Revealing the Microstructural Aspects of the Corrosion Dynamics in Rapidly Solidified Mg-Zn-Y Alloys Using the Acoustic Emission Technique

This work was focused on revealing the relation between the microstructure and corrosion dynamics in dilute Mg97.94Zn0.56Y1.5 (at.%) alloys prepared by the consolidation of rapidly solidified (RS) ribbons. The dynamics of the corrosion were followed by common electrochemical methods and the acoustic emission (AE) technique. AE monitoring offers instantaneous feedback on changes in the dynamics and mode of the corrosion. In contrast, the electrochemical measurements were performed on the specimens, which had already been immersed in the solution for a pre-defined time. Thus, some short-term corrosion processes could remain undiscovered. Obtained results were completed by scanning electron microscopy, including analysis of a cross-section of the corrosion layer. It was shown that the internal strain distribution, the grain morphology, and the distribution of the secondary phases play a significant role in the corrosion. The alloys are characterized by a complex microstructure with elongated worked and dynamically recrystallized α-Mg grains with an average grain size of 900 nm. Moreover, the Zn- and Y-rich stacking faults (SFs) were dispersed in the grain interior. In the alloy consolidated at a lower extrusion speed, the homogeneous internal strain distribution led to uniform corrosion with a rate of 2 mm/year and a low hydrogen release. The consolidation at a higher extrusion speed resulted in the formation of uneven distribution of internal strains with remaining high strain levels in non-recrystallized grains, leading to inhomogeneous growth and breakdown of the corrosion layers. Therefore, homogeneity of the internal strain distribution is of key importance for the uniform formation of a protective layer.

REINFORCEMENT OF AGEING SHIP STRUCTURES

The objective of the present study is to investigate the possibility to recover the ultimate strength of a rectangular steel plate with a manhole shape opening subjected to a uniaxial compressive load and non-uniform corrosion degradation reinforced by additional stiffeners. Finite element analyses have been carried out to verify the possible design solutions. A total of four finite element models are generated, including 63 sub-structured models. The non-uniform corrosion has been generated by the Monte Carlo simulation. The reinforcement process covers three scenarios that include mounting of two longitudinal stiffeners, two longitudinal and two transverse stiffeners and the flange on the opening. The positioning of the stiffeners has also been studied. A total of 10 cases has been selected and tested for the numerical experiment. Three different assessments have been performed to evaluate the ultimate strength, weight and cost. Two additional studies on the effect of the plate thickness and slenderness have been also carried out.

PENGARUH KADAR SALINITAS AIR TERHADAP LAJU KOROSI BAJA ST 60

Daerah perairan dapat menimbulkan risiko serangan korosi yang lebih tinggi terutama pada lingkungan perairan yang mengandung salinitas atau salinitas, umumnya korosi yang terjadi di perairan dapat menyerang logam, salah satunya adalah baja ST 60 yang banyak digunakan sebagai bahan konstruksi dalam konstruksi bangunan. pelabuhan, jembatan, poros baling-baling, dan aplikasi lain yang terkait dengan lingkungan perairan. Dampak yang ditimbulkan adalah logam dapat mengalami serangan korosi dengan cepat akibat berinteraksi dengan lingkungan air yang mengandung salinitas sehingga logam tersebut akan mengalami kerusakan dan kehilangan sifat teknisnya. Pada penelitian pengujian perendaman dilakukan dengan 3 minggu terus menerus dan 3 minggu (dengan 2 minggu perendaman kemudian 1 minggu tidak terendam) menggunakan air laut yang berasal dari pantai takisung, pelaihari dengan salinitas 2,48% dan air payau yang berasal dari dataran tinggi banjarmasin dengan salinitas 1,25%. Hasil penelitian menunjukkan laju korosi tertinggi terjadi pada 3 minggu perendaman terus menerus dengan air laut yang memiliki salinitas 2,48% dan jenis korosi yang terbentuk adalah korosi seragam. Water areas can pose a higher risk of corrosion attack, especially in aquatic environments that contain salinity or salinity, generally corrosion that occurs in the waters can attack metals, one of which is ST 60 steel which is widely used as construction material in the construction of ports, bridges, propeller axis, and other applications related to the aquatic environment. The impact caused is that the metal can experience corrosion attacks quickly due to interacting with the water environment containing salinity so that the metal will experience damage and lose its technical properties. In the study immersion testing was carried out with 3 weeks continuously and 3 weeks (with 2 weeks immersion then 1 week not submerged) using seawater originating from takisung beach, pelaihari with salinity of 2.48% and brackish water originating from the high land area of banjarmasin with a salinity of 1.25%. The results showed the highest corrosion rate occurred at 3 weeks of continuous immersion with seawater which had a salinity of 2.48% and the type of corrosion formed was uniform corrosion.

Effect of Grain Refinement on the Corrosion Resistance of 316L Stainless Steel

The effect of hydrostatic extrusion (HE) on the microstructure, uniform corrosion, and susceptibility to a localized attack of 316L stainless steel was studied. Both qualitative and quantitative analyses of inclusions before and after HE were carried out. The multiplication of non-metallic inclusions after HE lowered the stability of the passive film over a broad range of pH, while refinement of the matrix had a minor effect on it. The refined materials were prone to metastable pitting, but their pitting corrosion resistance was improved.

Analysis of Temperature Variations, Types of Insulation and Coating on Corrosion Under Insulation on ASTM A53 Pipes

Corrosion Under Insulation (CUI) can be described as localized corrosion that forms as a result of the penetration of water or moisture through an insulating material. The pipe material used is of the ASTM A53 standard and the fluid used in seawater because almost all industries are located on the coast. This type of coating is carried out on the test pipe using Meiji Epoxy Filler. The test method is carried out by flowing seawater fluid in pipes with water temperature variations of 30°C, 50°C, and 70°C. This pipe varies the type of insulation by using glasswool and Rockwool (ASTM G 189-07). This insulation is conditioned in a wet state by giving 2 ml of seawater drops with a pH value of 4 per 6 hours. The test equipment is divided into 3 series according to temperature variations with 4 test specimens and 2 coating variations respectively. The test time was carried out for 336 hours to obtain the corrosion rate results using the ASTM G31-72 weight loss method. The results showed that the type of Glasswool insulation with specimens coated had the lowest corrosion rate value of 0.00483 mmpy at a temperature of 30°C when compared to the same type of treatment on Rockwool insulation of 0.00724 mmpy or an increase of 2.41 times. This study shows that the type of insulation, temperature variation, and coating greatly affect the rate of corrosion and the type of corrosion that occurs is uniform corrosion.

Lateral torsional buckling capacity of corroded steel beams: A parametric study

Thickness reduction due to uniform corrosion increases the tendency of lateral torsional buckling (LTB) of open cross-sections and it reduces the moment capacity of the beam. The effect of the various corrosion cases on the LTB moment capacity (M b,rd) of the I-beams are investigated in this paper. An analytical framework for patch corroded I-beams is introduced to provide a guideline for simulating the nonlinear lateral torsional buckling behaviour of patch corroded simple beams. Hence the effect of different corrosion scenarios to reduce the buckling reduction factor (η LT) is investigated by conducting a parametric study. Twelve different beam lengths were considered to obtain different non-dimensional slenderness ratios (λ LT) in this parametric study. The degraded buckling curves were obtained for each corrosion scenarios.