Session: 04-01: Emerging Techniques & Technology

Paper Number: 130993

130993 - Ultrasonic Corner Wave Imaging for Crack Characterization in Nozzle-to-Vessel Welds 

Abstract: 

The ultrasonic non-destructive testing (UNDT) of nozzle welds is a major concern for the pipeline and vessel industry. However, the saddle geometry varies along with movement of the probe, leading to complicated ultrasonic propagation such as beam skewing and splitting. Hence, the image result is poor in flaw characterization. Current technique utilizes the beam skew capability of 2D matrix probe to perform inspection from the vessel side with the aid of a three-axis mechanical scanner containing three encoders.  This mechanism is too complex and requires high-performance equipment and software to realize real-time positioning of flaws. Therefore, a convenient inspection and imaging solution is desired to reduce costs and simplify operation.

The authors have proposed an ultrasonic multi-view plane-wave-imaging (PWI) method for nozzle-to-vessel weld inspection from the nozzle side. With half-skip and full-skip PWI, the images are formed using ultrasonic signals whose ray paths include backwall reflections. Then besides signals directly scattered from flaws, the specular reflection from cracks can be captured and imaged. Experimental results show that nozzle sidewalls can be clearly identified as vertical cracks in the half-skip image to help locate not only the position of flaws in the weld geometry, but also the position of the probe around the nozzle. Consequently, a simple encoder-free and nozzle-side inspection was realized to get rid of the beam skewing and reduce mechanism complexity.

However, the detection of transverse planar defects, such as transverse cracks and lack of inter-run fusion, remains a challenge for the outside nozzle inspection because the specular echoes from these defects can never be received even through the backwall reflections. Therefore, more ultrasonic path skips are considered in this paper, especially the paths involving reflections at the vertical sidewall. Thus, utilizing the path consisting of 5 successive skips on the nozzle backwall and sidewall, the transverse defects can be detected and imaged.

Simulation was performed using forward CIVA UT software to validate proposed method. Two planar rectangular defects of length 4mm was embedded in a set-through nozzle weld. Their orientation angles were 25° and 35° , respectively, with relative to the vertical sidewall. Results show that both these defects can be imaged and characterized along with position and sizing accuracy within 1 mm and angle deviation below 3° . Although many nonphysical indications were observed in the image, the origins of these artifacts were analyzed by explicitly simulate each ray path and results show that artifacts in one image mode are mainly induced by physical indications detected in the other modes. Experiment was also performed on a reference steel block containing a  35° Electrical Discharge Machined notch, mimicking a transverse crack in the nozzle weld geometry. Results were similar to those of simulation, validating the proposed method.

Presenting Author: Xintao Xu Zhejiang University

Presenting Author Biography: Xintao Xu is currently working toward the Ph.D. degree at Zhejiang University.
His interests are in ultrasonic phased array imaging and modelling.

Authors:

Xintao Xu Zhejiang University
Haoran Jin Zhejiang University
Zhenyang Yu Zhejiang University
Keji Yang Zhejiang University