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Phased array ultrasonic testing of nozzle joints

TWI partnered with EDF, ENSA, ESKOM and PETROBRAS for a 24-month joint industry project to develop portable field-implementable phased array ultrasonic testing (PAUT) equipment for the inspection of nozzle joints. TWI’s first activity in the project was to undertake a review of the marketplace and technology development institutions, to identify available technologies that satisfied the project specifications. Following the review TWI chose to work with three main PAUT equipment suppliers to develop and evaluate a number of potential solutions.

The first company TWI approached was Olympus NDT, which had already developed a prototype system that optically established the position and orientation of the phased array ultrasonic probe and plotted the inspection data from within the nozzle joint in real-time for operator assessment. TWI also worked with Phoenix ISL, to develop a unique three-axis manually encoded scanner for use by operators in the field. The scanning system was able to record the position and skew orientation of the phased array probe mechanically – information which was then used by a new module developed by M2M for its portable Gekko instrument to plot the inspection data in a 3D volume of the component for interpretation by the operator while in the field.

For each of the two systems TWI generated procedures and undertook an inspection capability evaluation following ENIQ (European Network for Inspection and Qualification) guidelines to provide a capability statement for inspection of nozzle joints.

Inspection of complex shapes

TWI generated a generic methodology to address the fundamental technical requirements of complex-shaped components inspection. The two different prototype systems were compared against this methodology to verify which aspects were met. This document remains an important resource for addressing not just nozzles but a number of other three-dimensional complex-shaped components, such as elbows in pipework.

TWI also identified several enabling technologies for further development, including the use of membrane wedges, which was implemented as a research and development activity during the project.

A key requirement was to ensure that the inspection techniques were compliant with current governing standards and codes. TWI identified several suitable standards for implementing PAUT and for interpreting the signals. Indications were characterised as either volumetric or planar, with the latter being rejectable regardless of any other aspects. This made the inspection conservative and ensured that the joint fabrication was as high in quality as possible, detecting any serious threats to integrity for those components in-service.

Fig 1. Phoenix ISL scanner on a test specimen and M2M Gekko instrument displaying data from within the nozzle joint
Fig 1. Phoenix ISL scanner on a test specimen and M2M Gekko instrument displaying data from within the nozzle joint

Selecting suitable software

It was recognised early in the project that to accurately address the inspection problem three-dimensional design tools would be essential. The Zetec UltraVision 3D ultrasonic software package was selected for the design and verification of the methodology. This tool allows the user to input the critical flaws in different parts of the nozzle joint and select the most suitable beams from a phased array probe to detect them. This was validated experimentally during the project and shown to be a viable route for designing the inspection techniques.

TWI evaluated the generic methodology using the two prototype systems from Olympus and Phoenix/M2M, using a different TWI-developed procedure for each. The ENIQ approach of identifying the essential parameters was followed to provide a capability statement for inspection of the nozzle joints. TWI specified two specimens containing flaws for this assessment, which were fabricated by Sonaspection.

Hands-on testing and validation

Qualified PAUT Level 2 operators followed the procedures and reported on the specimens, providing an independent assessment of the systems’ capability and performance. This exercise was also a valuable way to identify practical issues which could then be reported back to the suppliers to help them develop their inspection products.

TWI compared the experimental findings with simulations created using the CIVA software package to build a technical justification for the use of PAUT for inspection of nozzle joints. This document is important to ensure that end-users can rely on the inspection results and also, crucially, be aware of the method’s limitations, so it can be effectively and confidently used in industry.

TWI completed the project by sectioning one of the specimens to verify the presence of the flaws and additional indications found by the inspection. The second specimen was retained to aid technology transfer activities and for demonstrations to TWI Members. The specimen is also being used for training of operators and TWI is presently working on developing bespoke training programmes for TWI Members who wish to implement PAUT of their nozzle joints.

The prototype systems, which continue to be refined by the suppliers, are now available for commercial acquisition.

For more information on the system, or to register your interest for the bespoke PAUT inspection of nozzles training, please email contactus@twi.co.uk.

Fig 2. Design of three-axis manual encoded scanner for nozzles
Fig 2. Design of three-axis manual encoded scanner for nozzles
Avatar Channa Nageswaran Technology Consultant

Channa undertakes research and development into ultrasonic techniques for application to address a range of critical issues in industry. This includes inspection of austenitic, coarse grained welds, early-stage detection of damage such as type IV creep cracking and high temperature hydrogen attack, and development of high temperature inspection solutions.

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