NDT.net • Oct 2004 • Vol. 9 No.10

Advanced 3D tools used in reverse engineering and ray tracing simulation of phased array inspection of turbine components with complex geometry

Petru Ciorau Ontario Power Generation Inc. Pickering, Canada, peter.ciorau@opg.com
Wence Daks CadWire, Markham , Canada, wence@cadwire.com
Charly Kovacshazy, SITCO Precision Machining, Markham, Canada, charly@sitco.ca
Doug Mair Focal Point NDE, Missassauga, Canada, doug.mair@focalpointnde.com

Corresponding Author Contact:
Petru Ciorau, Email: peter.ciorau@opg.com


The paper outlines the practical aspects of reverse engineering and the integration of multiple pieces of software (Drafting, CNC Machining, Ray Tracing, Inspection Simulation Scenario and Phased Array UT Analysis), in order to inspect turbine components comprised of complex geometry. The CNC software, Mastercam, and design software, CADKEY/FastSURF®, were used to validate the phased-array automated and manual inspection of blade root, rotor steeples and disk-blade rim attachment. The integration of 3D part in the software engine, Imagine 3D and SimScan, as well as Tomoview analysis (specimen feature) is based on CADKEY Developer Kit - IGES/SAT file format. A generic Ray Tracing simulation for multi-probe beam was integrated into Imagine 3D. Representative examples of reference blocks and mock-ups, UT simulation and phased-array data comparison are presented.


Inspection and Maintenance Services (IMS) of Ontario Power Generation (IMS-OPG) was asked to develop phased array techniques and perform in-situ inspection of low-pressure turbine components (rotor steeples, blade roots, disk rim attachments) manufactured by different companies (GE, Alstom/ABB and Siemens/Parson). Lack of technical drawings led to reverse engineering of specific items and manufacturing of reference blocks and mock-ups according to IMS request. In order to demonstrate the coverage region and to set-up the focal laws for phased array techniques, a ray tracing model - Imagine 3 D and an inverse-forward inspection simulation - SimScan was developed and validated. Specific topics of this project were presented at different EPRI workshops (1-4) and NDT Conferences (5-8). This paper is an overview of the practical aspects of the integration of reverse engineering, simulation and UT data plotting under CADKEY® Developer Kit software package.

Reverse Engineering and manufacture of mock-ups

The purpose of the reverse engineering was to recreate blade/steeple mockups to match existing blades and steeples. The digitizing equipment was used to collect series of points on convex and concave sides. (see Figure 1a) The accuracy of digitizing was achieved at 50 m inch over 151 mm length. The collected point data was exported into Cadkey software. Cadkey is regarded as a premier modeling software that support ANSI and ISO standards and is extensively used for engineering applications (9). Lines, arcs and splines were used to create necessary geometry of cross section of convex and concave sides. Wire frame geometry was employed in Cadkey for solid model reconstruction. A tolerance-based curve-fitting algorithm located the patch boundaries according to surface curvature. Convex and concave sides were merged and precise replica of the digitized part was achieved (see Figure 1b). In order to communicate with other software, the Cadkey Solids part files were exported into SAT (ACIS), DXF and Parasolid file formats. Parasolid was imported into Mastercam software (10). CNC milling machines were used to reproduce all surface data. The inspection report indicated that tolerances of the manufactured parts were better then 0.1 of angular displacement and better then 25 microns of surface profiles.

Fig. 1: L-1 blade - Parson-type turbine: a) digitization points, b) solid.

The links between reverse engineering and other pieces of software are presented in Figure 2.

Fig. 2: The links between reverse engineering, CNC machining, UT simulation and UT data analysis, used in phased array inspection of turbine components.

Very complex parts could be digitized and recreated due to powerful solids modeling software. A 12-blade L-1 mock-up and a 3-blade Turbine end L-0 mock-up were designed and manufactured (see Figure 3 and 4).

Fig. 3: L-1 rotor steeple mock-up-ABB turbine: a) as solid file, b) on rotator.

Fig. 4: L-0 turbine end mock-up: a) solid file; b) machined.

Ultrasonic ray tracing, simulation and data plotting. A ray tracing model (Imagine 3D) in combination with a phased array inspection simulation (SimScan) was developed and validated. The SAT (ACIS) and DXF files resulted from reverse engineering is imported into I3D target file. The simulation was called for inverse-forward problem solving. Given specific defect location, SimScan could compute the probe trajectory, UT path, UT time of flight, refracted angle and X,Y, Z co-ordinates of defect and probe. This simulation helped ISD to validate all techniques and to reduce the number of reflectors into mock-ups and reference blocks. The model was validated within 1 mm UT path accuracy and 0.5° refracted angle. Probe trajectory was optimized based on simulation results. Examples of simulation are presented in Figure 5 and 6.

Fig. 5: Comparison between simulation and UT data for L-0 steeple-ABB-hook 5.

Fig. 6: Probe trajectory simulation for detecting defects on platform of L-0 blade.

The results are plotted into Imagine 3D and an Excel spreadsheet is generated for a variety of angles and defect positions (see Figure 7).

Fig. 7: Refracted angle and probe position for detecting defects at specific depths.

Cadkey could export DXF file into CIVA (11) for advanced simulation and defect parameter study. An example is presented in Figure 8 for detection of stress corrosion cracks in disk rim attachment and plotting B-scan in 2-D disk layout.

Fig. 8: Simulation of defect parameters for detection and advanced sizing in CIVA-Mephisto. Disk nr. 5 hook 3-GE low pressure turbine.

Cadkey could export the DXF file into Tomoview. The file is converted into 2-D specimen and the UT data are plotted for analysis and reported (see Figure 9).

Fig. 9: UT data plotting for detection and sizing of an EDM notch 6 x 2 mm on hook 3, using 2-D layout specimen generated in Tomoview through Cadkey DXF file.

Reverse Engineering of SCC and fatigue cracks. 3-D crack-like EDM notches and Phased Array Results In-situ inspection of ABB/Alstom and Parson/Siemens blade roots and rotor steeple detected stress corrosion cracks (SCC) and fatigue cracks (see Figure 10 and 11). Reverse engineering was used to machine 3-D crack-like EDM notches.

Fig. 10: Reverse engineering of SCC in row 10 blade [Parson] and phased array response.

Fig. 11: Reverse engineering of SCC in L-0 steeple [ABB] and OMNISCAN phased array response.


Reverse engineering based on Cadkey was used for multiple tasks to validate the phased array technology for in-situ inspection of low-pressure turbine components. Both manufacturing and simulation data are within acceptable limits. The UT results were plotted into 2-D layout generated by Cadkey/Tomoview import/export features. The UT results are within 2 mm space envelope tolerances. The link between Cadkey and Parasolid file format used by Mastercam in CNC machining speeded up the manufacturing process within 2-3 weeks for a very complex mock-up. Imagine 3D and Simscan software contributed to optimization of scanning pattern and the defect detection in most critical areas.


The authors wish to thank IMS Management-Ontario Power Generation Inc. for granting the publication of this paper.


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