Resistance of Aluminide Coatings on Austenitic Stainless Steel in a Nitriding Atmosphere

A new slurry cementation method was used to produce silicide-aluminide protective coatings on austenitic stainless steel 1.4541. The slurry cementation processes were carried out at temperatures of 800 and 1000 °C for 2 h with and without an additional oxidation process at a temperature of 1000 °C for 5 min. The microstructure and thickness of the coatings were studied by scanning electron microscopy (SEM). The intention was to produce coatings that would increase the heat resistance of the steel in a nitriding atmosphere. For this reason, the produced coatings were subjected to gas nitriding at a temperature of 550–570 °C in an atmosphere containing from 40 to 60% of ammonia. The nitriding was carried out using four time steps: 16, 51, 124, and 200 h, and microstructural observations using SEM were performed after each step. Analysis of the chemical composition of the aluminide coatings and reference sample was performed using wavelength (WDS) and energy (EDS) dispersive X-ray microanalysis, and phase analysis was carried out using X-ray diffraction (XRD). The resistance of the aluminide coatings in the nitriding atmosphere was found to depend strongly on the phase composition of the coating. The greatest increase in resistance to gas corrosion under nitriding atmosphere conditions was achieved using a manufacturing temperature of 1000 °C.

Thermally Sprayed Nickel-Based Repair Coatings for High-Pressure Turbine Blades: Controlling Void Formation during a Combined Brazing and Aluminizing Process

Turbine blades must withstand severe loading conditions and damage can occur during operation due to heat, pressure, foreign objects and hot gas corrosion, despite the protective coatings applied onto the turbine blades. Instead of replacing the damaged components, maintenance, repair and overhaul are key to extend the total service life. Besides welding, the repair of turbine blades by brazing is an established repair process in the industry and involves many individual steps that often require a high degree of manual work. In the present study, a hybrid joining and coating technology was developed to shorten the state-of-the-art process chain for repairing turbine blades. With this approach, a repair coating, which consists of a filler metal, a hot gas corrosion protective layer and an aluminum top layer, is applied by atmospheric plasma spraying. The coated turbine blade then undergoes a heat-treatment so that a brazing and aluminizing process is carried out simultaneously. Due to diffusion and segregation processes, pores can occur in the heat-treated coating. In the present study, a full factorial design of experiment was performed to reduce the pores in the coating. The microstructure of the repair coating was investigated by optical- and scanning electron microscopy (SEM), and the impact of the process parameters on the resulting microstructure is discussed.

REPAIR OF NOZZLE BLADES MADE OF HEAT-RESISTANT NICKEL ALLOY ZhS6U

An overview of traditional methods for cleaning the surface of gas turbine engine (GTE) blades from products of gas corrosion and spent coating, methods for restoring the structure and properties of the material of blades using hot isostatic pressing and heat treatment, as well as methods for applying coatings on the inner and outer surfaces of the blades is presented. The main disadvantages of these methods are described, taking into account which the state-of-the-art technology for repairing gas-turbine engine nozzle blades made of ZhS6U alloy has been developed in FSUE «VIAM», which ensures an increase in their resource and a reduction in repair costs.

Review on Corrosion Inhibitors for Oil and Gas Corrosion Issues

The pipeline system in the oil and gas industry is the heart for transportation of crude and refined petroleum. Nevertheless, continuous exposure of the pipeline surfaces to impurities and sources of corrosion such as sulfur and chromate is totally unavoidable. Vast employment of commercial corrosion inhibitors to minimize the corrosion is being restrained due to toxicity towards the environment. The emergence of “green” chemistry has led to the use of plant extracts and fruit wastes which have proven to be good corrosion inhibitors. This paper aims to provide insight into carrying out further investigation under this research theme for accurate inhibition efficiency measurement.

THE EFFICIENCY OF CRUDE CORROSION INHIBITOR AND GAS CORROSION INHIBITOR BY USING CARBON STEEL 1018 WITH POLARIZATION METHOD

Carbon Steel 1018 is a low carbon steel having a carbon content (C) of 0.14-0.20% (<0.30% C). Low carbon steel is commercially known as mild steel. Corrosion is one way to prevent corrosion caused by the environment. Corrosion inhibitor are taken between the Crude Corrosion Inhibitor and Gas Corrosion inhibitor on Carbon Steel 1018 using the polarization method. Corrosion inhibitors work by making passive layers in the form of thin films or films on the surface of the material used as a barrier between metals and corrosive media. The analysis method used is polarization. Inhibition Efficiency Results obtained for Gas Corrosion Inhibitors (1A) at 10 ppm 96.86%, 20 ppm 59.74%, 30 ppm 74.48%. The Crude Corrosion Inhibitor (2A) results obtained inhibition efficiency for 10 ppm 99.57%, 20 ppm 77.69%, and 30 ppm 12.63%. The optimum value for the Gas Corrosion Inhibitor and Crude Corrosion Inhibitor is at 10 ppm at 96.86% and 99.57%. Keywords: carbon steel,crude corrosion inhibitor, corrosion , gas corrosion inhibitor, inhibitor

Experimental and numerical analyses of an U-bend tube made of an output inter-heater tube after exploitation

One of the important tasks of evaluating the integrity of mechanical process elements and structures is to determine the local mechanical properties. In this paper, experimental and numerical analyses of the mechanical behavior of an output inter-heater tube, made of 12H1MF heat-resistant steel, was performed after 200,000 h of exploitation. During exploitation, the tube was exposed to various mechanisms of damage including gas corrosion. The tube was cut from a pipe system during reparations of a thermal power plant, and then cold-deformed by bending to obtain a U-bend tube, which was then used in the experiment. For this purpose, a specimen holder made of structural steel S235 was specifically designed to test such a sample. The U-bend tube was then exposed to the external compressive load during the experiment. Experimental research was based on the application of the 3D digital image correlation (DIC), while a finite element method (FEM) was applied in numerical simulation performed by using the Abaqus software package. The 3D DIC is an optical and contactless experimental method that allows measurements of displacement fields and deformations of geometrically complex structures. The Aramis system was used for the experimental analysis as well as for verification of the numerical model. During the experiment, the von Mises strain field was measured at the top of the U-bend tube, in the tightening zone, as it represents a critical place for crack initiation and propagation during the work of an inter-heater. Based on the obtained results and a comparative analysis of experimental and numerical values of the von Mises strain field at the U-bend tube, deviation of the model predictions of about 18 % was determined. The FEM predicted smaller values of the von Mises strain field compared to the DIC method. This is the result of an incomplete geometry applied in the model due to deformation that occurred in the bend zone of the U-bend tube, loss of material and the tube surface damage due to the influence of gas corrosion during 200,000 h of exploitation. Experimental analysis has confirmed that the U-bend tube, after 200,000 h of exploitation, can remain in service even if it is damaged due to the effect of gas corrosion.