The effectiveness of aminotrimethylidene phosphonic acid (ATMP) as a corrosion inhibitor in association with a bivalent cation like Zn 2+ and nonionic surfactant like polyoxyethylene sorbitan monooleate (Tween 80) were investigated by measuring corrosion losses using electrochemical techniques. The corrosion of 304 stainless steel in the ground water medium was inhibited by complexation of the inhibitor. A combined inhibition effect was achieved by adding both ATMP and Zn 2+ along with Tween 80. The formulation functioned as a mixed type inhibitor. The synergistic effect of the inhibitor compound is calculated. Luminescence spectra, FTIR spectra, XRD, XPS and scanning electron microscopic studies were carried out to understand the mode of corrosion inhibition and also the morphological changes on the metal surface.
The corrosion inhibition of mild steel by means of newly synthesised triazole phosphonates 3-Vanilidene amino 1,2,4-triazole phosphonate (VATP), 3-Anisalidene amino 1,2,4-triazole phosphonate (AATP) and 3-paranitro benzylidene amino 1,2,4-triazole phosphonate (PBATP) was studied along with cetyl trimethyl ammonium bromide (CTAB) in natural aqueous environment using weight loss measurement, potentiodynamic polarisation and ac impedance measurement. Surface characterisation techniques like FT-IR, XRD and EDXA were also carried out to understand the corrosion inhibition mechanism. Addition of molybdate increases the inhibition efficiency of triazole in a synergistic manner. Results from experimental observation have indicated VATP as a better corrosion inhibitor for mild steel in aqueous solution. Additionally the formulation consisting of VATP, sodium molybdate and CTAB offered good corrosion inhibition efficiency.
Stress corrosion cracking (SCC) is a common mode of failure encountered in boiler components especially in austenitic stainless steel tubes at high temperature and in chloride-rich water environment. Recently, a new type of austenitic stainless steels called Super304H stainless steel, containing 3% copper is being adopted for super critical boiler applications. The SCC behavior of this Super 304H stainless steel has not been widely reported in the literature. Many researchers have studied the SCC behavior of steels as per various standards. Among them, the ASTM standard G36 has been widely used for evaluation of SCC behavior of stainless steels. In this present work, the SCC behavior of austenitic Fe-Cr-Mn-Cu-N stainless steel, subjected to chloride environments at varying strain conditions as per ASTM standard G36 has been studied. The environments employed boiling solution of 45 wt.% of MgCl 2 at 155°C, for various strain conditions. The study reveals that the crack width increases with increase in strain level in Super 304H stainless steels.
There are efforts to develop modified P91 steel (9Cr-1Mo-V) consumables to optimize strength and fracture toughness in weldments for similar and dissimilar welding of 9Cr-1Mo (modified P91) for both new construction and replacement of serviced components. Fracture toughness is an important consideration which plays a vital role in determining the performance and life of the materials under the given service conditions. Toughness characterization was done by the Crack Tip Opening Displacement (CTOD) method. Welding results in a variety of non-equilibrium microstructures in the HAZ of 9Cr-lMo-V, modified P91 steel. These variations of microstructures from wrought base material through transformed HAZ to cast weld metal, may give rise to considerable inhomogeneity with respect to tensile & creep strength and ductility across the weld joints. However the mechanical properties of the individual regions of HAZ are difficult to obtain because of the small extent over which each region exists. Welded joints are used as structural parts of boilers and pressure vessels working at high temperatures, hence the main requirement is creep resistance. In the present investigation, the fracture toughness characteristics of base metal and weld metal have been evaluated by CTOD method as per the standard BS 7448. The fracture surfaces of the CTOD tested specimens were examined under Scanning Electron Microscope (SEM). Fractographic studies revealed the mode of failure and the characteristics of the fracture surface.
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