• Each channel
• Each group of channels working at parallel

In the newly constructed gas and oil off-shore and on-shore pipelines the pipes are girth-welded automatically then rapidly inspected, coated, and buried. Detection, evaluation, and repair of defects in the welds should be performed very quickly in order avid the affecting of the construction cycle therefore the high-speed automatic ultrasonic testing (AUT) of girth welds is incredibly demanded as sole codes accepted alternative to radiography

AUT is implemented through scanning of the weld along the fusion line using several probes situated on the OD surface from both sides of girth weld. Traditionally the frame carrying the ultrasonic probes and position encoder is fitted into the traction unit (scanner) moving along the orbital travel band and the umbilical connects probes, position encoder, and scanner’s motor to ultrasonic pulsing-receiving, control, data processing and recording electronics, which is placed either in the truck cabin (on-shore inspection) or in a separate room on the lay barge (off-shore inspection) at the distance of up to few tens meters from the scanning deck. A team of the operators handles the AUT system: usually there are two operators (scantechs) involved into the placement of scanning stuff onto the pipe and one operator is responsible for control of the scanning, observation of the indications and recording process, and taking GO/NO GO decision

AUT of girth welds is regulated by a couple of codes such as ASTM E-1961, API 1104, DNV-OS-F101, and DNV-RP-F118, according to which the weld volume is divided into multiple horizontal thin slices (zones) in the cap, fill, hot pass, and root areas. The designated zones are insonified one by one through implementing of the sequence of independent pulsing-receiving shots. Use of phased array (PA) technology significantly minimizes quantity of probes involved into multiple zone insonification thanks to electronic beam steering. This simplifies scanning stuff and accelerates the inspection. Use of several TOFD and conventional probes simultaneously with PA probes provides complete coverage of the weld volume at every cross-sectional position along the fusion line: the PA probes do implement pulse echo and tandem technique for the detection of various compact and longitudinal defects; the conventional probes perform inspection for the detection of transversal defects (K- and X- schemes), detection of laminations in the heat affected zone in parent material, etc.; TOFD probes implement complimentary technology allowing detection of the compact and longitudinal defects through receiving of the diffracted signals. The ability of defect detection in each zone is provided through calibrating of the system on the specially manufactured Z-cut blocks containing certain number of artificial reflectors, which’s location, orientation, shape, and dimensions represent variety of flaws to be sensed and recorded

The practical use of the traditional PA AUT stuff over several years highlighted a number of inconveniencies experienced by the inspection providers:

• Big expensive, heavy, bulky, and vulnerable umbilical causing relatively high operational cost as well as low signal to noise ratio and high power consumption due to transfer of analogue signals through tens meters length wires
• Insufficient quantity of A/D converters leads to use of multiplexing and elevating pulse repetition rate further increasing power consumption
• Insufficient quantity of pulsing-receiving channels requires more than one scanning revolution and / or making compromise by using the wedges of PA probes also for TOFD to inspect single girth weld completely, this slows the overall speed of AUT
• Overheat of electronics caused by high power consumption requires water-cooling or frequent shutdown breaks during work shift

First introduced in 2007 ISONIC PA AUT system from Sonotron NDT represents cutting edge technology solution for high-speed AUT of girth welds bringing practical implementation to the highest convenience level

For the first time ever:

• the electronics of ISONIC PA AUT packed into rugged portable light weight (6.8 kg only) IP 67sealed case was fitted into the same scanner frame that carries the probes and encoders
• the regular remote PC connected to the instrument through Ethernet provides full control, data acquisition and imaging in real time, thus no big expensive, heavy vulnerable umbilical – just thin and very light weight armored tube carries DC wires and LAN cable, which are connected to the machine through the specially designed rotating terminal
• the probes signals are sampled and pre-processed in real time on-board; the digitized raw inspection data is transferred then to the to remote PC for further processing, storage, and imaging: fully digital through-Ethernet control and data transfer provide practically unlimited length of distance to the remote PC providing the flexibility of creating control rooms or multiple monitor stations throughout the barge / factory / weld station, etc
• the probes are connected to ISONIC PA AUT using short cables – comparing to transfer through long umbilical this provides much better signal quality significantly improving the signal to noise ratio and dynamic range
• Further improvement of the signal to noise ratio and dynamic range is achieved through firing probes with unique bi-polar square wave initial pulse reaching up to 300 Volt peak to peak for PA probes and up to 400 Volt peak to peak for the conventional and TOFD probes. The duration and amplitude for both positive and negative half-waves of the initial pulse may be tuned in wide range. Additionally it is provided high stability of firing amplitude settled by an operator whilst the leading and falling edges of bi-polar initial pulse are electronically boosted
• there is no limit for the quantity of PA probe elements composing emitting aperture – if necessary all elements of each PA probe connected to ISONIC PA AUT may fire simultaneously
• the advanced low noise design provides the ability of up to 100 dB analogue Gain for PA, TOFD, and conventional probes
• ISONIC PA AUT performs 16-bit 100 MHz sampling rate digitizing of signals obtained by all elements of receiving aperture at parallel independently on their quantity (aperture size) – there is no multiplexing involved; the digitized signals are phased (phase-shifted) and superimposed on-the-fly according to the desired focal law so each superimposed A-Scan is formed and memorized in the hardware buffer in real time during the entire pulsing-receiving shot (focal low)
• ISONIC PA AUT performs complete raw data capturing allowing play-back of all A-Scans obtained during the scanning; this provides full compliance with ASME 2235 Code Case related to the use of ultrasonic inspection in lieu of radiography
• the rational power management eliminates heating problem; thanks to extremely low power consumption there is no intake air, water or other type cooling is required for the ISONIC PA AUT
• in the ISONIC PA AUT each pulser receiver for TOFD and conventional probes may be operated in both modes – dual and single, i.e. use of dual element probes, TOFD insonification, K- and X-scheme for pitch-catch detection of transversal defects with shear waves, etc employ only one channel per task
• typically ISONIC PA AUT comprises 128 PA channels allowing simultaneous use of two 64-elements probes and 16 conventional channels, which are totally separated the from PA stuff; it is upgradeable to 4096 PA / 512 conventional channels functionality thanks to multiple units operation (up to 32) controlled from one computer. This unique feature might be useful for the future state of the art use, for example matrix PA technology allowing 3D beam steering vs today’s 2D

• Probe Definition dialogue for entering parameters of PA probes and wedges

• Weld Definition dialogue for selection of appropriate weld bevel from data base and entering related geometry and dimensions

• Zones Definition dialogue for "slicing" of weld volume, cap, hot pass, and root areas into zones to be insonified in each qualified position of PA probe:

• Ray Tracing dialogue for determining of zone-by-zone insonification scheme (pulse echo or tandem; incidence angles; emitting and receiving aperture; focal distance) and appropriate positions for PA probes from both sides of the weld (Upstream – Downstream)

Pre-scanning Routine – Stage 2: Ultrasonic Setup Wizard

Ultrasonic setup is performed on the specially manufactured Z-cut blocks containing certain number of artificial reflectors, which’s location, orientation, shape, and dimensions represent variety of flaws to be sensed and recorded. The calibration blocks are manufactured for each pipe diameter (OD), wall thickness (WT), weld bevel, etc. in a manner providing the detectability and recording of all artificial defects a single full or partial revolution scan along the hypothetic fusion line. Typically the calibration block is shaped as piece of pipe allowing setup of all scanning stuff; each cross-section section containing the artificial defect is marked on the OD surface of the pipe accordingly

The initial goal is one-by-one placement of the appropriate probe either PA, TOFD, or conventional into every predefined positions and providing the necessary settings (Gain, Gate, Aperture, etc) ensuring detection and resolving of all artificial defects. The process is illustrated by the short video and typical screenshots below:

A number of additional pulsing receiving shots should be calibrated for the PA and conventional probes with the purpose of the continuous coupling monitoring. For the PA probes ISONIC PA AUT allows using of the longitudinal wave back wall echo and / or the signal through-transmitted from one PA probe to another as a reference for the coupling monitor

The final screen of Ultrasonic Setup Wizard relates to the configuration of the strip chart. Strip chart is a way of AUT data presentation whereas each pulsing-receiving shot is continuously recorded into corresponding strip

ISONIC PA AUT allows forming the strips of the following types:

PE

Amplitude / TOF Pulse Echo Strip represents peak amplitude and time of flight for signals matching with Gate and exceeding it’s threshold level
Position of Amplitude Line on the strip is proportional to the signal height. Echo amplitude equal or exceeding 100% of A-Scan height brings Amplitude Line trace to full strip width level
Width of gray Time of Flight (TOF) Rectangle is proportional to the signal position in the Gate. For signals, which’s time of flight measurement point matches with the Gate end width of gray Time of Flight (TOF) Rectangle is equal to the full strip width
For geometry echoes matching within specially designated Gate Tail the Amplitude Line is not produced, just TOF Rectangle

MAP

Up to 256 Colors Palette Map Strip represents sequence of A-Scans whereas color of points for each horizontal line is coded according to corresponding signal level and default palette

TOFD

256 gray levels TOFD strip represents sequence of RF A-Scans whereas brightness of points for each horizontal line is modulated according to corresponding signal level

Coupling

Coupling Strip is formed through comparing amplitude of reference signal with the gate threshold. Green Sufficient Coupling record is provided for signals exceeding gate threshold; red Insufficient Coupling record is provided in opposite case

Reshaping of the Strip Chart is possible through manipulating position / lateral displacement of each strip according to the probes fitting into the scanning frame:

The Calibration Scan is performed then in the automatic mode in order to ensure the sensing and resolving of all artificial defects and recording them at the right positions

Ultrasonic Setup Wizard is completed with creating of the final Inspection Setup File; the routine inspection becomes possible at any moment since the said file is uploaded into control computer

The movies illustrating scanning of calibration blocks:











Note: In order to accelerate the data stream the videos above are linked to the Youtube. In case the YouTube may not be accessed from your location please use the links below