Implementation of Special PA UT Techniques for Manufacturing Inspection of Welds in Thick Wall Components 

 

 

Paper presented at the 11th International Conference on NDE in Relation to Structural 

Integrity for Nuclear and Pressurized Components, 

Jeju (Korea), May 19‐21 2015 

 

 

 

Implementation of Special PA UT Techniques

for Manufacturing Inspection of Welds in Thick Wall Components

Dirk Verspeelt 1, Dominic Marois 1, Guy Maes 1, Jean Marc Crauland 2, Michel Jambon 2, Frédéric Lasserre 3

1 Zetec, zNDT Solutions, Québec, Canada 2 AREVA Nuclear Power, Chalon / St Marcel, France,

3 AREVA Nuclear Power; Paris, France Abstract

The AREVA-NP/EFF/SAINT-MARCEL factory have selected advanced automated UT based on phased

array and TOFD techniques, in view of replacing manual UT and radiographic testing, for circular welds in thick-wall components. The principles of the applied phased array and TOFD examination techniques, and the on-site implementation will be briefly reviewed.

This paper will then address how special UT examination techniques are implemented using phased array technology, to complement the generic techniques.

Tandem configurations, using the LLT technique, are used to obtain enhanced detection capability on planar flaws perpendicular to the inspection surface. Both single probe and two-probe configurations are used to cover the complete wall thickness.

Asymmetric TOFD configurations (Delta technique), generated with phased array probes, are used to maximize TOFD coverage in areas where access is limited to one side of the weld.

For both techniques, theoretical considerations on probe design will be presented, as well as the practical implementation of the focal laws using the UltraVision® phased array calculator.

The performance of the special techniques will be illustrated with ultrasonic data from practical trials on representative specimens with artificial and realistic flaws. It will be shown how the UltraVision software supports comprehensive visualization of the data generated by the special techniques, and how the advanced tools allow for efficient data analysis.

Keywords: phased array, TOFD, weld inspection, reactor vessel

Manufacturing of Steam Generators (SG) and Pressurizers (PZR) involves non-destructive testing of the circumferential welds according to the French Design and Construction Rules for Mechanical Components of PWR Nuclear Islands (RCC-M) code. This includes surface and volumetric NDT methods.

The low alloy steel pieces of PZR and SG (Figure 1) are assembled by means of narrow gap submerged arc welds. The weld thickness range varies between 100 mm and 180 mm. Shell diameters varying between 3.077 m and 5.165 m yield weld lengths up to more than 16 m.

Historically, Radiographic Testing (RT) was applied before heat treatment while manual UT was used in complement for examination of the welds before and after heat treatment.

For productivity and environment reasons, the AREVA-NP/EFF/SAINT-MARCEL have decided to replace manual UT and RT by advanced automated phased array pulse-echo (PE) and TOFD techniques.

1. Introduction

Figure 1: Pressurizer (PZR) and Steam Generator (SG) weld outline

2.1. Generic Inspection Techniques In order to demonstrate the best possible equivalence between the current methods (RT and manual UT)

and the proposed alternative UT techniques (PE and TOFD), and instead of a qualification (very time consuming), the development of the new UT phased array PE technique was at the start based as much as possible on the existing manual UT characteristics [1],[2]. Figure 2 shows a schematic representation of the pulse-echo examination techniques that were selected. The phased array beam steering capability is used for reproducing the refracted angles required by the code (0ºLW, 45ºSW, 60ºSW and 70ºSW) while reducing the number of probes. In order to optimize the response for various defects orientations, the beam skewing capability is used to replace manual optimization (turning the probe) in conventional UT.

Figure 2: Weld coverage using beam steering and skewing with phased array pulse-echo techniques A typical inspection result from the pulse-echo techniques is shown on Figure 3. Since more than 90

pulse-echo beams are used (different beam orientations, refracted angles and skew angles), analysing the weld data beam by beam would require too much time. Therefore, the merge tool in the UltraVision software is used to calculate and visualize, considering all beams, the maximum amplitude found for each unitary volume of the inspected weld zone. The left view (VC-Side) shows a cross section of the weld with all indications found along the weld seam. The top right view (VC-End) shows a “front” view of the weld, whereas the lower right view (VC-Top) shows the top view of the weld.

2. Dedicated Advanced Automated UT System

Figure 3: Typical inspection result from pulse-echo techniques, using Merged Data from all beams

The TOFD technique is implemented using a combination of conventional and phased array probes (see Figure 4. The near-surface depth range is covered by two conventional configurations. The phased array probe set covers the deeper range. Besides a reduction of the number of probes, this allows for flexible adaptation of zone division to fit various weld thicknesses, and a good control of the beam spread for a given depth range resulting in a high signal-to-noise ratio (SNR) and reduced back-wall dead zone.

Figure 4: Depth zone coverage for TOFD inspection techniques The excellent SNR obtained with the phased array TOFD configuration is shown in Figure 5. The left

image shows the signals from an alumina insert, known to yield low diffraction amplitudes: the quality of the signal is very good and the obtained SNR is about 16 dB. The right image shows a 2 mm deep far-surface breaking notch in a 165mm test block. The back-wall dead zone is reduced to a minimum.

Figure 5: PA-TOFD images from an embedded 4 mm height Alumina insert (left), and a 2 mm height far-surface EDM notch (right)

2.2. On-Site Implementation A dedicated industrial system for the UT inspection during manufacturing of large narrow gap submerged

welds has been developed, and the manufacturing was finalized end 2013. It was commissioned in the factory in France in the spring of 2014 (see Figure 6). This system is used to deploy all inspection techniques discussed in the previous paragraph.

Figure 6: Dedicated automated UT system during commissioning in factory The system includes a dedicated 2 axis-scanner system with magnetic wheels, shown on the left image of

Figure 7. A detector on the scanner allows for the steering of 2 circumferential motors, to follow the trajectory projected by a laser tracking device onto the component. The axial movement is performed by a linear arm that carries the probe holder. The height of the linear movement allows travel over obstacles (nozzles), and the position of the legs can be adapted to move between obstacles.

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