.

Under the situation, users want to modernize their machines to run faster, longer and more efficiently. And they are seeking various advantages of Automatic and Semi-Automatic welding processes—MIG/MAG, TIG, GTAW or Gas-shielded Arc Welding—which are most modernized Machine Tools of Welding Technology. Argon Arc or Gas-shielded Arc welding is the most popular among them.

Now, let us consider inert gases and their utilisation in welding science. An inert gas is, as its name suggests, an inactive gas. It is used to protect the molten pool from the atmospheric air at the time of welding. Important inert gases are Helium and Argon. They are used with other Shielding-gases.

The Shielding gases may be classed into two groups

(1) Gases soluble in or reacting with metals. These are Hydrogen, Carbon dioxide, Nitrogen etc.

(2) Inert gas like Helium and Argon.

Argon and Carbon dioxide are the most widely used. Argon is obtained as a by-product in the separation of air to produce oxygen. Argon is supplied in steel-drawn cylinders under a pressure of 150 atmospheres. Purified argon contains 97-98 per cent argon, while commercial argon contains 13-14 per cent nitrogen.

It is convenient to consider that the application of gases which involve shielding the arc with argon, helium and carbon dioxide (CO2) and mixtures of argon with oxygen and CO2, helium are essential.

Argon is used as a shielding gas because it is chemically inert and forms no compounds. Commercial grade purity of argon is about 99.996% and obtained by fractional distillation of liquid air from the atmosphere. It is cheaper and is therefore used for commercial purposes.

Argon in commercial purity state is used for metal welding purpose. Argon with 5% hydrogen gives increased welding speed and penetration in the welding of stainless steel and Nickel alloys.

Helium may be used for aluminium and its alloys and copper. But Helium is more expensive than Argon and, due to its lower density, a greater volume is required than Argon to ensure shielding. A small variation in arc length causes greater changes in weld conditions.

The mixture of 30% Helium and 70% Argon gives fast welding speeds. The mechanised D.C. welding of aluminium with Helium gives deep penetration and high speeds.

Automatic Argon-arc welding has been successfully employed for welding thin stainless steel, aluminium and its alloys. The Argon-Arc Process may use either non-consumable or consumable electrodes. With a non-consumable electrode, the arc is maintained between a tungsten electrode and the ‘Work’. A shield of Argon is projected around the electrode.

The arc burns between a tungsten electrode and the work-piece within a shield of the inert gas argon, which excludes the atmosphere and prevents contamination of electrode and molten metal. The hot tungsten arc ionizes argon atoms within the shield to form a gas plasma consisting of almost equal numbers of free electrons.

Unlike the electrode in the manual metal arc process, the tungsten is not transferred to the ‘Work’.

The heat source in the inert gas arc welding process is an electric arc between a tungsten electrode and the parent metal. The electrode is shielded by a stream of inert gas—argon or helium—which eliminates the necessity of adding flux.A.C. is generally used with tungsten electrodes, and D.C. with the consumable metal arc electrode. This process is used for welding light alloys, some non-ferrous metals—especially aluminium, copper and their alloys, and also stainless steel.

With a consumable electrode, the arc is maintained between a metal electrode and the ‘Work’. Steel is widely welded by the Semi-automatic C02 shielded arc process. In aircraft industry Argon arc welding is used in a large scale even though it is a costly welding. Before its use the argon should be dried by passing through caustic or silica-gel

It has been successfully employed for welding thin stainless steel, aluminium and its alloys, copper and its alloys, nickel and its alloys, titanium, zirconium, silver, etc. The gas-shielded tungsten arc process enables these metals and a wide range of ferrous alloys to be welded without the use of the flux. This is a great advantage in all such welding’s.

Saudi Arabia just announced plans to build a $500 billion mega-city that's 33 times the size of New York City

• The Saudi Arabian government says it will build a $500 billion mega-city, with the goal of diversifying its economy to focus less on crude oil.
• The project, called NEOM, will measure 10,230 square miles.
• Saudi Crown Prince Mohammed bin Salman said the government will aim to make NEOM run on 100% renewable energy - a highly ambitious goal.

---

A screenshot from the "Discover NEOM" website

Saudi Arabia is the world's largest oil exporter , but falling oil prices have made it more difficult for the country to pay its oil workers.

Now the Saudi Arabian government has come up with a project that could give its economy a boost: a $500 billion mega-city that will connect to Jordan and Egypt and be powered completely by renewable energy.

On Tuesday, Saudi Crown Prince Mohammed bin Salman announced the project , called NEOM , at the Future Investment Initiative conference in Riyadh. It will be financed by the Saudi government and private investors, according to Reuters.

The business and industrial-focused city will span 10,230 square miles . To put that size in perspective, 10,230 square miles is more than 33 times the land area of New York City.

NEOM's larger goal is to lessen Saudi Arabia's reliance on oil exports, which could expand the country's economy beyond oil, bin Salmon said at the conference. The city will focus on a variety of industries, including energy and water, biotechnology, food, advanced manufacturing, and entertainment. Saudi Arabia hasn't released a masterplan yet for what it will look like.

The country appointed Klaus Kleinfeld, a former chief executive of Siemens AG and Alcoa Inc, to run the NEOM project. Officials hope that a funding program, which includes selling 5% of oil giant Saudi Aramco, will raise $300 billion for NEOM's construction.

The project could make NEOM one of the largest cities to run without fossil fuels. In the US, one of the largest cities to run on 100% renewable energy is Burlington, Vermont , which doesn't come close to the planned size of NEOM. Cities in Iceland and Norway also claim to be close to achieving entirely renewable electrical grids with help from natural resources like hydropower and geothermal heat.

Saudi Arabia expects to complete NEOM's first section by 2025.

"This place is not for conventional people or conventional companies, this will be a place for the dreamers for the world," bin Salmon said on a panel at the conference. "The strong political will and the desire of a nation. All the success factors are there to create something big in Saudi Arabia."

Saudi Crown Prince Mohammed bin Salman, Masayoshi Son, SoftBank Group Corp. Chairman and CEO, and Christine Lagarde, International Monetary Fund (IMF) Managing Director, attend the Future Investment Initiative conference in Riyadh, Saudi Arabia October 24, 2017

Octopus-Inspired Robots: Silicone Skin Can Change Texture for '3D Camouflage'

In a flash, an octopus can make like ragged-edged seaweed or coral by changing the color and texture of its skin, thus becoming nearly invisible in its environment. And in the future, robots may be able to pull off this seemingly magical camouflage trick as well.

Researchers have created a synthetic form of cephalopod skin that can transform from a flat, 2D surface to a three-dimensional one with bumps and pits, they report today (Oct. 12) in the journal Science. This technology could one day be used in soft robots, which are typically covered in a stretchy silicone "skin," the researchers said.

"Camouflaged robots may hide and be protected from animal attacks and may better approach animals for studying them in their natural habitats," Cecilia Laschi, a professor of biorobotics at the BioRobotics Institute of the Sant'Anna School of Advanced Studies, in Pisa, Italy, wrote in an accompanying article in the current issue of Science. "Of course, camouflage may also support military applications, where reducing a robot's visibility provides it with advantages in accessing dangerous areas," wrote Laschi, who wasn't involved in the current study. 

Bumpy skin

The researchers, led by James Pikul of the University of Pennsylvania and Robert Shepherd of Cornell University, took inspiration from the 3D bumps, or papillae, that octopus and cuttlefish can inflate using muscle units in one-fifth of a second for camouflaging. [8 Crazy Facts About Octopuses]

The complement of papillae in a soft robot would be the air pockets, or "balloons," beneath the silicone skin. Often, these pockets get inflated at different times in different spots to generate locomotion in a robot. In the new research, this robotic inflation was taken a step further.

"Based on these things they [cephalopods] can do and what our technology can't do, how do we bridge the gap to have technological solutions to their pretty amazing capabilities?" was the central question posed by Shepherd.

"In this case, inflating a balloon is a pretty feasible solution," he added.

By embedding small fiber-mesh spheres into the silicone, the scientists could control and shape the texture of the inflated surface, just as an octopus might retexture its skin.

Pikul, then a postdoctoral student at Cornell University, came up with the idea of texturing these air pockets via patterns of the fiber-mesh rings. He was drawn to the idea of inflating silicone because of how quick and reversible the inflation could be, Pikul explained to Live Science. From there, it was just a matter of figuring out the mathematical models to make it work.

Proof of concept

The current prototype for the textured skins looks fairly rudimentary: By dividing up the silicone bubbles with concentric circles of fiber-mesh frames, the researchers figured out how to control the shape of the silicone as it inflated. They managed to inflate the bubbles into some new shapes by reinforcing the mesh, according to the paper. For instance, they created structures that mimicked rounded stones in a river as well as a succulent plant (Graptoveria amethorum) with leaves arranged in a spiral pattern.

But sophistication wasn't their primary goal, Shepherd noted.

"We don't want this to be a technology that only a few people in the world can use; we want it to be fairly easy to do," Shepherd told Live Science. He wanted the texturing technology, which built on the team's earlier findings on how to make color-changing silicone skins, to be accessible to industry, academia and hobbyists alike. Therefore, the team deliberately used limiting technologies like laser cutters to manufacture the wire rings because that's what people outside a Cornell University lab could use.

Itai Cohen, a physics professor at Cornell, who also worked on the research, noted another accessible aspect of the technology. On an excursion into the field, Cohen envisions stacking sheets of deflated silicone — programmed to inflate into a camouflaging texture — into the back of one's truck. "Now, you can inflate it so it doesn't have to be in that permanent shape, which is really difficult to transport," Cohen told Live Science. As the technology advances, one might even be able to scan an environment and then program the corresponding silicone sheet right then and there to mimic it, Cohen speculated.

Both Pikul and Shepherd plan to pursue this technology in their own respective labs. Shepherd explained that since developing the technology, he's started to replace the inflation with electric currents that could cause the same texturing — no tether and pressurized air system required. And Pikul hopes to apply the lessons learned from manipulating the surfaces of materials to things where surface area plays a significant role, like batteries or coolants, he said.

"We're still very much in the exploratory phase of soft robotics," Shepherd said. Because most machines are made up of hard metals and plastics, the conventions and best uses of soft robots have yet to be fully fleshed out. "We're just at the beginning, and we have great results," he said, but the key is, "in the future, making it easier for other people to use the technology and making sure these systems are reliable."

The study was funded by the U.S. Army Research Laboratory's Army Research Office.

A transparent flexible screen is the latest invention that will help create bendable phones.

A flexible screen allows a mobile phone to bend and stretch, making it more durable. Flexibility also allows for new input methods. For example, you could flex the phone backwards or forwards to zoom in or out, to enlarge or reduce text size, and so forth.But perhaps the biggest advantage with this technology is it gives you a greater screen to phone size ratio.

A limitation with current mobile phones is that if you want a bigger screen display, you need to have a bgger phone. The bigger the phone - the less convenient it is to carry.

But with flexible screen technology, mobile phones with large screen displays can be bent, folded or rolled-up into a compact size to fit any pocket.

The idea of bendable phones has been around for awhile but the touch screens in use couldn't tell the difference between the touch of a finger, a stretch, or a bend.

However, a recent breakthrough by scientists at the University of British Columbia (UBC) in Vancouver, Canada may have solved this problem.

John Madden, a research scientist at the Massachusetts Institute of Technology (MIT) before joining UBC, has developed with his team of engineers a new transparent touch-sensitive flexible screen. The screen is made from a type of hydrogel - a material similar to that used to make soft contact lenses.

What is unique about this latest invention is that electrically charged molecules flowing through the hydrogel projects an electric field beyond the flexible screen. When finger(s) approach the display, it can detect and distinguish them from a stretch or bend in the screen.The hydrogel flexible screen is then connected to an electronic operating system and embedded into thin silicone rubber to create a bendable phone or tablet.

According to Madden, their hydrogel flexible screen is not soft or weak like how most people think of gels, but very tough (it's been used to replace cartilage), can stretch 20 times its size and is inexpensive to manufacture.

Sources: ece.ubc.ca; advances.sciencemag.org;samsung.com; dailymail.co.uk

                                 Plastic Welding

Plastic welding is the process of creating a molecular bond between two compatible thermoplastics. Welding offers superior strength, and often drastically reduced cycle times, to mechanical joining (snap fits, screws) and chemical bonding (adhesives). There are three main steps to any weld: pressing, heating, and cooling. The application of pressure, which is often used throughout both the heating and cooling stages, is used to keep the parts in the proper orientation and to improve melt flow across the interface. The purpose of the heating stage is to allow intermolecular diffusion from one part to the other across the faying surface (melt mixing). Cooling is necessary to solidify the newly formed bond; the execution of this stage can have a significant effect on weld strength.

There are several possible methods of plastic welding: Ultrasonics, Vibration, Spin, Hot Plate, Laser / Infrared, Radio Frequency, and Implant are the most common. These plastic welding processes are primarily differentiated by their heating methods. The application of pressure and allowances for cooling are mechanical considerations may vary from machine to machine within the general process category.

Pressure

The use of pressure during the weld serves multiple purposes:

• Flattens surface asperities to increase part contact at joint
• Maintains orientation of part
• Compresses melt layer to encourage intermolecular diffusion between the two parts
• Prevents formation of voids from part shrinkage during cooling

Historically, pressure has been applied for plastic welding through the use of pneumatic presses. Recently, however, servo motors have been employed for at least a few of the common processes. Pneumatic welders are economical and well-suited to most simple applications. The precision of servo motion, however, offers greater control and precision which is desirable for more difficult applications or when the equipment is used for a wide variety of applications.

Heating

It is crucial to the plastic welding process to form a melt layer at the faying surface to allow intermolecular diffusion for formation of a molecular bond. In the solid state, polymer chains will not flow. Therefore, the joint surface on both of the parts must be melted to allow the plastic molecules to diffuse across the interface and bond with molecules of the other part. The hotter the melt is, the more molecular movement is achieved, and a weld can be made in a shorter cycle time. Amorphous polymers must be heated to above their glass transition temperature while semi-crystalline polymers must be heated to above their melting temperature.
In all types of plastic welding, only a thin layer of the parts are melted near the joint. It would be impractical to heat the entire part for several reasons:

• Heating only a small area takes less time, and reduces cooling time
• Limiting the melt also reduces the heat affected zone
• Maintains the molded micro structure of the bulk of the part
• Prevents excess shrinkage or warpage during cooling
• Allows rigid support of the part during welding

Ultrasonic plastic Welding

Ultrasonic plastic welding is the joining or reforming of thermoplastics through the use of heat generated from high-frequency mechanical motion. It is accomplished by converting high-frequency electrical energy into high-frequency mechanical motion. That mechanical motion, along with applied force, creates frictional heat at the plastic components' mating surfaces (joint area) so the plastic material will melt and form a molecular bond between the parts.  The following drawings illustrate the basic principle of ultrasonic welding.

NDT FOR WIND TURBINES

NDT techniques for wind turbines

Because mass production of wind turbines is fairly new, no manufacturing standards have been set yet. Efforts are now being made in this area on the part of both the government and manufacturers.

While wind turbines on duty are relied on to work 90 percent of the time, many structural flaws are still encountered, particularly with the blades. Cracks sometimes appear soon after manufacture. Mechanical failure, due to alignment and assembly errors, is common. Electrical sensors frequently fail because of power surges. Non-hydraulic brakes tend to be reliable, but hydraulic braking systems often cause problems

Manufacturing flaws on turbine blades

Manufacturing flaws can cause problems during normal operation. For example, blades can develop cracks at the edges, near the hub or at the tips . Fiberglass rotor blades are regarded as the most vulnerable components of a wind turbine.

Typical manufacturing flaws on the blades may be summarized as delaminations , adhesive flaws and resin-poor areas. Here are some specific flaws at particular locations:

•     Skin/adhesive: this is bad cohesion between the skin laminate and the epoxy or the epoxy is missing.
•     Adhesive/main spar: this is when there is no cohesion between the adhesive and the main spar.
•    De lamination in main spar laminate.

•    High damping in skin or main spar laminate, which could be caused by porosities or change of thickness of laminate.

Manufacturing flaws on the tower

A tubular tower is made of a lot of sheets of iron that are welded together. A flange is welded onto each end of the sections. The welding is checked thoroughly using ultrasonic NDT.

 NDT techniques at manufacture

Visual inspection

Relatively advanced NDT testing methods are used to examine rotor blades. The methods employed include penetrant testing and visual inspection with the use of miniature cameras or endoscopes.

At present, it appears that mechanical components aren’t tested at manufacture but the cause of their damage can be determined. For example, endoscopes are used for the visual inspection of planetary gear transmissions. However, damaged components are usually examined in a materials laboratory.

Ultrasonic NDT

An ultrasonic test can be carried out to investigate if any damage is present in the wind turbine blade. Ultrasonic inspection reveals these flaws quickly, reliably and effectively and is the most often used non-destructive composite inspection method in industry. The main advantage of ultrasound scanning is that it enables us to see

beneath the surface and check the laminate for dry glass fibre and delamination.

Tap test

The tap test can be used to verify some of the results from the ultrasonic test and it is also a good method to discover irregularities in the structure. The method is based on the fact that the sound emitted when knocking on the structure changes when the thickness or material type changes or when porosities are present. It could also be caused when there is a dis bond between the skin laminate and the main spar. There are three types of tap testing equipment; a manual tapping hammer, the ‘Woodpecker’ portable bond tester and the Computer Aided Tap Tester (CATT) system.

All the automated tap methods have the advantage that they can produce a print of the damaged area, which is both useful and a permanent record of the damage found. All the tapping methods work well for thin laminates, honeycomb structures and other sandwich panels but are not so effective on thicker parts.

 Infrared thermography

The adhesive joints are critical points in the blade structure. That is why they are inspected with particular care. Infrared (IR) scanners are used to examine the blade throughout its length, measuring exactly the same points each time. The scanner is able to see through the laminate and check the adhesive joint. It records temperature differences in the adhesive, possibly identifying flaws, and takes a series of pictures. If there are any doubts, a point can be highlighted

and later analyzed using electronic image processing. If flaws are found, they can almost always be repaired immediately.

Flaws and NDT in-service

As the force of the wind is so irregular, the driving mechanism of a wind turbine is subject to much greater dynamic loads. Virtually all components of a wind turbine are subject to damage, including everything from the rotor blades to the generator, transformer, nacelle, tower and foundation.Wind turbines do have regular maintenance schedules in order to minimize failure. They undergo inspection every three months, and every six months a major maintenance check-up is scheduled. This usually involves lubricating the moving parts and checking the oil level in the gearbox. It is also possible for a worker to test the electrical system on site and note any problems with the generator or hook-ups

Flaws on turbine blades

In-service flaws have been identified in the following report: Risø-R-1391(EN) ‘Identification of Damage Types in Wind Turbine Blades Tested to Failure’ Christian P. Debel, AFM. ISBN 87-550-3178-1; ISBN 87-550-3180-3  ISSN 0106-2840

Flaws on rotor bearings

Cyclic stresses fatigue the blade, axle and bearing material, and were a major cause of turbine failure for many years. When the turbine turns to face the wind, the rotating blades act like a gyroscope. As it pivots, gyroscopic precession tries to twist the turbine into a forward or backward somersault. For each blade on a wind generator’s turbine, precessive force is at a minimum when the blade is horizontal and at a maximum when the blade is vertical. This cyclic twisting can quickly fatigue and crack the blade roots, hub and axle of the turbine.

Spalling (breaking up into fragments) of rotor shaft bearings can result in cracked rings, and in some cases, revolution of the inner rings around the shaft causes cracks in the shaft that can result in a total loss of the turbine. illustrates what can happen when the rotor bearings fail (in this case the blades landed 1 km away after having crossed a road)

TESTING PROCEDURE

Acoustic emission

A substantial amount of work has gone on in AE since 1993. A fatigue test of a wind turbine blade which was conducted at the National Renewable Energy Laboratory shows that fatigue tests of large FRP wind turbine blades can be monitored by AE techniques and that the monitoring can produce useful information. AE testing procedures, developed during a laboratory blade testing programme, have been applied to an in-service wind turbine blade in 2003. In the Framework of the Non-Nuclear Energy Programme, JOULE III from 1998 to 2002, the partners successfully developed a methodology for the structural integrity assessment of wind turbine blades, either in-service, or during certification testing, based on Acoustic Emission monitoring during static or fatigue loading. Within the framework of JOULE III, specialized pattern recognition software for AE data analysis and wind turbine automatic structural integrity assessment has been developed

Full scale testing of wind turbine blade to failure

A 25 m wind turbine blade was tested to failure when subjected to a flap wise load. With the test setup, it was possible to test the blade to failure at three different locations. The objective of these tests is to learn about how a wind turbine blade fails when exposed to a large flap wise load and how failures propagate. The report also shows results from the ultrasonic scanning of the surface of the blade and it is seen to be very useful for the detection of flaws, especially in the layer between the skin laminate and the load carrying main spar. AE was successfully used as sensor for the detection of damages in the blade during the test.

Wireless detection of internal delamination cracks in CFRP

In this study, a wireless system using a tiny oscillation circuit for detecting delamination of carbon/epoxy composites is proposed. A tiny oscillation circuit is attached to the composite component. When delamination of the component occurs, electrical resistance changes, which causes a change in the oscillating frequency of the circuit. Since this system uses the composite structure itself as a sensor and the oscillating circuit is very small, it is applicable to rotating components. The wireless method is found to successfully detect embedded delamination, and to estimate the size of the delamination.

Structural health monitoring techniques for wind turbine blades

These experiments indicate the feasibility of using piezoceramic

patches for excitation and a Scanning Laser Doppler Vibrometer or piezoceramic patches to measure vibration to detect damage.

Further testing of different smaller damages and types of damage is needed to verify the sensitivity of the methods. The resonant comparison method can be used for operational damage detection while the operational deflection shape method produces non-symmetric contours that are an easily interpretable way to detect damage in a structure that is not moving.

Infrared thermography for condition monitoring of composite wind turbine blades

Infrared thermography has the potential for providing full-field non-contacting techniques for the inspection of wind turbine blades(10). For application to turbine blades, the sensitivity of the thermal imaging has been shown to be suitable for non-destructive examination during fatigue testing; furthermore, it is thought that for blades in situ, the wind loading conditions may be sufficient to create effects detectable by thermal imaging.