Hot Corrosion of Weldments

Hot corrosion of the weldment is the result of the reaction between oxidation and sulfidation, which affects welded joints exposed to combustion gases containing sulfate coal ash at high temperature. It is also demonstrated that welding processes, weld consumables, temperature of exposure, and mixture of salt environment are important factors in hot corrosion of the weldment

Polyphenol-rich pomegranate fruit extract (POMx) suppresses PMACI-induced expression of pro-inflammatory cytokines by inhibiting the activation of MAP Kinases and NF-κB in human KU812 cells

<p>Abstract</p> <p>Background</p> <p>Mast cells and basophils are multifunctional effector cells and contain plentiful secretary granules in their cytoplasm. These cell types are involved in several inflammatory and immune events and are known to produce an array of mediators including a broad spectrum of cytokines. Pomegranate fruit is rich in anthocyanins and hydrolysable tannins; a group of polyphenolic compounds shown to be potent antioxidant with anti-inflammatory activity. However, no studies have been undertaken to investigate whether a polyphenol-rich pomegranate fruit extract (POMx) inhibits the inflammatory activity of activated human mast cells and basophils. The aim of this study was to examine whether POMx modulates inflammatory reactions using human basophilic cell line KU812.</p> <p>Methods</p> <p>KU812 cells were stimulated with phorbol-12-myristate 13-acetate plus calcium inophore A23187 (PMACI). The inhibitory effect of POMx on pro-inflammatory cytokine gene expression and production by stimulated KU812 cells was measured by quantitative RT-PCR, and cytokine-specific ELISA assays, respectively. Western blotting was used to analyze the effect of POMx on the activation of mitogen-activated protein kinases (MAPKs), and the nuclear factor (NF)-κB in PMACI stimulated KU812 cells. Effect on the activity of NF-κB was determined using Luciferase reporter assay. Significance of differences from control values were analyzed by means of standard statistical methods.</p> <p>Results</p> <p>POMx significantly decreased PMACI stimulated inflammatory gene expression and production of interleukin (IL)-6 and IL-8 in KU812 cells. The inhibitory effect of POMx on the pro-inflammatory cytokines was MAPK subgroups c-jun N-terminal kinase (JNK)- and extracellular-regulated kinase (ERK) dependent. In addition, POMx suppressed the NF-κB activation induced by PMACI by inhibiting IκB-degradation in human basophil cells. POMx also suppressed the powerful induction of NF-κB promoter-mediated luciferase activity in transiently transfected KU812 cells.</p> <p>Conclusion</p> <p>These novel pharmacological actions of POMx provide new suggestion that POMx or POMx-derived compounds may be of therapeutic use for the treatment of inflammatory diseases by suppressing mast cells/basophils activation.</p

Improvement in hot corrosion resistance of dissimilar alloy 825 and AISI 321 CO2-laser weldment by HVOF coating in aggressive salt environment at 900°C

This study investigated the hot corrosion performance of a dissimilar weldment of Ni-based superalloy and stainless steel joined by CO2-laser welding and improved by high-velocity oxy-fuel (HVOF) coating in a Na2SO4-60wt%V2O5 environment at 900°C. A dissimilar butt joint of AISI 321 and alloy 825 was fabricated by CO2-laser welding with low heat input after obtaining the optimum welding parameters by bead-on-plate trials. The metallurgical and mechanical properties of the laser weldment were evaluated. The tensile test results indicated the occurrence of fracture in the base metal AISI 321 side. The HVOF process was employed to coat Ni-20wt%Cr on the weldment. To evaluate the surface morphology of the corrosion products formed on the uncoated and Ni-20wt%Cr-coated weldments, scanning electron microscopy (SEM) analysis was performed. Energy-dispersive spectroscopy (EDS) was used to determine the different elements present on the surface scales. The existence of oxide phases on the weldments was determined by X-ray diffraction (XRD). The cross sections of the weldments were characterized by SEM with EDS line mapping analysis. The results indicated that the Ni-20wt%Cr-coated weldment exhibited superior hot corrosion resistance due to the development of Cr2O3 and NiCr2O4 protective oxide scales

Micro-segregation Studies on the Continuous Nd: YAG Laser Beam Welded AISI 316L

AbstractThis Experimental research article presents a bead on plate welding of AISI 316L welded with continuous Laser Beam Welding (LBW). An attempt is made to find a process parameter for a full penetration weld bead profile; with less segregation effect. The experiments were carried out in two sets on an AISI 316L austenitic stainless steel plate (200 × 150 × 5mm). In the first set, trial welds were carried out by keeping the laser speed at 400mm/min and in the second set; it was kept at 800mm/min. In both the cases, the laser power was varied from 1000W, 1500W and 2000W. Metallurgical and mechanical characterizations were carried to evaluate the weld beads. Macro and micro structural analysis is carried done to evaluate the bead profile and microstructures. Ferrite content in terms of ferrite number (FN) in the weld zone is evaluated using Fischer Feritscope. Scanning Electron Microscope (SEM)\Energy Dispersive X-ray Spectroscopy (EDS) was used to characterize the weld beads for segregation effect. Vickers micro hardness test was carried out across the cross section of the weld beads to find the hardness distribution. Better result was obtained for the trial bead with parameter 800mm/min and 2000W