The Complete Solution: Combined Crack and Metal Loss Detection Tool using Phased Array Technology By A. Hugger, J. Franz, H. Charbon, R. Bauernschmitt, M. Tschuch, K.-H. Käshammer, I. Lachtchouk, J. Ehrhardt. GE Oil & Gas, PII Pipeline Solutions March 2007 INTRODUCTION Pipeline operators face many threats to the integrity of a pipeline. Over the years, sophisticated equipment and methodologies have been developed to counter these threats. However, until today, operators have been using individual inspection tools to detect and measure specific defects such as corrosion or cracks. This has caused operators around the world, to invest significant efforts to perform multiple inspection runs and later correlate independent sets of inspection data. In order to avoid these unnecessary processes and to minimize sources of error and operational conflicts, GE launched a new inline inspection tool UltraScan DUO. This tool is not merely another inline inspection tool, it is different from any inspection tool already introduced into the market. This development consists of a state-of-the-art ultrasonic system that detects and sizes both corrosion and cracks in the same run with enhanced capabilities in both areas using Phased Array Technology, already successfully applied in other fields such as medical applications. The main advantages of this technology are: Direction of the can be controlled by the electronics, allowing to inspect for metal loss and cracks in one run. Sensor number, aperture and beam shape can be optimized for the measurement task. A high number of measurement channels results in high-resolution coverage of the entire pipe wall circumference. Special modes are applicable for the detection of small pits and of cracks associated with corrosion, e.g. SCC (Stress Corrosion Cracking). hits the metal loss contour metal loss with SCC hits the corners of the SCC cracks hook crack hits the horizontal part of the crack pipe wall hits the corner of the crack Detecting and identifying metal loss with SCC and hook crack Due to the extremely high measurement resolution (in axial, circumferential and radial direction) a very good POD (probability of detection) and sizing accuracy are achieved. These capabilities are crucial for any long-term pipeline assessment activities, e.g. corrosion growth analysis, planning of maintenance and repair work and of inspection intervals. IMPROVEMENTS OVER CONVENTIONAL ULTRASONICS Conventional ultrasonic Non Destructive Testing (NDT) relies on the use of "physical" sensors as opposed to "virtual" sensors. Conventional Technology: The general shape of a sound beam and its travel direction are fixed for each sensor in the conventional technology. This means that for each application an individual sensor arrangement must be provided mechanically. If the measurement conditions are changed, a different mechanical solution for the sensor carrier including a new selection of suitable sensor types is necessary. Conventional sensor carrier s: Crack Detection Phased Array Technology: Metal Loss inspection With Phased Array Technology, virtual sensor arrangements and firing patterns are programmable. This enables the individual virtual sensor to shoot in different direction and with different sound beam characteristics, e.g. smaller sound beam for pitting inspection. UltraScan DUO sensor carrier For inspection jobs where the measurement conditions like the pipeline medium properties are not clear during the job preparation phase, the ILI tool settings can be left undefined until the arrival of the GE technicians onsite. As the sound beam settings are all performed via computer interface, there is no need for mechanical changes on the sensor carrier or manual calibration work on the sensors and sensor electronics. To demonstrate the difference to conventional technology: for pitting inspection in a 24" pipeline, the UltraScan DUO sensor carrier can be programmed to use 675 virtual sensors. This improves the circumferential resolution from 8 mm (i.e. 1
the conventional case) to 3.3 mm. Dual Mission: Physical sensors used by conventional ultrasonics can only carry out a single mission that is either wall thickness or crack measurement. The use of virtual sensors allows the tool to inspect under the same configuration a multitude of missions whether independent or combined. Detection Capabilities: During the past ten years, regulations and national codes have evolved requesting more detailed integrity programs for pipeline systems. As a result, operators have the need to maximize the information they get from each inspection at acceptable cost. Hence improving detection capabilities has been raised in many worldwide forums. The use of phased arrays allows flexible programming of the virtual sensors to detect cracks, e.g. stress corrosion fields and single cracks with a minimum length of 25 mm. Wall thickness determination is more reliable since the beam width and circumferential resolution can be adjusted individually with Phased Array Technology. This also leads to better detection and measurement of pitting corrosion, thus overcoming one of the major physical limitations of conventional ultrasonic systems. OPERATING PRINCIPLE OF ULTRASCAN DUO The UltraScan DUO uses Phased Array Technology. The central items of this technology are arrays built-up of sensor elements which are controlled individually by the ultrasound electronics. The way that these sensor elements are triggered determines the kind of sound beam that is generated and the direction in which the sound pulse travels. thickness measurement (WM) sensor built-up by a group of sensor elements. If a set of neighboring sensor elements is triggered with a certain time shift from element to element, an sound pulse is generated. The direction of this sound pulse depends on how the time shifts increment. The right part of figure1 shows a "virtual" crack detection (CD) sensor built-up by a group of sensor elements transmitting under an angle of 17 in clockwise direction. For the ultrasonic measurement of a pipe wall, the Phased Array is guided along the internal surface of the pipe wall in a constant stand-off distance: sound path if no crack is present Left: No reflected echo signal in "clean" pipe sensor arrays crack pipe wall sound path if a crack is present Right: Signal echo from crack A virtual sensor is activated by the ultrasound electronics to shoot in the desired direction. In the case of crack detection with sound beam, the sound wave propagates through the liquid and is then coupled into the pipe wall where it continues to propagate (left part of the Figure above). If a crack is present in the pipe wall, part of the sound energy is reflected and received by the same virtual sensor (right part of the above Figure). The position of the crack within the pipe wall is calculated using the time-of-flight of the signal echoes. The sensor carrier of the UltraScan DUO tool consists of two or more sections with rings of Phased Arrays (number of Phased Arrays depends on the pipe diameter). direction of sound beam 17 direction of sound beam wavefront wavefront Coverage of pipe circumference with three sensor carrier sections phased array of composite sensor elements for wall thickness measurement Perpendicular beam for wall thickness measurement phased array of composite sensor elements for crack detection Angular beam for crack detection If a set of neighbouring sensor elements is triggered simultaneously, a sound pulse is generated. The Figure above (left part) shows such a "virtual" wall The Phased Arrays on the sensor carrier sections are arranged in a way that each array covers a certain section on the circumference including minimum overlaps with the neighbouring arrays. LOOP TESTING During all development phases of the UltraScan DUO tool, a significant number of trials were performed in order to validate the functional performance of the measuring 2
system. For this purpose a 250m long loop testing facility had been built at the premises of the pipeline solutions business of GE in Stutensee/Germany. As part of the validation the following was verified: Artificial defects with typical dimensions were systematically checked whether they were detected and sized correctly. The representation of the anomalies detected with the new UltraScan DUO tool was compared with the representation produced by other ultrasonic measurement systems. Main focus was concentrated on the repeatability of the measurements. The algorithms for building-up the virtual sensors, related shot sequences, the algorithms for the online digitization of the A-Scan and the related data extraction and storage were optimized. Finally, the procedures for the offline data pre-processing for making the measured ultrasonic data interpretable with the new display programs were optimized. Some examples from the test loop: External artificial notches, 25 mm long, 0.5-5 mm deep: in Europe. In September 2005, a 34" crude oil pipeline in North America was inspected. Both lines had already been inspected before with the UltraScan WM (metal loss inspection) and with UltraScan CD (crack inspection). The phased array ultrasonic sensor system was set up and programmed according to the individual inspection requirements, especially with regard to the type of coupling liquid used for the inspection runs. The inspections were conducted in the DUO mode (this is a combined corrosion and crack detection). Immediately after the inspection runs, the tool was connected to a PC to readout the diagnosis data from the mass storage unit to assess the quality of the data. The tool was received in perfect mechanical condition. USDUO Receiving Operations The inspection data allowed GE Pipeline Solutions to optimize the shot sequence of the ultrasound sensors and to further improve both the onboard algorithms and the data analysis software. Valuable operational experience was acquired during the runs. To prove the inspection capabilities of the UltraScan DUO tool, a number of defects in the pipeline already known from previous inspection runs were taken as a basis for a thorough data analysis. External artificial metal losses, ø30 mm, 1-9 mm deep: INSPECTION RESULTS The offline analysis of the measured data collected during both inspection runs showed that the ultrasound data quality was excellent for metal loss detection as well as for crack detection. The repeatable nature of Ultrasonic allowed a detailed defect comparison between corrosion and crack data obtained with UltraScan DUO to that collected with UltraScan WM and UltraScan CD. The ultrasonic measurement principle of UltraScan DUO is based on the time-of flight computation of the whole set of signal echo peaks - i.e. the A-Scan - received after firing a ultrasonic sound pulse against the pipe wall. This A-Scan analysis technique allows GE to evaluate the ultrasound signal echoes with higher confidence than conventional measurement processes. FIELD INSPECTIONS IN 2005 The first UltraScan DUO generation was designed for the inspection of 24" to 42" pipelines. In March 2005, the tool was launched for the first time into a 24" oil product pipeline 3
This A-Scan shows the entry echo and 11 repeated rear wall echoes of the bottom of a deep external metal loss The A-Scan analysis technique applied with the UltraScan DUO enables the direct measurement of the pipe wall thickness down to a lower limit of approx. 1 mm with a resolution of less than 0.1 mm. The same resolution applies for the whole measurable wall thickness range of up to 37 mm. Crack inspection is possible up to 16 mm wall thickness (with the present measurement configuration). The A-Scan shown in the Figure above belongs to the deepest point of the metal loss example detected by the UltraScan DUO as shown in the next Figure. These are C- and B-Scans of an external metal loss in a 34" pipeline. The metal loss in the UltraScan DUO representation seams to have a greater width - the reason for that is the larger number of sensors and, following, a better circumferential resolution. 34" US-CD 2005 34" US-DUO 2005 24" US-WM 1992 24" US-DUO 2005 The C-Scans at the top show the area of an external metal loss. In the B-Scans below, the depth contour of the metal loss at the cursor location is visible. The UltraScan DUO worked with a lower detection threshold. This effect implies that more "grey color" is displayed. 34" US-WM 1992 (top) 34" US-DUO 2005 (bottom) The two representations show a single, external crack at the longitudinal weld. The amplitude pattern are very similar in both measured data. 34" US-CD 2005 34" US-DUO 2005 4
This is also an external crack at the longitudinal weld. The characteristics of the ultrasound echoes from the crack are significantly similar. However, the amplitude heights of the UltraScan DUO's echoes are generally stronger than the amplitudes of the UltraSan CD. 34" US-WM 1992 34" US-DUO 2005 These C-Scans show an area with laminations. It seems that the laminations have remained their shape since the first inspection in 1992. CONCLUSION AND OUTLOOK The introduction of UltraScan DUO represents a major technical achievement. The UltraScan DUO uses phased array ultrasonic technology similar to that GE Healthcare employs to enhance diagnostic imaging and to help to save lives. This revolutionary technology allows pipeline operators to detect both cracking and metal loss in a single inspection, saving time and money in the process. Building on the reliability and accuracy of the traditional ultrasonic suite, UltraScan DUO offers industry-best crack detection capabilities, and improves both detection and measurement of pitting corrosion. It delivers the high-resolution data that operators need to ensure the integrity of their pipelines. UltraScan is a trademark of PII Limited 5