Automatic Ultrasonic Inspection of Steel Catenary Risers With a Corrosion-Resistant Alloy Layer
- Jan van der Ent (RTD Group) | Jacq van Nisselroij (Shell Global Solutions) | Frans Kopp (Shell Intl. E&P BV) | Andries Otter (Shell Sarawak Malaysia) | Nwoji Weli (Shell E&P) | Steve Judd (Acergy)
- Document ID
- Society of Petroleum Engineers
- SPE Projects, Facilities & Construction
- Publication Date
- June 2007
- Document Type
- Journal Paper
- 1 - 8
- 2007. Society of Petroleum Engineers
- 4.2.3 Materials and Corrosion, 7.3.3 Project Management, 4.1.2 Separation and Treating, 4.2.2 Pipeline Transient Behavior, 6.1.5 Human Resources, Competence and Training, 4.2 Pipelines, Flowlines and Risers, 4.2.4 Risers, 4.1.5 Processing Equipment, 6.5.2 Water use, produced water discharge and disposal, 1.2.3 Rock properties, 4.5.3 Floating Production Systems
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Corrosion-resistant alloy (CRA)-clad pipelines have austenitic girth welds. Such girth welds cannot be inspected by conventional ultrasonic methods and must to be examined by the nonconventional angle beam compression wave/creep-wave technique. Because of the dynamic nature of steel catenary risers (SCR) used in deep waters, very tight acceptance/rejection criteria apply.
This paper gives background information about the design and installation of SCRs, the material properties of such a design, and the inspection solution developed to examine such welds. In addition, the development and qualification as used in the Bonga project is demonstrated, and conclusions and recommendations are given.
The eight production and two water injection SCRs connecting the Bonga floating production storage offloading (FPSO) facility with the seabed at 1,000 m depth each contain approximately 100 m of CRA-clad pipe at the touchdown point (TDP) (Fig. 1.) The girth welds joining these clad pipes are of an austenitic nature with a coarse-grain structure when compared to the ferrite grain structure of girth welds in carbon steel. This coarse structure complicates inspection of the welds by conventional automatic ultrasound testing (AUT) [including time-of-flight diffraction (TOFD)], especially in view of the tight acceptance criteria for those TDP welds that are subject to fatigue-loading conditions.
The Bonga flowlines and risers contract was executed by Acergy on behalf of Shell Nigeria Exploration and Production Company (Snepco) (operator) and its coventurers Esso Exploration and Production Company Nigeria, Nigeria Agip Exploration, and Elf Petroleum Nigeria. The license holder for the Bonga field is the Nigerian National Petroleum Corporation (NNPC).
In parallel to the onshore double and quadruple joint production welding, a new automatic ultrasonic inspection method has been developed for austenitic pipeline girth welds.
This method uses dual-crystal focused-angle beam compression and creep-wave probes to cover the entire SCR CRA weld volume, including the clad layer.
In addition, the TOFD technique has been used to increase the overall inspection integrity and to detect and size root concavity. This approach also has been applied to offshore welding as well.
Throughout the progressive qualification process, onshore as well as offshore, it has been verified that the CRA inspection technique developed by Shell Global Solutions International and Röntgen Technische Dienst (RTD) adequately detects and qualitatively sizes the weld imperfections that also have been observed in, microscopic (destructive) evaluation.
The primary and coincidence inspection method has been demonstrated to be very versatile in comparison with conventional shear-wave tandem techniques. The technique is able to cover austenitic welds between
- Overlay-clad components
- CRA-clad pipe joints
- CRA-clad pipe joints and overlay-clad components
Besides the 10 SCRs with CRA-clad pipe [approximately 550 welds onshore in 1G (see Fig. 2) and 66 offshore in 2G (see Fig. 3)], the presented CRA inspection technique was used on more than 1,000 offshore CRA welds on the water injection flowline system. The Bonga field has been in production since 25 November 2005.
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