Failure Analysis and Prevention

Ruxanda R.

McDougall J., Cline K., Hopkins P., Counts S.

Lightning strike damage to domestic water piping is not well documented in technical literature, and there are few resources available to assist investigators. This study describes the failure of a ¾-inch copper water pipe embedded in the concrete foundation of a residence, triggering an insurance claim. To determine whether the failure was lightning-related, the pipe underwent a detailed metallurgical evaluation. The analysis revealed distinct physical features, including an irregularly shaped perforation with curled-in edges surrounded by a halo. Limited metallographic evidence was revealed during the evaluation including gradual wall loss from the exterior surface of the halo toward the perforation and a superficial heat-affected exterior layer within the halo. Some features found during this investigation vary from the reference reviewed, therefore adding to physical features that can guide in investigations where lightning strike is suspected.

Yaagoob I.Y., Goni L.K., Ossoss K.M., Mazumder M.A., Ali S.A., Alfantazi A., Verma C.

This work aims to synthesize, characterize, and assess the ability of a novel tosylate-based dicationic surfactant (EDBT4) to inhibit mild steel corrosion in a 15% HCl solution (pickling solution). The surfactant was synthesized using well-established methods and characterized using various analytical techniques, including FT-IR, NMR (1H and 13C), GC–MS, and TGA. These techniques validated the surfactant’s purity and structural elucidation. Weight loss, PDP, and EIS measurements examined the synthesized dicationic surfactant’s inhibitory efficiency. The outcomes indicate that EDBT4 is a highly effective corrosion inhibitor, demonstrating the highest efficiency of 95.0% at a concentration of 20 ppm. SEM, EDX, and XPS surface analysis techniques investigate the inhibition mechanism and provide information about the protective film that forms on the metal surface. The study explores the corrosion inhibition mechanism through potentiodynamic polarization in more detail and finds that EDBT4 is a mixed-type inhibitor. Based on the acquired data, EDBT4 adsorption on the metal surface follows the Langmuir isotherm model. The study also emphasizes the application of density functional theory (DFT)-based computational simulations, highlighting the critical roles played by the sulfonyl group (SO2) and aromatic ring (C6H4‒) on the charge sharing and adsorption of EDBT4. This DFT study clarifies the molecular interactions between the produced surfactant and the metal surface and offers a complete understanding of the surfactant’s performance as a corrosion inhibitor.

Jiang W., Zhu K., Li J., Qin W., Zhou J., Li Z., Gui K., Zhao Y., Mao Q., Wang B.

In present work, tensile behaviors of cold-rolled 304L stainless steel were investigated at both room temperature (RT) and liquid nitrogen temperature (LNT). After cold-rolling with a thickness reduction of ∼92%, the 304L stainless steel exhibits an ultrahigh yield strength of 1787 MPa at the expense of ductility (1.06% of uniform elongation) at RT. At LNT, the yield strength (upper yield point of σyu = 2308.4 MPa and lower yield point of σyl = 1894.2 MPa) and uniform elongation (23%) increase greatly. Detailed microstructural investigation reveals that the cold-rolled 304L stainless steel comprises mainly of deformation induced martensite and high density of dislocations (9.06 ×1014 m−2), leading to a lack of dislocation storage capacity and thus brittle fracture at RT. While interrupt tests at LNT reveal a first increase and then decline in dislocation density with tensile strain, accompanied with phase transformation from austenite to martensite. The delamination events also occur, characterized by the multiple separated laminated ligaments observed at fracture surface. Therefore, the high dense dislocations and transformation-induced plasticity (TRIP) effect as well as delamination toughening mechanism contributes to the excellent combination of strength and ductility at LNT. Our work provides experimental and microstructural insights into the deformation mechanisms of the ∼92%-cold-rolled 304L stainless steel during tensile deformation at RT and LNT.

Zimmermann N., Wang P.H., Pullen K.

Aircraft accident investigations are paramount for the continuous improvement of aviation safety. As such, maximizing the amount of evidence that can be gathered from an accident site is critical. However, with composites being increasingly used for the construction of airframes, additional challenges are introduced into the handling of debris. Specifically, composites under combustion are known to release potentially noxious fibers and gases, posing a threat to individuals in the surrounding area. In response thereto, so-called fixant solutions (also referred to as hold-down solutions) can be used to minimize the release of inhalable fibers. Nonetheless, researchers have highlighted the risk for these solutions to interfere with the accident investigation process by masking, altering or even destroying fractographic features needed to determine the source or sequence of composite failures. Consequently, literature calls for more research focused on characterizing the influence of fixant solutions on the failure analysis of aeronautical composites. In this study, the impact of one form of fixant solution – namely, wetted water (i.e., water with a surfactant) – is evaluated. A [(0/90)]8 woven carbon fiber/epoxy composite sample is damaged in tension (representing an aircraft accident-causing failure), burnt (simulating an accident site fire) and doused in a wetted water fixant solution. The fracture surface is subsequently evaluated via a scanning electron microscope (SEM) and the condition of fractographic features relevant to the failure analysis is qualitatively evaluated. Through the findings of the study, a better understanding of the impact of a fixant solution on the failure analysis conducted during an aircraft accident investigation can be obtained. Moreover, the results can be used to develop protocols related to the handling of burning composites aiming to maximize both, the safety of individuals involved as well as the evidence needed to conduct a thorough investigation into the causal factors of an accident.

Elbeltagy A., Xu Z., Shen X., Krupp U., Song W.

Kishore K., Kushwaha S., Sai Pranay Teja K., Kumar Chandan A., Mukherjee M., Adhikary M., Kumar A.

Traveling grates (TG) are used as beds over which green pellets are subjected to a series of thermal cycles, namely preheating, induration, and firing to make the pellets suitable for charging in the blast furnaces of an integrated steel plant. In this work, chronic failures of TG links after a service life of 2.5–3 years are investigated. A comparative analysis of failed, used and new TG links was carried out. Fractography of the failed link revealed an intergranular brittle fracture near the surface followed by a transgranular fracture with a signature of decohesion in the bulk of the fracture surface. Microstructural analysis revealed the presence of pre-existing grain boundary chromium carbides (Cr23C6) in the new (unused) link, which can facilitate easy crack initiation and propagation. Furthermore, failed and used TG link revealed the presence of extensive precipitation of needle-like sigma phase confirmed by a combination of X-ray diffraction and scanning electron microscopy coupled with energy dispersive spectroscopy techniques. Such precipitation of the sigma phase occurs during exposure to a susceptible high-temperature range. The presence of the sigma phase is known to embrittle the austenitic stainless steel and such embrittlement is confirmed by a significant increase in hardness and decrease in Charpy impact toughness of failed and used TG links compared to the new TG link. Thermodynamic and kinetic simulations confirmed a high susceptibility of the existing alloy composition to extensive sigma phase precipitation in a wide temperature range. A new alloy composition with higher nickel (∼30 wt%) and free from tungsten is proposed to reduce the susceptibility towards in-service embrittlement induced by sigma phase precipitation.

Passos T.A., Costa H., Luz F.K., Pintaude G.

Soil preparation tools are subject to severe abrasion. The wear resistance of various industrial components can be improved using the hardfacing technique. The improvement in hardfacing wear resistance depends on the microstructure, i.e., the chemical composition of the alloys, the method of overlay, and the parameters of the selected process. The Plasma Transferred Arc with Powder (PTA-P) welding process is interesting as a hardfacing technique since it promotes very low dilution of the substrate in the coating. In this article, the PTA-P welding process was used for the deposition of Fe-Cr-C-based hard coatings with the addition of vanadium onto cheap and relatively soft low-carbon steel substrates. Rubber-wheel abrasion tests were performed to compare the abrasion resistance between commercial anti-wear steel and weld-deposited Fe-Cr-C-V hard coatings. In addition, the microstructure, dilution, and wear mechanisms were investigated. The dilution of the coatings affected the microstructure, in particular, the free mean path of the vanadium carbides, but it only affected abrasion resistance when the wear mechanism involved rolling abrasion. The deposited coatings proved to be at least three times stronger than a commercial abrasion-resistant steel due to the distribution and morphology of the vanadium carbides formed in the coatings.

Giacomin R.C., Bollinger A.L., Komolwit P., Natarajan T.T., Pistorius P.C., Webler B.A.

High Si concentrations in third-generation advanced high-strength steels (AHSS) are known to cause cracking in continuous cast slabs during cooling at temperatures below 300 °C. To investigate the mechanism connecting Si to this embrittlement, impact toughness tests are conducted on as-cast Fe–0.2C–3.0Mn steels with 0.5, 1.5, and 3.0 wt% Si at temperatures between 100 and 400 °C. The propagation path of the cracks through the microstructure of the specimens is examined. The ductile-to-brittle transition (DBT) behaviors of the three steels are compared. Higher Si concentrations raise the DBT temperature of the steels. The influence of Si on both solid-solution strengthening and autotempering during cooling likely contributes to this by increasing the hardness of these as-cast microstructures. In addition, the precipitation of pro-eutectoid ferrite (αPE), which is promoted by higher Si concentrations, significantly lowers the upper shelf energy of the DBT curve. The αPE phase also alters the propagation path of brittle fracture in the specimens, potentially contributing to the increase in DBT temperature. The increase in DBT temperature and decrease in upper shelf energy may contribute to the as-cast AHSS slab embrittlement at low temperatures observed in the industry.