Advanced NDT

In its simplest form, one can think of a phased array probe as a series of individual elements in one package. While the elements in reality are much smaller than conventional transducers, these elements can be pulsed as a group so as to generate directionally controllable wave fronts. This "Electronic Beam Forming" allows multiple inspection zones to be programmed and analyzed at very high rates of speed from a single position transducer.

The main advantages of phased array in NDE are:

TOFD Technique is based on the Diffraction of the ultrasonic wave on tips of discontinuities instead of geometrical reflections on the interface of the discontinuities. When Ultrasound is incident at linear discontinuity such as crack, diffraction takes place at its extremities. Usually it uses highly damped, short pulse Compression probes are attached in an array at a fixed distance.

The main advantages of TOFD in NDE are:

Guided waves are mechanical stress waves that propagate contained within the structural boundaries of pipes or plates with wavelengths that are comparable to the thickness dimensions of the pipe or plate. Guided waves are qualitative inspection technique used in rapid testing or screening tools to detect, locate and classify corrosion defects. Large sections of piping can be quickly screened with 100 percent volumetric coverage to determine precise locations of corrosion damage.

GWT sensor that is permanently mounted to the pipe. It offers an excellent solution to recurrent inspections where access to the test point is only required once. Further access cost for inspections is considerably reduced or completely eliminated. With the help of the data comparison module in the WavePro™ software, the monitoring data enables accurate tracking and trending of defects.

MFL technology is similar to Magnetic Particle Inspection (MPI) in which the component is magnetized to a level at which the presence of a significant local reduction in material thickness causes sufficient distortion of the internal magnetic field to allow flux lines to break the test surface at the site of the discontinuity. The distorted magnetic fields are received by the suitable sensors and are used to give an electrical sign. These signals are used by software and mapped for further interpretation and evaluation. This technique is used for the detection of pitting and corrosion in bottom plates of storage tanks.

In oil and petrochemical industry, variety of heat exchangers are used. The purpose of heat exchanger is to transfer heat between two or more fluids. Heat exchangers are used in both cooling and heating processes. Based on the application, there shape and dimension and material are different from each other. For a reliable and cost-effective operation, proper working of this equipment’s are necessary.

Frequent inspection is required to verify the integrity of the tubes from in-service deterioration like corrosion, erosion or cracks etc. Tube inspection techniques like Eddy current Testing, Remote Field Eddy Current Testing, Magnetic Flux Leakage Testing, Internal Rotary Inspection System are few among the commonly used methods for evaluating the condition of tubes.

The basic bobbin probe is made with two coils excited with an alternative current. This current creates a magnetic field that penetrates the tube material. In reaction to this magnetic field, opposite currents are induced in the tube material. Those currents are called “Eddy Current”. Any defects that change the eddy current flow circulation will change the impedance of the coils in the probe. Those changes in the impedance of the coils are measured and used to detect and size the defects in the tube.

The ET technique is the best method for inspection of non-ferrous tubing. The technique is suitable for austenitic stainless steel such as SS304/SS316, brass (70/30), copper-nickel, Inconel, titanium, copper-finned, and others.

The basic probe is made with one exciter and two receiver coils. Two primary paths exist for coupling the energy between the exciter and the receivers. The direct field is localized around the exciter and rapidly attenuate with distance down the pipe. The indirect field diffuses outward through the tube wall, moves along the tube, and re-diffuses back through the tube wall. The zone in which this indirect field is dominant is called the remote field zone. This append at a distance higher than two tubes diameters.

The basic probe is made with one exciter and two receiver coils. Two primary paths exist for coupling the energy between the exciter and the receivers. The direct field is localized around the exciter and rapidly attenuate with distance down the pipe. The indirect field diffuses outward through the tube wall, moves along the tube, and re-diffuses back through the tube wall. The zone in which this indirect field is dominant is called the remote field zone. This append at a distance higher than two tubes diameters.

with strong permanent magnets, coupled with a steel core, generate a strong magnetic field that saturates the tube wall. An absolute coil is winded around the core to measure magnetic field variation caused by general wall losses. When a small flaw is located between the two magnets, the magnetic field in the tube wall is disturbed and a small amount of flux leak into the inner side of the tube. This flux leakage is detected by a differential coil (Lead), located between the magnets. A trailing coil (Trail) at the end of the probe detects the residual magnetism coming from internal pits.

with strong permanent magnets, coupled with a steel core, generate a strong magnetic field that saturates the tube wall. An absolute coil is winded around the core to measure magnetic field variation caused by general wall losses. When a small flaw is located between the two magnets, the magnetic field in the tube wall is disturbed and a small amount of flux leak into the inner side of the tube. This flux leakage is detected by a differential coil (Lead), located between the magnets. A trailing coil (Trail) at the end of the probe detects the residual magnetism coming from internal pits.

In the IRIS technique, a transducer located inside a turbine generates an ultrasound pulse along the axis of the tube. The ultrasound is reflected on a 45° mirror and oriented toward the tube wall. When it reaches the internal surface of the tube, the ultrasound is partially reflected, then transmitted inside the tube wall, and finally reflected on the outside surface. The wall thickness of the tube can be calculated by using the ultrasound velocity in the tube material and the time of flight difference between the outside and inside diameter echoes.

Since IRIS is an ultrasonic technique, water is used as couplant. Tubes under test must therefore first be flooded to use this technique.

The IRIS technique can be used in any tube material (ferrous and nonferrous material) and for a wide range of tube diameter. The technique provides accurate wall thickness measurement and defect sizing.

It is an automated girth weld inspection system using phased array and conventional UT techniques (AUT). Specially designed for in-site weld-to-weld inspection in extreme environments, on-shore and off-shore.

Pipelines perform a critical function in the global economy, transporting huge volumes of gas, oil, water, and other chemicals. Pipes are girth-welded on-site, typically using automated welding systems. For construction of pipelines, welds are the "weak spot" as this is where defects tend to occur. Welds are nondestructively tested, coated, and buried or laid on the sea bed. Due to the demanding construction cycle, it is important that weld defects be detected and analyzed very quickly.

In the last several years, automated ultrasonic testing (AUT) has begun overtaking traditional radiography as the pipeline weld inspection method of choice throughout the world. Radiography has significant limitations: poor detection of planar defects, no vertical sizing capability, safety issues, and environmental concerns.

The advantages of AUT:

Computed Radiography is an alternative and advancement to conventional radiographic film, Computed radiography uses photostimulable phosphor image receptors.

When the radiation strikes on the phosphor plate, the radiation will stimulate the electrons to higher energy state. This entrapped electron in the higher energy state, will return to their respective bands by emitting radiation (light).

When this phosphor plate is exposed to small, high intensity laser beam. These lights will be collected and interpreted by photomultiplier tube to Analog signal and the same will be digitized using Analog to digital converter.

Once the image acquisition has been finished, the image plate can be reset and reused for another exposure. The advantage of the image plate over conventional radiography film are