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External Non Destructive Testing / Pipe work condition assessment API offers the latest technology to scan external pipe work assets; from this we can measure internal/external pit depths, wall thicknesses, ageing and corrosion levels. Utilising a specialist assessment system, an ultrasonic delivery driver is attached to the pipeline, the site technician measures the pipe circumference.
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Paper published in Inspectioneering Journal, September 2004.LRUT for the in-service surveying of metal loss in pipelines and piping was introduced by Plant Integrity (Pi) Ltd in the form of the Teletest ® in 1998. Pi is a subsidiary of TWI (formerly The Welding Institute) and provides a commercial outlet for TWI's technologies.The impetus for the development of LRUT is that ultrasonic thickness checks for corrosion, erosion, etc. Are localised, in that they only measure the thickness of the area under the UT transducer.
The operation of the LRUT technique is shown schematically in Fig.1. Teletest ® uses low frequency guided ultrasound travelling along the pipe providing 100% coverage of the pipe wall.Up to 350 metres of pipework can be inspected from a single test point (using a battery- or mains-power supply). LRUT reduces the costs of gaining access and avoiding extensive removal of insulation (where present). The whole pipe wall is tested, achieving a 100% examination (including areas such as at clamps, and sleeved or buried pipes). Continuous developmentOver the past decade, the development of LRUT has been funded through a variety of sources including most recently, the Pipeline Research Council International, for the application of LRUT to large gas transmission pipelines.The equipment can now generate any of the three main long-range wave types (longitudinal, torsional and flexural). It uses phased-array technology making it possible to focus ultrasound at any point both along and around the pipe).
The inflatable collars and multi-mode transducer modules increase its high temperature capability to 160°C. Inspection sensitivityThe earliest work showed that the smallest area of metal loss which LRUT can detect is approximately 3% of the pipe wall cross-section. The reporting level which is normally used is a signal amplitude equivalent to 9% area, to ensure that false call rates are kept to an acceptable level. These thresholds were verified through 'blind trials' without knowledge of any defects and the results were independently evaluated.Figure 3 shows the results from the Teletest ® technique on 36 individual defects. The plot is in terms of depth and circumferential extent of the defects and indicates whether each was detected or not. The lines representing 3% and 9% defect area are also included.
The data show the classic probability of detection characteristics, with an increasing likelihood of detection above the 3% level. All flaws at or greater than the 9% reporting level were detected.
The main factors which affect the sensitivity of LRUT are:. The size of the corroded area, as 'seen' by the wave propagating along the pipe. Detectability is related to the proportion of the pipe wall cross-section which is lost (the combination of the depth and the circumferentialextent). The axial extent of the corroded area.
The technique is less sensitive to this dimension, although long defects produce a stronger signal than shorter ones. Pipe features. All discontinuities affect the ultrasound signals and therefore give rise to responses, such as butt welds, bends, attachments, etc. Coatings.
Some types of coating affect the rate of attenuation of the ultrasound and therefore reduce the test range achievable. Test sensitivity. To perform an adequate test, a certain level of ultrasound has to be generated (a minimum signal-to- noise ratio), in order to maintain the expected sensitivity to defects.14' Ammonia line case studyThis line was the feed to a reactor vessel in a chemical complex and was insulated, so external corrosion under insulation (CUI) was suspected. It emerged from the reactor around 2m above ground level, ran vertically for around 7m then horizontally for a further 10m. The Teletest ® A-scan output is shown in Fig.4. 10' Buried line case studyThis Teletest ® survey was carried out on a network of water injection lines at an oil processing facility. The concerns were external corrosion around the soil to air interface and where the coating had been damaged in the underground sections.
Several locations were identified on the A-scan output as being moderate-to-severe defects and were excavated. At one location, the line was found to be so heavily corroded that repairs were immediately required, Fig.6. It's unlikely that this defect would have been detected by other means before it had caused a failure of the line. SummaryThe growing body of evidence for the performance of LRUT in general and Teletest ® in particular, is supporting the wider application of this novel technology. LRUT has already crossed the technology transfer threshold from a curiosity to a usable and highly effective tool.
It is particularly useful for locating corroded areas that may then by conventionally sized for fitness for service assessments. In many situations, it is a vital tool for inspection engineers to hold in their arsenal of NDT techniques.
Girth Weld Inspection SystemThe PipeWIZARD 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 veryquickly.Automated Ultrasonic Testing (AUT)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. Conventional UT:Complete coverage with 24 probesIllustration showing the inspection of one zone. With conventional UT technology several probes are needed to cover all zones.Codes ComplianceIn 1998, the ASTM published the E-1961-98 code (reapproved in 2003), which covers key elements of AUT of girth welds - zone discrimination, rapid data interpretation, specialized calibration blocks, and configuration procedures. The E-1961 code is designed for ECA.
Similarly, in 1999, the American Petroleum Institute (API) published the 19th edition of Standard 1104, which covers mechanized ultrasonic testing and radiography of girth welds.PipeWIZARD allows inspections to comply with the ASTM E-1961 code, and by inference, with the API 1104 standard. It also allows compliance with the DNV-OS-F101 standard, the offshore AUT code.Company specifications may exceed the codes, typically by asking for improved sizing or better resolution.PipeWIZARD ExperienceThe PipeWIZARD system is specially designed to work in extreme environments, from cold Siberian regions to hot Middle-East deserts; in humid, salty or dry conditions. Extensive tests have been also performed to ensure the PipeWIZARD capability to resist to vibrations, shocks, and electromagnetic interferences.PipeWIZARD fits all configurations of circumferential welds:. Any type of weld profiles: CRC-Evans, J-bevel, V-bevel, double V, X, etc. Typical pipe wall thickness: from 6 mm (0.25 in.) to more than 35 mm (1.4 in.)Options are available for thicker pipes. Typical pipe diameter: from 6 in. ScannerThe PipeWIZARD scanner is a compact, robust, field-proven unit offering stable and repeatable scans.The scanner head is designed for IP66 rating and houses a driving motor, an encoder, two phased array probes and wedges, two TOFD probes and wedges, and one temperature sensor.An heavy-duty umbilical cable shields all necessary cables, it also includes the water line for coupling.Computer and SoftwareRuggedized laptop with Microsoft Windows and PipeWIZARD data acquisition and analysis software installed.
Software package includes: TomoView and Advanced Calculator software, Microsoft Office, and all necessary software accessories.Instrumentation BoxThe instrumentation box is a compact, ruggedized, designed for IP64 rating, heavy-duty housing for the TomoScan FOCUS LT and the PWZ-MCDU. It is equipped with a heat exchanger mounted on the front cover and internal shock absorbers for equipment protection.
An external power outlet is available on the connection panel to connect accessories.Acquisition UnitThe acquisition unit, a TomoScan FOCUS LT 64:128, offers up to 64 focusing channels and 128 P/R for multiple combinations of phased-array and conventional probes.Motor Controller and Drive UnitThe PWZ-MCDU drives one DC servo motor using an Ethernet link.