The current work presents a finite element analysis (FEA) based investigation of the structural steel pipe with internal corrosion defects. A total of 27 different geometrical conditions for internal corrosion defect were considered using 3 different internal pressures of 2.2 MPa, 4.5 MPa, and 6 MPa. The validation of the FEA model was carried out using the analytical solution for failure pressure using radial and hoop stresses. The failure pressure of the uncorroded pipe was 11.5 MPa. In contrast, for pipe with internal corrosion defect having the largest defect depth (1.7 mm), largest length (454 mm), and sharpest geometry (width of 26 mm), the failure pressure from FEA was 6 MPa. The remaining strength at this boundary condition was 0.521. The radial stress influences the strain in wall thickness which was 8.8 mm and much less as compared to other dimensions of pipeline which diminishes the material's ability to resist the failure pressure. The Von-Mises stress accumulation inside the interface increases the stress intensity (K) distribution at the vicinity of the internal corrosion defect geometry vis-à-vis lowers the K-distribution just outside of the internal corrosion defect. The largest factor of safety (FOS) of 2.11 was obtained at threshold boundary conditions considering fatigue limit as the optimum stress. It is then suggested that the FOS for the "break-before-leak" leak model can be anywhere between 2.11 to 1.45 and hence the pipeline cannot burst into rapture.

Inconel 825 is high nickel-chromium-based superalloy which retains its mechanical properties and exhibits good corrosion and oxidation resistance at elevated temperature. Inconel 825 is extensively used for making aircraft engine parts like combustor casing and turbine blades in aero space industry. This research proposed the Response Surface Methodology with GRA to optimize multiple responses during Wire-cut EDM of Inconel 825. At optimum combination of input parameters i.e. A4B1C1D5E4F2, increase in MRR from 36.13 mm2/min to 41.822 mm2/min, decrease in SR from 2.842μm to 2.445μm and decrease in WWR from 0.01832 to 0.01758 was obtained. Experimental results showed that pulse-on time, wire feed, pulse-off time, and peak current significantly affected the MRR, and surface integrity of specimen and electrode with the formation of craters, pockmarks, debris, micro cracks, and recast layer. The optimal parametric combination obtained from the present study will be advantageous for working on high strength; high thermal conductivity and low melting point materials like nickel alloys.

WEDM has evolved as a well admired technique for machining of difficult to cut materials such as superalloys. WEDM produces intricate shape and profiles of superalloys by thermoelectric erosion process. But as the process is carried out at very high temperature, the formation of heat affected zone, microcracks, recast layer, porosity etc. resulted in decreased surface integrity of machined specimen and becomes a big problem in WEDM. Discharge energy is the most influencing param-eters that affect the surface integrity of WEDmed samples. In this study, Inconel 825, widely used in aerospace industry for making of combustor casing and turbine blades, was machined with WEDM under different discharge energy. The surface topography of the WEDMed specimen was carried cut by using SEM, XRD and EDX techniques. It was observed from the SEM micrograph that the machined surface includes cracks, pockmarks, craters, and pulled out material. The density and sice of craters increase with increase in discharge energy. Surface crack density of 0.0138 μm/μm2 and recast layer thickness of 34.62μm was obtained for the machined sample at high value of discharge energy while at low value surface crack density of 0.0016 μm/μm2 and recast layer thickness of 20.99μm was observed. EDX and XRD analysis of the specimen showed that an ap-preciable amount of elements viz. Fe (Ferrous), Cr (Chromium), Cu (Copper), Ni (Nickel) are mi-grated to the surface of the workpiece at high value of pulse on time.