Evaluation of semi-ellipsoidal wall thinning on back surface of plate by direct-current potential difference method

2015 ◽  
Vol 6 (6) ◽  
pp. 714-724 ◽  
Author(s):  
Naoya Tada ◽  
Manabu Nohara
Keyword(s):  
Electric Field ◽  
Direct Current ◽  
Difference Method ◽  
Front Surface ◽  
Potential Difference ◽  
Back Surface ◽  
Content Type ◽  
Wall Thinning ◽  
Current Potential ◽  
Local Wall Thinning

Purpose – Local wall thinning is one of serious problems in aged power generating plants. As the thinning grows inside the pipes, it is difficult to detect and evaluate it from the outer surface of pipe. The purpose of this paper is to evaluate the method of semi-ellipsoidal wall thinning geometry on the back surface of flat plate by direct-current potential difference method (DC-PDM) was proposed as a preliminary research for the pipe wall thinning evaluation. The evaluation was performed for the potential difference numerically obtained by finite element method and the results were discussed. Design/methodology/approach – A number of electric field analyses are necessary to evaluate the geometry of local wall thinning. In this study, defect-current modification method (DCMM), which is very fast analysis method based on the formulated solution for the similar thinning geometry, was used. The DCMM enabled the repeated electric field analyses necessary for the evaluation. Findings – The potential difference on the front surface of plate was higher than the other part because of the electric current disturbance by a wall thinning on the back surface. In addition, the distribution depended on the geometry of the wall thinning. In this study, the shape of the thinning was assumed to be ellipsoid, and the width, depth, and length of the thinning were successfully evaluated based on the potential difference distribution on the front surface. Originality/value – Evaluation of local wall thinning geometry was carried out by repeated analyses using DCMM, and the results were successful. This fact suggests that the evaluation of local wall thinning is possible by DC-PDM. The proposed method is going to be extended to the local wall thinning on the inner surface of pipe by geometrical conversion.

Electric Field Analysis of Simultaneous Evaluation of Crack on an Inner Pipe Surface and Pipe Wall Thickness Using Direct-Current Potential Difference Method of Multiple-Probe Type

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Naoya Tada ◽  
Makoto Uchida
Keyword(s):  
Electric Field ◽  
Wall Thickness ◽  
Direct Current ◽  
Difference Method ◽  
Pipe Wall ◽  
Potential Difference ◽  
Pipe Wall Thickness ◽  
Simultaneous Evaluation ◽  
Inner Surface ◽  
Current Potential

The direct-current potential difference method (DC-PDM) is a promising nondestructive technique for evaluating cracks in the conductors on the basis of change in current paths or the potential difference due to cracks. In a previous study, the authors proposed a method for the simultaneous evaluation of the location and size of a semi-elliptical crack on the back surface of a plate and the plate thickness. Its theoretical validity and practical utility were shown by numerical analyses and experiments. This study extends the method to the simultaneous evaluation of a crack on the inner surface of a pipe and the pipe wall thickness. The related electric field analyses are performed using the finite element method. The results show that the location, length, and depth of a semi-elliptical crack on the inner surface of the pipe and the pipe wall thickness can be evaluated based on the distribution of the potential difference measured on the outer surface of the pipe. This extension will prove useful for various practical cases, which are often seen in the piping of power-generating and petrochemical plants.

Finite Element Analysis for the Evaluation of Cracks at a Pipe-Flange Welded Part by the Direct-Current Potential Difference Method

2015 ◽  
Author(s):  
Naoya Tada ◽  
Masaki Kosaka
Keyword(s):  
Finite Element ◽  
Direct Current ◽  
Difference Method ◽  
Evaluation Method ◽  
Fatigue Cracking ◽  
Potential Difference ◽  
Piping System ◽  
Element Analysis ◽  
Non Destructive ◽  
Current Potential

The use of a flange joint is a popular method to close the end of pipes or connect pipes in manufacturing industries. As the pipes are often subjected to vibrations and cyclic bending, fatigue cracking may occur at the welded part between the pipe and flange. It is therefore important to detect and monitor the cracking in this part to ensure safety of the whole piping system. The direct-current potential difference method (DC-PDM) is known as a suitable non-destructive technique to monitor the initiation and growth of cracks and it has been applied to cracks and wall thinning on the inner surface of pipes. In this study, finite element analyses were carried out to clarify the relationship between the size and location of cracks at the pipe-flange welded part and the potential difference. An evaluation method of circumferential crack length angle by DC-PDM was proposed.

Detection of Stress Corrosion Cracking by Direct-Current Potential Difference Method

2011 ◽  
Author(s):  
Naoya Tada ◽  
Makoto Uchida ◽  
Hiroki Maeda ◽  
Atsushi Hozuki
Keyword(s):  
Stress Corrosion ◽  
Direct Current ◽  
Stress Corrosion Cracking ◽  
Difference Method ◽  
Corrosion Cracking ◽  
Potential Difference ◽  
Measurement Results ◽  
Detection Of Stress ◽  
Metal Weld ◽  
Current Potential

Stress corrosion cracking (SCC) is one of serious damages occurred in power generating plants, petrochemical plants, and gas pipelines. However, it is not easy to detect and evaluate SCCs because their shapes are complex and they are usually initiated in the weldment composed of base metal, weld metal, and heat-affected zone. In this study, the direct-current potential difference method (DC-PDM) was applied to SCCs artificially introduced in plate specimens and the applicability of DC-PDM to their detection was discussed. It was found from the measurement results that the potential differences near SCC were higher than those away from SCC. This fact suggests that SCC is detectable by DC-PDM.

Three-Dimensional Identification of Semi-Elliptical Crack on the Back Surface by Means of Direct-Current Electrical Potential Difference Method With Multiple-Probe Sensor (PVP2006-ICPVT-11-93359)

2008 ◽  
Vol 131 (2) ◽  
Author(s):  
Naoya Tada ◽  
Akira Funakoshi
Keyword(s):  
Direct Current ◽  
Difference Method ◽  
Electrical Potential ◽  
Three Dimensional ◽  
Elliptical Crack ◽  
Potential Difference ◽  
Back Surface ◽  
Electrical Potential Difference ◽  
Multiple Probe ◽  
Probe Sensor

Cracks are popular defects initiated in structural components and their accurate evaluation is very important to assure the reliability of various plants. The direct-current electrical potential difference method is known as one of the most effective methods for the evaluation of the cracks. In this paper, a method of three-dimensional identification of a semi-elliptical crack existing on the back surface of a conductive plate by the direct-current electrical potential difference method with a multiple-probe sensor is proposed. The geometrical condition of the crack was specified by six parameters, the surface and inward angles of the crack plane, θsur and θin, the length and depth of the crack, c and a, and the two-dimensional location of the crack center, (yc,zc), on the back surface. The identification was carried out based on the distribution of electrical potential difference on the surface of the plate measured with a sensor composed of grid-arranged multiple probes called the “multiple-probe sensor.” As an approximate cracked body and a quick analysis method were used, a number of repeated electrical potential field analyses necessary for the identification of the crack became possible within a practical time. The validity of the method was numerically confirmed by carrying out the identification based on the result of the finite element analysis. The proposed method could be extended to the online monitoring of a semi-elliptical crack initiated on the inner surface of tubular components by means of the multiple-probe sensor placed on the outer surface.

Sign in / Sign up

Export Citation Format

Share Document