ANGLE - BEAM CALIBRATION BLOCK IN ULTRASONIC INSPECTION.

The miniature angle-beam is a calibration Block that was designed for the US Air Force for use in the field for instrument calibration. The block is much smaller and lighter than IIW block but performs many of the same functions. The miniature angle-beam block can be used to check the beam angle and exit point of the transducer. The block can be used to make metal - distance and sensitivity calibrations for both angle and normal - beam inspection setups.

A block that closely resembles the miniature angle-beam block and is used in a similar way is the DSC AWS block. This block is used to determine the beam exit point and refracted angle of angle - beam transducers and to calibration distance and set sensitivity for both normal and angle beam inspection setups. Instructions on using the DSC block can be found in the annex of American society for testing and materials standard E164, standard practice for ultrasonic contact Examination of weldment.

The IIW Type Calibration Block in ultrasonic inspection.

The standard shown in the above figure is commonly known in the US as an IIW Type reference block. IIW is an acronym for the international Institute of welding. It is referred to as an IIW Type reference block because it was patterned after the true IIW block but does not conform to IIW requirements in IIS/IIW-23-59. True IIW blocks are only made out of steel (to be precise, killed, open hearth or electric furnace, low - carbon steel in the normalize condition with a grain size of McQuaid-ehn #8) where IIW Type blocks can be commercially obtained in a selection of materials. The dimensions of  true IIW blocks are in metric units while IIW  type blocks usually have English units. IIW type blocks may also include additional calibration and references features such as notches, circular groves, and scales that are not specified by IIW. There are two full -sized and a mini versions of the IIW Type blocks. The mini version is about one - half the size of the full-sized block and weighs only only about one-fourt as much. The IIW type US-1 block was derived the basic true IIW block and is shown below in the figure on the left. The IIW type US-2 block was developed for US air force application and is shown below in the center. The mini version is shown on the right.

IIW type blocks are used to calibrate instruments for both angle beam and normal incident inspections. Some of their uses include setting metal-distance and sensitivity settings,determining the sound exit point and refracted angle of angle beam transducers, and evaluating depth resolution of normal Beam inspection setups. 

Distance Amplitude correction (DAC) in ultrasonic inspection.

Acoustic signals from the same reflecting surface will have different amplitudes at different distances from the transducer. Distance Amplitude correction (DAC)  provides a means of establishing a graphic reference level sensitivity as a function of sweep distance on the A - scan display. The use of DAC allows signals reflected from similar discontinuities to be evaluated where signal attenuation as a function of depth has been correlated. Most often DAC will allow for loss in amplitude over material depth  (time), graphically on the A - scan display but can also be done electronically by certain instruments. Because near field length and beam spread vary according to transducer size and frequency, and materials vary in attenuation and velocity, a DAC cure must be established for each different situation. DAC may be employed in both longitudinal and shear modes of operation as well as either contact or immersion inspection techniques.
A distance Amplitude correction curve is constructed from the peak amplitude responses from reflectors of equal area at different distances in the same material. A-scan echoes are displayed at their non - electronically compensated height and peak amplitude of each signal is marked on the flaw detector screen or, preferably, on a transparent plastic sheet attached to the screen. Reference standards which incorporate side drilled holes (SDH), flat bottom holes (FBH),or notches whereby the reflectors are located at varying Depths are commonly used.

INTRODUCTION TO THE COMMON STANDARDS IN ULTRASONIC INSPECTION.

Calibration and reference standards for ultrasonic testing come in many shapes and sizes. The type of standard used is dependent on the NDE application and the form and shape of the object being evaluated. The material of the reference standard should be the same as the material being inspected and the artificially induced flaw should closely resemble that of the actual flaw. This second requirements is a major limitations of most standard reference samples. Most use drilled holes and notches that do not closely represent real flaws. In most cases the artificially induced defects in reference standards are better reflectors of sound energy (due to their flatter and smoother surfaces) and produce indications that are larger than those that a similar sized flaw would produce. Producing more realistic defects is cost prohibitive in most cases and, therefore, the inspector can only make an estimate of the flaw size. Computer programs that allows the inspector to creat computer simulated model of the part and flaw may one day lessen this limitation.

CALIBRATION METHODS IN ULTRASONIC INSPECTION.

Calibration refers to the act of evaluating and adjusting the precision and accuracy of measurement equipment. In ultrasonic testing, several forms of calibration must occur. First, the electronics of the equipment must be calibrated to ensure that they are performing as designed. This operation is usually performed by the equipment manufacturer and will not be discussed further in this material. It is also usually necessary for the operator to perform a user calibration of the equipment. This user calibration is necessary because most ultrasonic equipment can be reconfigure for use in a large variety of applications. The user must calibration the system which includes the equipment settings, the transducer, and the test setup, to validate that the desired level of precision and accuracy are achieved. The term calibration standard is usually  only used when an absolute value is measured and in many cases,the standards are traceable back to standards at the national institute for standards and technology.
In ultrasonic testing, there is also a need for reference standards. Reference standards are used to establish a general level of consistency in measurements and to help interpret and quantity the information contained in the received signal. Reference standards are used to validate that the equipment and the setup provide similar results from one day to the next and that similar results are produced by different systems. Reference standards also help the inspector to estimate the size of flaws. In a pulse-echo type setup, signal strength depends on both the size of the flaw and the distance between the flaw and the transducer. The inspector can use a reference standard with an artificially induced flaw of known size and at approximately the same distance away for the transducer to produce a signal.

Attenuation measurements in ultrasonic inspection.

Ultrasonic wave propagation is influenced by the microstructure of the material through which it propagates. The velocity of the ultrasonic waves is influenced by the elastic moduli and the density of the material, which in turn are mainly governed by the amount of various phases present and the damage in the material. Ultrasonic attenuation, which is the sum of the absorption and the scattering, is mainly dependent upon the damping capacity and scattering from the grain boundary in the material. However, to fully characterize the attenuation required knowledge of a large number of thermo-physical parameters that in practice are hard to quantity..

Relative measurements such as the change of attenuation and simple qualitative tests are easier to make than absolute measure. Relative attenuation measurements can be made by examining the exponential decay of multiple back surface reflections. However, significant variations in microstructure characteristics and mechanical properties often produce only a relatively small change in wave velocity and attenuation.
Absolute measurements of attenuation are very difficult to obtain because the echo amplitude depends on factors in addition to amplitude. The most common method used to get quantitative results is to use an ultrasonic source and detector transducer separated by a known distance. By varying the separation distance, the attenuation can be measured from the changes in the amplitude. To get accurate results, the influence of coupling conditions must be carefully addressed. To overcome the problems related to conventional ultrasonic attenuation measurements, ultrasonic spectral parameters for frequency - dependent attenuation measurements, which are independent from coupling conditions are also used. For example, the ratio of the amplitudes of higher frequency peak to the lower frequency peak, has been used for microstructure characterization of some materials. 

Time measurement technique in ultrasonic inspection.

Fourier Transform - phase - slope determination of delta time between received RF burst (T2-R)-(T1-R),where T2 and T1 EMATs are driven in series to eliminate differential phase shift due to probe liftoff.

Slope of the phase is determined by linear regression of weighted data points within the signal bandwidth and weighted y-intercept. The accuracy obtained with this method can exceed one part in one hundred thousand. 

The History of ship.

The history of shipbuilding and seafaring is a vast and fascinating subject that spans thousands of years. Here is a brief overview of the key milestones in the history of ships:

1). Early Watercraft:

* Rafts and canoes: The earliest forms of watercraft were simple rafts and canoes made from logs or reeds. These were used for fishing and transportation along rivers and lakes.

* Ancient Egypt: The Egyptians developed small sailboats called feluccas, which were used for trade along the Nile River and later the Mediterranean Sea.

2). Ancient Seafaring:

*Phoenician ships: The Phoenicians were renowned seafarers in the ancient world and developed advanced ships called galleys. These wooden vessels were propelled by oars and sails and were used for trade and exploration in the Mediterranean Sea.

* Greek triremes: The ancient Greeks developed triremes, which were highly maneuverable warships with three rows of oars on each side.

3) Age of Exploration:

* Viking longships: The Vikings were skilled shipbuilders and navigators, using their longships to explore and trade across the North Atlantic and European rivers.

*Age of Discovery: European nations, such as Spain, Portugal, and England, started building larger and more advanced ships to explore new trade routes and claim territories around the world. The caravel, a small, fast sailing ship, was widely used during this era.

*Age of Sail: The 16th to 19th centuries saw the golden age of sail, with ships like the galleon and frigate dominating the seas. These ships were equipped with multiple masts and square-rigged sails, enabling them to sail across oceans and engage in naval warfare.

4) Industrial Revolution and Steam:

*Industrial revolution: The invention of the steam engine in the 18th century revolutionized shipbuilding. Steam-powered ships, such as paddle steamers and later, screw-driven steamships, replaced sail as the primary means of propulsion.

*Iron and steel ships: The 19th century saw the transition from wooden ships to iron and steel construction. This allowed for larger, stronger, and more technologically advanced vessels, such as steam-powered ocean liners and ironclad warships.

5). Modern Shipping and Naval Technology:

*20th-century advancements: The 20th century witnessed further advancements in shipbuilding technology, including the use of diesel engines, improved navigation systems, and the introduction of specialized vessels such as submarines, aircraft carriers, and container ships.

*Modern shipbuilding: Today, shipbuilding is a highly specialized industry, utilizing advanced materials, computer-aided design, and sophisticated manufacturing techniques. Ships are designed to meet specific purposes, from cargo transportation and cruise liners to military vessels and research ships.

The history of ships reflects the evolution of human civilization, from early exploration and trade to colonization and the development of global maritime networks. Ships have played a crucial role in shaping our world by connecting cultures, facilitating trade, and enabling exploration and discovery.

Precision velocity measurements in ultrasonic inspection.

Electromagnetic - acoustic transducer (EMAT) generate ultrasound in the material being investigated. When a wire or coil is placed near to the surface of an electrically conducting object and is driven by a current at the desired ultrasonic frequency, eddy currents will be induced in a near surface region. If a static magnetic field is also present, these currents will experience Lorentz forces of the form F=J x B
Where F is a body force per unit volume, J is the induced dynamic current density, and B is the static magnetic induction. The most important application of EMATs has been in nondestructive evaluation (NDE)applications such as flaw detection or material property characterization. Couplant free transduction allows operation without contact at elevated temperatures and in remote locations. The coil and magnet structure can also be designed to excite complex wave patterns and polarizations that would be difficult to realize with fluid coupled piezoelectric probes. In the inference of material properties from precise velocity or attenuation measurements, use of EMATs can eliminate errors associated with couplant variation, particularly in contact measurements.

Normal Beam inspection in ultrasonic inspection

NORMAL BEAM INSPECTION:- Pulse -echo ultrasonic measurement can determine the location of a discontinuity in a part or structure by accurately measuring the time required for a short ultrasonic pulse generated by a transducer to travel through a thickness of material, reflect from the back or the surface of a discontinuity, and be returned to the transducer. In most applications, this time interval is a few microseconds or less. The two-way transit time measured is divided by two to account for the down-and-back travel path and multiplied by the velocity of sound in the test material. The result is expressed in the well-known relationship.
     d=vt/2 or v=2d/t
Where d is the distance from the surface to the discontinuity in the test piece, v is the velocity of sound waves in the material, and t is the measured round-trip time.

Precision ultrasonic thickness gages usually operate at frequencies between 500kHz and 100MHz, by means of piezoelectric transducer that generate bursts of sound waves when excited by electrical pulses. A wide variety of transducer with various acoustic characteristics have been developed to meet the needs of industrial applications. Typically, lower frequencies are used to optimize penetration when measuring thick, highly attenuating or highly scattering materials, while higher frequencies will be recommended to optimize resolution in thinner, non - attenuating, non - scattering materials.