Metallographic tests, micro-hardness tests, mechanics performance tests and Energy Dispersion Spectrum (EDS) were conducted for a 2.25Cr-1Mo main steam pipe weldment served for more than 32 years. Microstructural evolution of the 2.25Cr-1Mo base metal and weld metal was investigated. Degradation in micro-hardness and tensile properties were also studied. In addition, the tensile properties of subzones in the ex-service weldment were characterized by using miniature specimens. The results show that obvious microstructural changes including carbide coarsening, increasing inter lamella spacing and grain boundary precipitates occurred after long-term service. Degradation in micro-hardness is not obvious. However, the effects of long term service on tensile deformation behavior, ultimate tensile strength and yield stress are remarkable. Based on the yield stress of micro-specimens, the order of different subzones is: WM>HAZ>BM, which is consistent with the order of different subzones based on micro-hardness. However, the ultimate tensile strength and fracture strain of HAZ are lower than BM.

In the design of a downhole isolation tool for multi-stage fracturing in the oil and gas industry, a setting component, called slip, was used to set the tool in the casing prior to the hydraulic fracturing operation. The material of the slip is made of gray cast iron with surface hardening requirement. This study investigated the performance of slips treated by induction hardening versus flame hardening. The slip treated by induction hardening produced low hardness and insufficient affected layer. On the other hand, flame hardening generated satisfactory results of case hardening layer by 0.762 mm (0.030 in.) thickness with 50 HRC minimum hardness. The Type E graphite in the raw material was transformed to Type A in the flame hardening process, which is favored in the case hardened layer. The effect of different treatment processes on the affected layer and their microstructural response in gray cast iron was discussed in this study. The isolation tool using the slip treated by flame hardening, together with other proven components, showed successful performance of 82.7 MPa (12 ksi) pressure holding at 177 °C (350 °F) for high pressure and high temperature downhole applications.