Accepted In Conventional ultrasonic non-destructive condition monitoring the testing personnel use his testing experience to interpret defects by analysing the ultrasonic echo. Owing to the coarse material structure, the ultrasonic waves attenuate more and sometimes it gives a false impression of defect and provides unreliable results. The conventional inspection method is too subjective and highly relies on the effectiveness of testing personnel owing to the fact inspection reliability is low. To overcome these limitations a multi-interrogation ultrasonic technique and correlation of several parameters such as attenuation, acoustic velocity and grain size with material features is ...view middle of the document...
Ultrasonic evaluation enables us to determine  elastic modulus and acoustic properties. Single technology can not cover everything. Each condition monitoring techniques have some advantages and some disadvantages. The recommendation is to incorporate two or more technology to ensure reliable results.
The predominant factor in attenuation measurement is the relationship between the ultrasonic wavelength and the grain size [7, 8, 9, and 10]. The relation is as follows:
High attenuation occurs when λ < D,
Where λ = wavelength, D = grain diameter
Low attenuation occurs when λ > D
Also high attenuation is associated with high level of damage and low attenuation to low level of damage. It means if the wavelength of ultrasonic wave if not properly selected then it give a false impression of the presence of defect in material. Particularly if we know the grain size (Using SEM) of material to be tested then we can easily fix the suitable wavelength for testing.
Using the SEM grain size of specimen can be accurately determined. The scanning electron microscopy  is a highly effective and accurate method. It consists of an electron gun producing an electron beam that is collected at a detector after scattering from the molecules of the material to be tested and sent to a cathode ray tube for display.
The main idea is to combine ultrasonic condition monitoring technique with grain size analysis to improve the reliability of fault detection. The ideal aim is to maintain asset availability, reduce maintenance cost and improve safety conditions.
2. Experimental approach
2.1 Material Selection
Mild Steel is the most common form of steel because of relatively low price although it provides material properties that are acceptable for many applications. Mild steel has a relatively low tensile strength but it is cheap and malleable. In P355N the tensile strength is significantly improved by normalizing. Particularly this material is best suited for high pressure applications such as spiral casing of the turbine. The density of material, d = 8.03. 1000 kg/m3
2.2. Chemical Composition of P355N as Determined by OES
Chemical composition of the specimen is determined by OES. For this a cylindrical specimen of diameter 0.01m and length 0.015 m is used.
Table1. Chemical Composition of P355N EN 10028-3-2009 as Determined by OES
Element By max% Element By max%
C 0.18 Cr 0.30
Si 0.50 Cu 0.30
Mn 1.10-1.70 Mo 0.08
P 0.025 Nb 0.05
S 0.015 Ni 0.50
Al 0.020 Ti 0.03
N 0.012 V 0.01
2.3. Sample Preparation
First of all sample of diameter 0.01 m is prepared. Mirror finishing on the side of the specimen is obtained by Clock Finishing Machine. This is necessary to remove scratches over the specimen.
Fig 1. Sample Preparation
2.4. Analysis by Imaging Microscope and Scanning Electron Microscope
The imaging Microscope instrument provides micro structural images of the sample. It is necessary to...