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loss defects, and is becoming widely accepted as a valid means of assessing the condition

of pipes and pipelines, particularly where they are difficult or expensive to access for

inspection. Today it is broadly applied in identifying corrosion in different situations in

pipes diameter range 50 mm to 1200 mm and for assessment of pipes state.

A non-contacting ultrasonic probe, placed inside a pipe, which operates in light liquid

product lines, can be realized as a movable test system. It is known as a pipe-inspection-

gear (PIG). The ultrasonic head comprises a fixed centrally mounted ultrasonic probe

whose signal is projected along the pipe axis on to a 45

angle reflector rotating at speeds

up to 1000 rpm. The forward speed is in the range of 1 m to 3 m per minute. The signal is

transmitted through the liquid to and from the outer pipe wall. The return signal is captu-

red for subsequent analysis. PIG can pass through a 1.5D bends (D is pipe outside

diameter) and can be pulled back to its launcher or move in free mode (autonomous

device for detecting flaws and leakage in pipes). With the captive PIG the power is

supplied along the umbilical and results returned on line. Such test systems can be used in

pipeline for transporting natural gas. They are exposed to aging, and the integrity has to

be monitored frequently. Stress corrosion cracks (SCC) can be easily detected using

liquid fluorescent magnetic particle inspection. However, this technique is not practical

for in-line inspection of pipes. Up-dated technology for pipeline inspection uses the MT

is capable to measure the local changed magnetic field on the inside pipe wall using

sensors. It is required that in-line inspection technology enables to locate the flaws

without having to resort to excavation. SCC is usually oriented along the pipe and may

remain undetected. It can occur in a range of pipeline field conditions including soil type,

stress, cathode potential, coating conditions and temperature. Axial magnetic field in-line

inspection PIG, extensively used for pipeline inspection, is convenient for detecting

corrosion damage or circumferentially oriented defects inside a pipe, but not surely flaws

or cracks in the axial direction. For that EMAT is better. Two EMATs can be used in the

pitch-catch disposition to send and receive longitudinal or shear waves perpendicular to

the longitudinal weld joint. EMAT is a vital NDT tool for an early location of SCC and

other defects, like corrosion, welding cracks, pits. It is important that such NDT tool is

capable to detect SCC accurately, without false signals, to characterize to some extend the

defect size. Although EMAT is in use for more than a decade, some further research work

is still necessary. Properly designed, EMAT can be positioned anywhere inside the pipe,

in a way that can send and receive confined acoustic waves for detecting flaws and

leakage in pipes.

Long range ultrasonic testing is also applied for detection of circumferential cracks

under the supports of long tubes in heat exchangers, inspection of railroad tracks, espe-

cially welded rails, inspection of wire cables and piping at pipe supports.

The next UT method in use is the phased array inspection. It is an advanced technique

for volumetric assessment and flaw detection, applicable for discontinuity detection in

thick steel plate or vessels, longitudinal and butt weld testing, stress corrosion cracking in

pipes and in turbines, nozzle corrosion testing, and hydrogen induced cracking.

. Phased array consists of a number of ultrasonic elements arranged in a single

instrument. The multiple elements are used to create an ultrasonic beam. The beams can

be “steered” to optimize their orientation to the tested object, increasing the probability of

detection of flaws, for example in longitudinal welds in piping. The beams can be

scanned over the object in order to produce an image. By adjusting the individual