Effects of dry turning parameters of Incoloy 800H superalloy using Taguchi-based Grey relational analysis and modeling by response surface methodology

Incoloy 800H is an austenitic Fe-Ni-Cr based superalloy and used in many applications due to their high corrosion resistance and creep-strength. However, this alloy is difficult to machine or cut material because of their eminent characteristics such as rapid-work hardening, lesser thermal conductivity and easy to tool-material attraction. Hence, the necessary experimental investigation is required to study and optimize the turning parameters of this alloy. This work presents the investigation of turning parameter effects on the Incoloy 800H superalloy with cryogenically treated cutting tool. The dry turning experiments were conducted based on Taguchi L9 Orthogonal array (OA) with the input parameters of cutting speed, feed rate and depth of cut. The outputs such as material removal rate, surface roughness, cutting force and tool-tip temperature were considered as the responses. The measured output responses were optimized and modeled using Taguchi-based Grey relational analysis (GRA) and response surface methodology (RSM), respectively. The tool flank wear and tool life were examined on coated insert with cryogenically treated, coated insert (without cryogenic treatment) and uncoated insert for comparison. The results revealed that greater amount of tool-wear reduction was observed in the case of coated tool with-cryogenically treated about 47.88%, coated tool without-cryogenically treated about 27.51% when compared with an uncoated tool. Besides, analysis of variance (ANOVA) was performed to find the most significant parameter over the obtained responses. The obtained mathematical model through RSM was agreed with the experimental result. Further, the machined surface topography was examined using White Light Interferometer (WLI).

Failure Analysis of a Flare Tip Used in Offshore Production Platform in Qatar

An immature failure of a gas flare tip used in Qatar oil and gas offshore industry was investigated throughout this study. The design lifetime of the flare was fifteen years; however, it manifested immature failure resulting in a reduction of its lifetime to ten years. The flare is composed of different parts where the upper flare body and wind deflector showed failure while other components were still healthy. The material used for the aforementioned failed parts was Incoloy 800H, which is a highly corrosion and high-temperature resistant steel alloy. The material was rolled up and welded together with different welding joints. The root cause of failure was identified by using chemical analysis and microstructural and mechanical characterizations. For the mechanical characterization, an optical microscope (OM) and scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS) analyses were used for the specimen extracted from the failed part in order to ensure that the material mentioned by the manufacturer demonstrated the same metallurgical properties. For the mechanical characterization, two sets of specimens were used, one close to the failure region and the other far from the failure area. The chemical analysis revealed that the material was truthfully Incoloy 800H. The mechanical examination results showed a significant reduction of mechanical properties, i.e., the ultimate tensile strength (UTS) and microhardness dropped by 44% and 41% for samples close and far from the failure regions, respectively. Careful examination of the failed parts indicated that failure mostly took place in the vicinity of the welds, in particular near the joints. Improper joint designs, as well as a number of joints being designed in tiny areas, worsened the harmful effect of the heat-affected zone (HAZ), resulting in crack nucleation in the HAZ regions. The effect of welding in a combination of harsh service conditions of flare caused further crack extension where they merged, resulting in final immature failure.