Abstract:
Welding process involves melting and subsequent cooling and the result of this thermal cycle causes residual stress and degradation of mechanical properties in weldments, when welding thicker sections. In thicker section like pressure vessels, boilers which are used in petrochemical, chemical oil & gas industries the existence of residual stress and un desirable mechanical properties are unacceptable as per critically of these structures.
In the present work the effect of welding current when voltage remain constant at different parameter and after that Mechanical and microstructural properties of Chromium-Molybdenum alloy steel of ASTM A 387 Gr- 11 alloy steel is determined, which is commonly used in boilers, pressure vessels, heat exchangers, turbine parts etc. The regions in the weldment like base metal, HAZ and weld metal were studied, through the results obtained from the tensile test, Hardness measurement, Charpy-V-Notch impact test, Microstructural characterization using SEM and optical microscope and chemical analysis using E-DAX. It is concluded that the degradation of mechanical properties of steel is due to the changes .that occurred in the microsture.
Material degradation at high temperature is a serious problem in power plants, which encounter severe corrosion problems resulting in the substantial loss. The problems become more prominent as the power plants getting older. The boiler tubes used for super heaters and reheaters in the steam generating systems are subjected to corrosion, resulting in tube wall thinning and premature failure. Hot corrosion has been identified as a serious problem in high temperature applications such as boilers, gas turbines, diesel engines, coal gasification plants and chemical plants.
The present has been performed to evaluate the hot corrosion behavior of chromium-molybdenum alloy steel when exposed to high temperature oxidation in air environment, under isothermal conditions at a temperature of 900°C, in actual degrading conditions prevailing in a coal fired boiler of a thermal plant. The work is focused on Base metal and weld metal. Isothermal treatment resulted in parabolic oxidation kinetics and thus resulted in weight gain.
