To avoid unnecessary processes, minimise errors and operational conflicts, GE launched UltraScan™ Duo. Duo is different to other inline inspection (ILI) tools on the market as it features a new ultrasonic system that detects and sizes corrosion and cracks in the same run, using ‘phased array’ sensor technology, which has already been applied in medical and other fields.

The main advantages are:

• Control of ultrasound direction for metal loss and crack inspections in one run; • Sensor number, aperture and beam shape can be optimised for measurement tasks, with a high number of measurement channels resulting in high-resolution coverage of the entire wall circumference; and, • Special modes applicable for detecting small pits and cracks associated with corrosion, including stress corrosion cracking.

Due to extremely high measurement resolution (in axial, circumferential and radial direction), a very good probability of detection (POD) and sizing accuracy is achieved. These capabilities are crucial for long-term assessment of factors including corrosion growth analysis, inspection intervals, and for planning of maintenance and repair work.

Improvements over conventional ultrasonics

Conventional, ultrasonic non-destructive testing (NDT) relies on physical sensors as opposed to virtual sensors.

Conventional Technology

A sound beam’s general shape and direction are fixed for conventional sensors. For each application, an individual sensor must be arranged mechanically.

Phased Array Technology

With phased array, virtual sensors and firing patterns are programmable, enabling individual sensors to shoot in different directions and with different sound characteristics. For example, a smaller sound beam may be used for pitting inspection.

For inspections where conditions, including pipeline medium properties, are not clear during preparations, ILI settings can be left undefined until GE technicians arrive. As sound settings are performed via computer, there is no need for mechanical changes or manual calibration work on the sensors and sensor electronics.

Demonstrating the technology differences, for pitting inspection in a 24 inch pipeline, the Duo carrier can be programmed to use 675 virtual sensors, leading to a 3.3 mm circumferential resolution.

Dual Mission

Conventional ultrasonic sensors only carry out single missions (either wall thickness or crack measurement). Duo’s virtual sensors allow a wide range of inspections, independent or combined.

Detection Capabilities

Regulations now require more detailed pipeline integrity programs. Phased array can detect even smaller cracks and metal loss. For example, stress corrosion fields and single cracks with a minimum of 25 mm can now be detected with Duo.

Wall thickness determination is more reliable since beam width and circumferential resolution can be adjusted. This leads to better pitting corrosion detection and measurement, overcoming a major shortcoming of conventional ultrasonics.

Ultrascan DUO Operating principle

UltraScan Duo’s phased array technology consists of arrays featuring elements controlled individually by ultrasound electronics. The way these elements are triggered determines sound type and path.

Neighbouring sensor elements triggered simultaneously generate a perpendicular pulse. If neighbouring sensors are triggered with a certain time shift from element to element, an angular pulse is generated.

For ultrasonic measurement of a wall, Duo’s sensors are guided along the wall. Ultrasound electronics activate a virtual sensor in the desired direction. For crack detection (angular beam), the sound wave propagates through the liquid and is then coupled into the wall, where it continues propagating.

With a crack, part of the sound is reflected and received by the same sensor. The crack’s position is calculated using the time-of-flight of echoes.

The Duo’s sensor carrier consists of two or more sections with phased array rings (the number of arrays depends on pipe diameter). The arrays are arranged so each covers a certain section on the circumference, including minimum overlaps with neighbouring arrays.

During Duo’s development, a significant number of trials at a 250 m loop testing facility built at GE’s site in Stutensee, Germany validated the measuring system’s functional performance.

First field inspection

The first Duo was designed for 24 - 42 inch lines. In March 2005, it was first launched into a 24 inch oil line for RRP/RMR (Holland). This line was inspected in 1992 with UltraScan WM (metal loss inspection) and 2002 with UltraScan CD (crack inspection).

In Germany, the phased array was programmed for individual inspections, including the type of coupling liquid used for an inspection. Electronics were checked by functional and continuous tests.

The inspection was conducted in Duo mode (combined corrosion and crack detection) at about 1.3 m per second. Post-run, Duo was received in perfect mechanical condition and connected to a PC to assess data quality.

The data allowed GE to optimise Duo’s shot sequence and improve onboard algorithms and data analysis software. To prove Duo’s capabilities, defects known from previous runs were used as a baseline.

Inspection results

Offline analysis of the data from more than 100 km showed excellent ultrasound data quality for metal loss and crack detection. The repeatable nature of ultrasonics allowed a detailed comparison between corrosion and crack data obtained by Duo to that collected with UltraScan WM and UltraScan CD.

The measurement principle is based on time-of flight computation of the whole echo peak set - that is, the A-Scan - received after firing a pulse against the wall. This technique allows GE to evaluate echoes with higher confidence than conventional processes.

The A-Scan technique enables direct measurement of wall thickness down to a lower limit of about 1 mm with a resolution of less than 0.1 mm. The same resolution applies for the whole measurable wall thickness range up to 37 mm. Crack inspection is possible up to 16 mm thickness with the present measurement configuration.

UltraScan Duo represents a major achievement using similar phased array technology that GE Healthcare employs to enhance diagnostic imaging and save lives. This allows operators to detect both cracking and metal loss in a single run, saving time and money while delivering the data needed to ensure pipeline integrity.