Long Range Ultrasonic Inspection (Guided Wave UT

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LONG RANGE ULTRASONIC INSPECTION (GUIDED WAVE UT) : 

LONG RANGE ULTRASONIC INSPECTION (GUIDED WAVE UT) Mostafa Mahmoud

WHAT IS LRUT? : 

The Long Range Guided Wave Ultrasonic Technique (LRGUT) is designed to inspect 100 percent of a pipe segment from one single location.Torsional or longitudinal guided waves are induced into the pipe body and propagated along the pipe segment being inspected. When these guided waves identify an anomaly or pipe feature, they mode convert into laminar waves and reflect back to the tools original location. Using a laptop these signals are digitally captured. The time-of-flight for each signature is calculated to determine it's distance from the tool. The cross sectional area is calculated by amplitude and then the circumferential extent determined by the focused beams (broken down in octants) to determine the significance of the defect. WHAT IS LRUT? By : Mostafa Mahmoud

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By : Mostafa Mahmoud

WHAT IS LRUT? : 

WHAT IS LRUT? Long range (or guided wave) ultrasonic inspection is different from conventional ultrasonic inspection, since a ring of transducers fitted round the outside of the part being inspected sends a sound wave along the length of the component, rather than through it. The component itself (more often than not, a pipe) constrains, or guides, the waves along the pipe wall, hence the term 'guided waves'. By : Mostafa Mahmoud

WHAT IS LRUT? : 

Guided waves are a special case of plate waves in a pipe. The particle displacements are similar, but because the pipe acts as a wave-guide, the pulses can travel over even longer distances, exceeding 100m under some conditions. Figure 1 illustrates the principal wave modes that can be generated in pipe. WHAT IS LRUT? By : Mostafa Mahmoud

WHAT IS LRUT? : 

The variation of velocity with frequency, wave mode, pipe diameter and wall thickness is illustrated by means of dispersion curves. A simplified illustration showing four wave modes only is shown in Figure. These are for a specific pipe diameter and wall thickness. Other diameters and thicknesses will have their own families of dispersion curves. WHAT IS LRUT? By : Mostafa Mahmoud

WHAT IS LRUT? : 

It can be seen that the Torsional T(0,1) wave is non-dispersive. Its velocity is constant irrespective of frequency. The Longitudinal L(0,1) wave is highly dispersive with wide variations in velocity with frequency. The Longitudinal L(0,2) wave cannot exist at frequencies below about 20 kHz. However, at frequencies above about 40 kHz, the velocity becomes nearly constant with changing frequency. That is the wave becomes non-dispersive. WHAT IS LRUT? By : Mostafa Mahmoud

WHAT IS LRUT? : 

There is a vast range of flexural waves. Only the dispersion curve for the Flexural F(1,3) mode is shown. This wave can only exist at frequencies above ~25 kHz. Like the L(0,2) wave it becomes almost non-dispersive at frequencies above about 50 kHz. Dispersive waves are undesirable because the pulse widens as it travels along the pipe and variation in the velocity of the wave makes it difficult to determine the exact position of any reflector along the pipe. Because their velocity is influenced by wall thickness, guided waves exhibit their most important characteristic for NDT; that of being sensitive to changes in wall thickness. They are therefore sensitive to corrosion or erosion, whether it is on the inside surface or the outside surface of the pipe. They are also sensitive to cracks provided that they present a significant planar reflection transverse to the axis of the pipe. WHAT IS LRUT? By : Mostafa Mahmoud

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By : Mostafa Mahmoud

LRUT PREPARATION : 

LRUT PREPARATION Access to pipe surface, approximately 1 meter length required at each test point. Coating needs to be removed for approximately 1 meter at the collar locations. The surface in this area should be free from loose scale, rust etc. Clearance around pipe 10 to 20 cm. By : Mostafa Mahmoud

LRUT APPLICATIONS : 

LRUT APPLICATIONS Insulated Pipe in Refineries• Offshore Pipeline Risers• Cased Road or Railway Crossings• Loading Lines and associated Pipe work• Tank Dyke Pipeline Crossings• Above Ground or Buried Flow Lines• River or Bridge Pipeline Crossings• As part of ECDA & ICDA Methodologies By : Mostafa Mahmoud

LRUT CAPABILITIES : 

LRUT CAPABILITIES Set up time is approximately 15 - 20 minutes. Inspection of as much as 1km of pipe per day under good conditions. Provides 100% coverage on straight sections. Bends may need separate scans. Suitable for pipe diameters 2" to 60". Equally applicable to carbon and stainless steel. Sensitive to both internal and external metal loss (corrosion under insulation). Detects wall losses in excess of 9% pipe wall cross section. Discriminates between defects and features such as welds, bends and pipe supports. May be used on piping in oil, gas and petrochemical installations (< 125oC). Can scan inaccessible regions including sleeved pipes, under pipe supports, storage tank bund wall penetrations, road crossings, under bridges, jettys, offshore risers etc. By : Mostafa Mahmoud

LRUT LIMITATIONS : 

LRUT LIMITATIONS May not be applicable to some coated pipes (concrete, bitumastic or Denzo™). Less effective on lines having a large number of bends or branches or on very convoluted pipe. May not be applicable to lines containing sludgy liquids. These and waxy deposits can reduce test range. May not be applicable for detection of small isolated corrosion pits. By : Mostafa Mahmoud

LRUT BENEFITS : 

LRUT BENEFITS The technology can inspect up to 150m of pipe from a single location and provides 100% direct assessment of pipe lengths. The benefits of LRUT include: Rapid screening for in-service degradation Cost reduction in gaining access to the pipes for inspection. Avoidance of removal and reinstatement of insulation or coatings (where present), except for the area on which the transducer tool mounted. The ability to inspect inaccessible areas, such as at clamps or sleeved or buried pipes. The whole pipe wall is tested, thereby achieving a 100% examination. By : Mostafa Mahmoud

LRUT (T – SCAN) : 

LRUT (T – SCAN) The T-SCAN tube screening system is the latest development of Guided wave technology to non-destructively screen tubes, such as those found in heat-exchangers, air coolers and boilers, for defects. Note that T-scan is only a Commercial Name not a scientific name By : Mostafa Mahmoud

THE IDEA : 

THE IDEA The main idea behind this development is to enable a large number of tubes to be screened for defects in a fast and efficient way. This is achieved thanks to the following advantages of this system over current techniques: Reduction or even elimination of the need for extensive cleaning of tubes as is required for other techniques such as IRIS, MFL or EC. No probe pusher-puller units required. The probe is inserted from one end of the tube and stays in this position for the duration of the test. Quick set-up times, no calibration required. Once the defective tubes, which may only constitute a small percentage of the total number of tubes being inspected, have been identified they may be cleaned and precise sizing methods may be applied in a focused and cost-effective manner. By : Mostafa Mahmoud

THE TECHNOLOGY : 

THE TECHNOLOGY Ultrasonic guided waves are excited using an internal transducer probe at a single position near one end. These propagate in both directions along the entire length L of the tube. T-SCAN then detects reflections from defective areas Since guided waves occupy the entire cross-section of the tube, 100% of the tube is inspected. The probe head consists of an array of transducers which are dry-coupled to the inside wall of the tube through a pneumatic system, and is compatible with the Wave maker G3 Pipe Screening Instrument. By : Mostafa Mahmoud

FURTHER ADVANTAGES : 

FURTHER ADVANTAGES Apart from immense cost-savings through the elimination of the need for cleaning, there are further advantages: Can be used with any material (ferrous and non-ferrous). Very tolerant of tube geometry for example in the testing of twisted tubing, integral fin tubing etc. Ability to inspect U-bend area. By : Mostafa Mahmoud

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