Electromagnetic inspection for defect of ferromagnetic tube using rectangular wave with DC bias

2020 ◽  
Vol 64 (1-4) ◽  
pp. 281-288
Author(s):  
Makoto Tohara ◽  
Yuji Gotoh
Keyword(s):  
Power Plants ◽  
Sine Wave ◽  
Steel Tube ◽  
Detection Sensitivity ◽  
Nonlinear Fem ◽  
Steel Tubes ◽  
Inspection Method ◽  
Rectangular Wave ◽  
Dc Bias ◽  
Non Destructive

The ferromagnetic steel tubes are used as heat exchangers in power plants or oil plants. When the usual eddy current testing (ECT) of inner type is used for the defect inspection of these steel tubes, it is difficult to detect defects on the opposite side due to the influence of skin effects. In this research, the non-destructive inspection method using rectangular wave excitation current with DC bias is proposed for detecting of the opposite side defect. It is shown that the detecting of the opposite side defect in the steel tube is possible, and the detection sensitivity using the alternating magnetic field of rectangular wave is higher than that with sine wave. The detailed phenomenon of the inspection method is examined using the 3-D nonlinear FEM (finite element method) taking account of minor loop magnetizing properties using the play model method.

Properties of 20Cr-25Ni-Mo-Nb-N Steel Tubes Exposed in Eddystone Unit No.1 Boiler for 75,000 Hours

2007 ◽  
Author(s):  
Hiroyuki Mimura ◽  
Tetsuo Ishitsuka
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Power Plants ◽  
Charpy Impact ◽  
Steel Tube ◽  
Stainless Steel Tube ◽  
Boiler Tube ◽  
Steel Tubes ◽  
Long Time ◽  
Austenitic Stainless Steel Tube

A 20%Cr-25%Ni-1.5%Mo-Nb-N austenitic stainless steel tube, NF709, has been developed for boiler tube applications. The calculated maximum allowable stress values for NF709 is much higher than those for other austenitic stainless steel tubes. NF709 test tubes were exposed for 75,075 hours in Eddystone Unit No.1 boiler with a steam temperature of 615°C at the superheater outlet. The removed tubes were investigated metallurgically and mechanically. No severe corrosion was observed on the outer surface. No exfoliation of the outer layer of the steam oxidation scale was observed. One percent of Mo was in solid-solution state even after long-time exposure, which is useful for improving the creep strength. Cr23C6, Nb(C,N), NbCrN and TiN were the main precipitates and the σ(Sigma) phase was slightly detected only in the flame side. Charpy impact values at 20°C of NF709 tubes after exposure was over 40 J/cm2, acceptable for boiler tube use. The time to rupture for the exposed NF709 tubes became closer to that for unexposed ones at lower stresses. The above results indicate that NF709 is a promising material for superheaters and reheaters of power plants with advanced steam conditions.

Human reliability in non-destructive inspections of nuclear power plant components: modeling and analysis

2019 ◽  
Vol 7 (2B) ◽  
Author(s):  
Vanderley Vasconcelos ◽  
Wellington Antonio Soares ◽  
Raissa Oliveira Marques ◽  
Silvério Ferreira Silva Jr ◽  
Amanda Laureano Raso
Keyword(s):  
Power Plant ◽  
Nuclear Power Plant ◽  
Human Factors ◽  
Nuclear Power ◽  
Power Plants ◽  
Failure Modes ◽  
Cooling System ◽  
Human Reliability ◽  
Non Destructive ◽  
Plant Components

Non-destructive inspection (NDI) is one of the key elements in ensuring quality of engineering systems and their safe use. This inspection is a very complex task, during which the inspectors have to rely on their sensory, perceptual, cognitive, and motor skills. It requires high vigilance once it is often carried out on large components, over a long period of time, and in hostile environments and restriction of workplace. A successful NDI requires careful planning, choice of appropriate NDI methods and inspection procedures, as well as qualified and trained inspection personnel. A failure of NDI to detect critical defects in safety-related components of nuclear power plants, for instance, may lead to catastrophic consequences for workers, public and environment. Therefore, ensuring that NDI is reliable and capable of detecting all critical defects is of utmost importance. Despite increased use of automation in NDI, human inspectors, and thus human factors, still play an important role in NDI reliability. Human reliability is the probability of humans conducting specific tasks with satisfactory performance. Many techniques are suitable for modeling and analyzing human reliability in NDI of nuclear power plant components, such as FMEA (Failure Modes and Effects Analysis) and THERP (Technique for Human Error Rate Prediction). An example by using qualitative and quantitative assessesments with these two techniques to improve typical NDI of pipe segments of a core cooling system of a nuclear power plant, through acting on human factors issues, is presented.

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