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This study investigates the stress corrosion cracking (SCC) behavior of type 316L stainless steel (SS316L) produced with sinter-based material extrusion additive manufacturing (AM). Sinter-based material extrusion AM produces SS316L with microstructures and mechanical properties comparable to its wrought counterpart in the annealed condition. However, despite extensive research on SCC of SS316L, little is known about the SCC of sinter-based AM SS316L. This study focuses on the influence of sintered microstructures on SCC initiation and crack-branching susceptibility. Custom-made C-rings were exposed to different stress levels in acidic chloride solutions at various temperatures. Solution-annealed (SA) and cold-drawn (CD) wrought SS316L were also tested to understand the SCC behavior of SS316L better. Results showed that sinter-based AM SS316L was more susceptible to SCC initiation than SA wrought SS316L but more resistant than CD wrought SS316L, as determined by the crack initiation time. Sinter-based AM SS316L showed a noticeably lower tendency for crack-branching than both wrought SS316L counterparts. The investigation was supported by comprehensive pre- and post-test microanalysis using light optical microscopy, scanning electron microscopy, electron backscatter diffraction, and micro-computed tomography.

There is a fast-growing interest in the use of selective laser melting (SLM) for metal/alloy additive manufacturing. Our current knowledge of SLM-printed 316 stainless steel (SS316) is limited and sometimes appears sporadic, presumably due to the complex interdependent effects of a large number of process variables of the SLM processing. This is reflected in the discrepant findings in the crystallographic textures and microstructures in this investigation compared to those reported in the literature, which also vary among themselves. The as-printed material is macroscopically asymmetric in terms of both structure and crystallographic texture. The and crystallographic directions align parallel with the SLM scanning direction (SD) and build direction (BD), respectively. Likewise, some characteristic low-angle boundary features have been reported to be crystallographic, while this investigation unequivocally proves them to be non-crystallographic, since they always maintain an identical alignment with the SLM laser scanning direction, irrespective of the matrix material’s crystal orientation. There are also 500 ± 200 nm columnar or cellular features, depending on the cross-section, which are generally found all over the sample. These columnar or cellular features are formed with walls made of dense packing of dislocations entangled with Mn-, Si- and O-enriched amorphous inclusions. They remain stable after ASM solution treatments at a temperature of 1050 °C, and therefore, are capable of hindering boundary migration events of recrystallization and grain growth. Thus, the nanoscale structures can be retained at high temperatures. Large 2–4 μm inclusions form during the solution treatment, within which the chemical and phase distribution are heterogeneous.

Jacketing or a weather barrier is usually installed in insulated piping systems and pressure vessels to prevent water ingress and protect the insulation. In the event of water penetration and accumulation resulting from poor design and/or aging of the jacketing, drain holes are proposed to accelerate the water dry-out process. This study investigated the influence of jacketing and drain holes on corrosion under insulation of carbon steel. In an enclosed system without the drain holes, where the water dry-out process is reduced, the underlying steel remains exposed to the corrosive environment for a longer period of time. Severe pitting corrosion was observed, which could be a result of limited oxygen diffusion into the insulation creating differential aeration environments favorable for pitting corrosion. The presence of drain holes promoted the water dry-out rate and oxygen diffusion into the insulation. As a result, the average corrosion rate increased in short-term exposure tests, but over a longer term the average corrosion rate, as well as the pitting rate, decreased.

Specimens were additively manufactured in 316L stainless steel (SS316L) with a technology that combines the extruding method of fused filament fabrication (FFF) with the strengthening stages of metal injection moulding (MIM). A thorough metallographic analysis and tensile testing were carried out to investigate the effect of sintering in the final microstructures, mechanical properties, and fracture modes of the manufactured material. SS316L wrought specimens were also characterised and tested for comparison. Results showed that the sinter-based technology produced a near-fully dense material with a porosity of 1.27% v/v, and a microstructure and mechanical properties comparable to the standard requirements of the UNS S31603 grade. The sintered specimens were characterised at as annealed condition, with fully austenitic microstructures, annealing twins, and sintering defects such as (1) scattered round microporosity, (2) elongated macroporosity, (3) spherical inclusions rich in Si, Mn and O —also found in the precursor powder— and (4) irregular inclusions rich in Cr, Mn and O. The average mechanical properties of the printed SS316L were Young’s modulus (E) 196 GPa, 0.2% offset yield strength (Sy) 166 MPa, tensile strength (Su) 524 MPa, elongation after fracture 85% and reduction of area 51%. Based on the findings, a mechanism is outlined explaining the departure from the typical cup-and-cone ductile fracture in the necked region observed in the printed samples.

Purpose - To study and compare the inhibition effects of eco-friendly inhibitors of sodium silicate and 1-hydroxyethylidene 1,1 diphosphonic acid (HEDP) in corrosion control and prevention of soft water discolouration (red water) in carbon steel pipelines.Design methodology approach - Electrochemical impedance and Tafel polarization measurements were used to study corrosion inhibition properties. The experiments were carried out under different concentration ratios of inhibitors. Different hydrodynamic conditions were applied to simulate pipeline fluid flow. Scanning electron microscopy (SEM) and EDAX analysis were used for surface studies.Findings - It was observed that corrosion inhibitor combinations under static conditions showed synergistic effects at low concentrations. The inhibition efficiency and synergistic behaviours of inhibitors were enhanced as the electrolyte turbulence was increased. In addition, the inhibitor concentration value required to reach maximum inhibition decreased. It was found that at 20 ppm sodium silicate and 5 ppm HEDP, co-inhibition efficiencies increased significantly to more than 90 per cent and the corrosion rate decreased far below 1 mpy as the electrode rotational speed was increased. Surface studies using SEM revealed the formation of a compact and uniform film of co-inhibitors.Practical implications - The results of this paper can be used for the development of effective, non-toxic and economically attractive corrosion inhibitor formulations for soft water transmission pipelines.Originality value - The observed synergistic behaviour can be due to the incorporation of the silicate gel-like network through organic phosphorous bonds. The hydrodynamic condition of the electrolyte leads to enhancement of inhibition efficiency, which indicates that the corrosion inhibition was mass transfer controlled.

Electrical conductivities and densities of acidic zinc, cadmium and manganese sulphate solutions were measured. Empirical equations have been derived to represent the measured values with high accuracy. Electrical conductivity of solutions has been shown to be expressed as a logarithmic function of temperature, a second order polynomial function of sulphuric acid concentration and a linear function of metal ion concentration. It can be deduced that the density of solution can be described as a linear function of metal ion concentration, temperature and sulphuric acid concentration. These equations could be used to improve the electrowinning or electrorefining process conditions.

A test method for low-level dissolved oxygen (DO) measurement in glycol-based conditions is explained. Three independent DO measurement techniques are compared in water-only and monoethylene glycol (MEG) solutions. The objective is to determine limitations and advantages of each technique when the measurement is performed in MEG.