Seiichi Hamada

Selecting Suitable Probes Distances for Sizing Deep Surface Cracks Using the DCPD Technique

In this study, the way to enhance the sensitivity of evaluating deep surface cracks by DCPD technique using four probes is considered. The potential drops across two-dimensional cracks having different depths are analyzed by the three-dimensional finite-element method. The effect of the distance between current input and output probes and the distance between measuring probes on the change in potential drops are analyzed for a wide range of crack depths. By extending the distance between current input and output probes, the change in potential drop with the change in the depth of deeper crack becomes large. But the voltage of potential drop becomes small to measure. Finally, the way to select the appropriate distances between the probes for the measuring sensor is shown from the viewpoints of sensitivity and the required current.

Accuracy Comparison of the Electrical Potential Drop Technique and Ultrasonic Testing for the Pipe Wall Thinning in the Thermal Power Plant

The electrical potential drop technique is one of the promising methods for monitoring the pipe wall thinning. In the previous paper [1], it was reported that this technique had a good performance equal to the ultrasonic testing in the preliminary test and that it had a long-term durability under a severe condition on the real pipes in operating thermal power plants. This time one of these pipes was replaced because its thickness approached the threshold. The removed pipe was cut in many pieces and its thickness was measured with calipers at several locations corresponding to where the electrical potential drop technique was applied. This result was compared with the thickness resulted from this technique and the conventional ultrasonic testing that were conducted just before the pipe removal. This comparison led to the conclusion that the accuracy in the electrical potential drop technique was almost equivalent to that in the ultrasonic testing even in the real pipe under a severe condition. In this paper, the accuracy in the electrical potential drop technique is mainly discussed.Copyright

Theoretical and Experimental Investigation of Pipe Wall Thinning Detection Using Guided Waves

A method to investigate pipe wall thinning using guided waves has been developed for pipes in thermal power generation facilities. In this paper, the reflection coefficient and the transmission coefficient are derived for the torsional waves which propagate along a pipe and a simplified method to predict the waveform is proposed. The predictions of the waveforms by the FEM and a simplified method based on the reflection of torsional waves are also examined by comparing with experimental data.Copyright

Application of Potential Drop Technique to the Inspection of Welded Boiler Pressure Parts

In this paper, a practical method using the electrical potential drop technique was discussed to evaluate the creep damage accumulated in the welded power piping such as main steam pipe and hot reheat pipe. Round robin experimental measurements conducted by the authors et al. as academic activities in the Japanese Society for Non-destructive Inspection showed that the potential drop technique is effective for the application to the inspection of welded boiler pressure parts. The authors have conducted additional experimental and numerical studies for verification focusing on the application of the pulsed direct current potential drop technique. The authors have proposed technical requirements on the potential drop technique for the application to the inspection of welded power piping to be implemented in JSME Codes for Thermal Power Generation Facilities (2003 Edition) as a non-mandatory appendix JA. And the practical on-line measurement in the high temperature and high pressure burst test using the repair-welded power piping has been conducted. In this burst test, Tokyo Electric Power Company has tried to monitor the creep damage accumulated in the seam-welded area using the commercialized tool based on pulsed direct current potential drop technique.Copyright

A method of crack detection in the turbine blade using digital holographic microscopy (DHM)

The authors proposed an NDE method of detecting the crack developed in the turbine blade by means of digital holographic microscopy (DHM). UT procedures sometimes have limitations in particular cases of in-service-inspections such as the detection and sizing of a creep crack developed in the air-cooled casting blade of the combined cycle gas turbine. The local displacement at the blade surface near the crack during a mechanical loading is different from that of a non-cracked blade. This small different can be detected by DHM. The authors discussed whether this difference affected by the mechanical load between the cracked blade and the non-cracked is detectable by means of DHM or not. In this paper, the authors verified the practical validity of the proposed NDE method using the finite element analyses.Copyright

Outline of the JSME Mandatory Rules for Thermal Power Generation Facilities as the Harmonized Code in the Regulatory Requirements

The Japan Society of Mechanical Engineers (JSME) issued the latest edition of Rules on Thermal Power Generation Facilities (JSME S TA1, TA2-2008) and the Mandatory Rules (JSME S TA0-2008) to satisfy the Japanese Electric Utility Industry Law and the Ministerial Ordinance (MO) No.51 of Ministry of Economy, Trade and Industry (METI). This Mandatory Rules were developed and described in form corresponding to the text of the regulatory Interpretations of MO No.51. Japan Electric Standards Committee (JESC) reviewed and evaluated these JSME Rules and proposed METI to accept the JSME Mandatory Rules as the harmonized code in MO No.51 of METI. These JSME Rules are basically equivalent to the ASME B & PV and Piping codes. In this paper, differences between JSME Rules and the ASME Rules were described to be helpful for the ASME Code users.Copyright

General Rule of Method for Measurement of Thickness and Crack Size by Electric Potential Drop Technique: Outline of the NDIS3426:2008

The Japanese Society for Non-Destructive Inspection (JSNDI) published general rule of method for measurement of thickness and crack size by Electric Potential Drop Technique as the Standard of JSNDI (NDIS3426) in January, 2008. NDIS3426 was established based on the researches for many years including the round robin tests conducted as the academic activities in JSNDI, and the previous technical guideline and standard ASTM E-647-05 ANNEX A6 and BS ISO 12108:2002 established for the measurement of fatigue crack growth in specimens. In this paper, the outline and the background of NDIS3426 was described. The electric potential drop technique is one of the promising methods to monitor or measure the thickness and crack size for the practical use in many industries. For the inspection of the surface deep fatigue crack in the steam turbine casing, the advanced crack depth indicator based on the potential drop technique has been applied. For the monitoring the creep damage accumulated in the seam-welded power piping, the commercialized tool based on the pulsed direct current potential drop technique has been used. For the pipe wall thinning measurement in the operating thermal power plant, the pulsed direct current potential drop technique was applied. This paper shows the present condition of the practical use and the future prospect of the potential drop technique.Copyright

An Evaluation System of Tube Wall Thickness of Feed Water Heater Base on the Advanced NDE Technique

The inspection of the tubes of feed water heaters on the wall thickness is generally conducted using the ultrasonic pulse technique. According to the past method, the wall thickness at each measured point is evaluated in comparison with the minimum required wall thickness of the tube, namely it is based on the general metal loss evaluation criteria. However, these tubes often show the local metal loss due to erosion and corrosion. Evaluation techniques and acceptance criteria regarding the locally thinned tubes require many wall thickness data around the local metal loss locations. However, it is inefficient to perform this evaluation work with human power because of the required huge measured data. With recent improvement of the inspection technique, technology enabled faster, larger amount, and more accurate electronic digital data acquisition of tube wall thickness. The authors have developed the systematized evaluation methodology that can transact data acquisition and evaluation simultaneously. This paper describes the logic of evaluation methods and examined algorithms to make them systematized.Copyright

Application of the Electrical Potential Drop Technique to the Pipe Wall Thinning Monitoring in Thermal Power Plants

The electrical potential drop technique is one of the promising methods for monitoring the pipe wall thinning. In order to verify this method, preliminary thickness measurements were conducted for uniform and local thinning created on plate specimens. The result showed the electrical potential drop technique had a good performance equal to the ultrasonic testing method. The success in the preliminary tests allowed this technique to be applied to some pipes in thermal power plants in order to monitor the wall thinning and this on-line monitoring has continued for two to three years. It was confirmed that this technique was valid in terms of a long-term durability. Following these results, technical requirements on the potential drop technique were proposed to the JSME (the Japan Society of Mechanical Engineers) Rules on Pipe Wall Thinning Management for Thermal Power Generation Facilities (JSME S TB1-2006) and stipulated in those rules. In this paper, these rules are simply introduced and the on-line monitoring of the pipe wall thinning by means of the electrical potential drop technique is discussed through the results in the plate-specimen-tests and the real-pipe-tests in operating thermal power plants.Copyright

Outline of the JSME Rules on Pipe Wall Thinning Management for Thermal Power Generation Facilities

In response to the pipe wall thinning damage experienced in power plants in 2004, the Japan Society of Mechanical Engineers (JSME) has started activities to develop technical standards on the pipe wall thinning management. The first edition of the JSME rules on pipe wall thinning management for thermal power generation facilities (JSME S TB1-2006 [1]) was issued in March 2006, and its latest edition will be issued in 2007, which describes the technical requirements to meet the JSME performance-based rules for pipe wall thinning management (JSME S CA-1 2005 [2]). Based on 24,774 inspection data obtained at the thermal power plants in Japan, the latest JSME rules will show the specific attention to the need for inspection of piping systems that are susceptible to the wall thinning damage. The JSME rules describe the selection of thickness measurement locations such as downstream of piping configurations that produce turbulence, downstream of orifices, downstream of control valves, and they describe the periodic inspections including the first inspection to be scheduled taking the wall thinning rate data at the equivalent locations into consideration. The JSME rules stipulate some available inspection methods such as ultrasonic scanning, radiographic profile, eddy current and potential drop technique. This paper presents outline of the JSME rules including basic philosophy, technical requirements on the inspection and testing practices and the relation with the regulations in Japan.Copyright