Modification of Repair Welding on Control Valves and Flanges of Sure Gas

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Mohammad, Nasr Esfahani | 2010

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Type of Document: M.Sc. Thesis
Language: Farsi
Document No: 40717 (07)
University: Sharif University of Technology
Department: Materials Science and Engineering
Advisor(s): Kokabi, Amir Hossein
Abstract:
In this research, for optimization of repair welding of control valve and flange that use in East Oil& Gas Company, effect of chemical composition, microstructure, hardness and stress relive on sulfide stress cracking (SSC) investigated with select of four electrodes. All welds were prepared by shielded metal arc welding (SMAW) and investigated with optical microscope, hardness test, tensile test and SSC test. The results showed that increase of nickel content in the range of 0.032–1.58 wt. % in weld metals, decrease of acicular ferrite and increase of side plate ferrite, grain boundary ferrite and M/A micro constituent in microstructure. Ni3S2 decrease SSC resistance and (FeCu).S increase SSC resistance. SSC resistance of steel No.2 is more than steel No.1 and SSC resistance of steel No.1 is more than steel No.3. Stress relives after repair welding increases SSC resistance.
Keywords:
Sour Gas ; Stress Relieving ; Acicular Ferrite ; Nickel ; Sulfide Stress Cracking (SSC)