The paper deals with the measurement of residual stresses in P92 welded pipe using the blind hole drilling technique. The post weld heat treatment (PWHT) of a P92 welded pipe was also conducted to study their effect on residual stresses. The P92 pipe weld joints were prepared using gas tungsten arc welding process. The residual stress measurement was carried out using a strain gauge rosette that was associated with the plastic deformation of the material and a stress concentration effect of a multi-point cutting tool. A corrective formulation was developed for calculating the corrected value of residual stresses from the experimentally obtained strain value. The Strain gauge response was estimated experimentally using tensile testing for uniaxial loading while a finite element analysis was performed for biaxial loading. A gas tungsten arc welds joint was prepared for a conventional V-groove and a narrow groove design.
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The tungsten inert gas welded P91 steel welded joints were subjected to the two different type of heat treatments including the postweld direct tempering (PWDT) and re-austenitizing based tempering (PWNT) treatment. The microstructure of weld fusion and heat affected zone (HAZ) were characterized in different heat treatment conditions using optical microscope and scanning electron microscope. For as-welded joint, a great heterogeneity was observed in microstructure and mechanical properties across the weldments. The Charpy toughness of the as-welded joint was measured much lower than the minimum recommended value of 47 J and it was measured 8 ± 5 J. The PWHTs have found a beneficial effect in decreasing the microstructure heterogeneity across the welded joint and improving the mechanical properties. The PWDT resulted in a drastic improvement in the Charpy impact toughness of the welded joint and it was measured 59 ± 5 J which was higher than the minimum required value of 47 J but still inferior than the base metal. The δ ferrite still remained in overlap zone of the weld fusion zone. The PWNT treatment resulted in homogeneous microstructure and hardness variation across the welded joint in transverse direction and Charpy impact toughness (149 ± 6 J) exceeded than that achieved in base metal.
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