Active Corrosion Research Articles

Durable and Hydrophobic Self-Healing Coating with Rapid Thermal Activation and Prolonged Corrosion Resistance

Durable and Hydrophobic Self-Healing Coating with Rapid Thermal Activation and Prolonged Corrosion Resistance

A new sight on the fracture behavior of GH4169 produced by NaCl-induced corrosion in a humid environment of 600 °C

A novel fracture mechanism of GH4169 alloy, produced by active corrosion, was proposed via a slow-strain rate test in a NaCl deposition contained 600 °C humid environment. Circular active corrosion accelerates form of Fe, Cr-depletion and Ni-rich region. The region has elevated stacking fault energy and reduced shear modulus, inhibiting the planner slip yet promoting dislocation tangles ahead of the internal corrosion zone. Localized Stress concentration occurs, facilitating crack propagation. The synergistic interplay between cracking and active corrosion processes accelerates the rupture of GH4169 alloy, leading to reduced ductility and tensile strength of GH4169 alloy in the environments.

Theoretical calculation methods of stable bearing capacity for thin-walled shells with corrosion and variable temperature

AbstractThin-wall shells (steel plates, steel cylindrical shells, steel spherical shells, etc.) are widely used in many engineering fields such as construction, machinery, chemical industry, navigation, and aviation because of their light weight and high strength. Their failure modes under static pressure or impact dynamic load are mostly buckling instability, and the failure is very sudden, often causing structural failure or even catastrophic accidents without obvious symptoms. In this framework, the significance of this paper is that it considers the influence of external environment corrosion on steel shells' bearing capacity using plate and shell classical stability theory, and investigates the stable bearing capacity of thin-wall steel shells in view of corrosion impact. By this approach, a theoretical calculating method for the time-varying stable bearing capacity of plate and shell thin-walled steel members under the simultaneous action of corrosion and temperature changes is obtained, providing a useful theory for complex engineering practices such as corrosion and temperature changes, including fire actions. Noted that for this method with no analytical solution found, its numerical solutions are given in the appendixes.

Аспекты безопасного использования современных дезинфицирующих средств на молочных предприятиях

The article analyzes the main aspects of safe application of chemical disinfectants widely used at dairy enterprises. Effective disinfection at dairy enterprises is directly related to the production of high-quality, safe and competitive food products. When selecting a disinfectant for use at a dairy enterprise, a comprehensive evaluation is necessary not only for effectiveness, but also a multilateral consideration of its safe use. Increasing requirements to ecologization of milk processing enterprises dictate the search for new combinations of functional components in the formulations of chemical sanitizers. The article shows the necessity of consideration of adhesion properties of disinfectants, their corrosive activity and indifference to various materials used at food processing enterprises. It is suggested to control working chloroactive disinfectant solutions, first of all, obtained by electrolysis method, not only by the content of active chlorine, but also by the value of redox potential. The relevance of research aimed at studying the inhibitory properties of active substances and residual quantities of disinfectants on starter microflora and the importance of a systematic approach to the integrated assessment of all elements of safe use of disinfectants at dairy enterprises is formulated. Keywords: disinfectants, toxicity and hazard, effect on human body, environmental safety, redox potential, corrosivity, chemical contamination, inhibition.

Intelligent marine waterborne epoxy coating based on functionalized multiscale nanocomposite: mechanical enhancement, self-reporting, and active/passive anti-corrosion

Corrosion activities and related accidents are significant issues for marine facilities, leading to considerable economic losses. Waterborne epoxy (EP) coating has been seen as one of the optimal options for corrosion protection due to its stable properties and eco-friendliness (0 g/L volatile organic compounds). Nevertheless, several intrinsic deficiencies require improvement, such as fragile mechanical properties and defects (macro and micro), resulting in the continuous deterioration of comprehensive coating performances. In this work, a novel nanocomposite coating with mechanical enhancement, intelligent self-reporting, and active protection is fabricated by integrating the functionalized and compatible graphene oxide/cerium based metal-organic framework multiscale structure (GO-CeMOF-P/M). Notably, the homogenous dispersion of GO-CeMOF-P/M and its chemical interaction with the polymer matrix effectively reduces the defects resulting from solution volatilizing and enhances the compactness, which boosts the tensile strength (32.1 MPa/8.5%) and dry adhesion force (5.8 MPa) of the coating. Additionally, the controllable responsiveness and release of multiscale nanocomposite within external environments endow intelligent active protection and self-reporting characteristics for the GO-CeMOF-P/M-EP coating, making it especially suitable for a variety of practical marine applications. Furthermore, following immersion of 80 d in the aggressive environment, Zf=0.01 Hz value of GO-CeMOF-P/M-EP coating is 1.2 × 1010 Ω·cm2, which is 164.4 times larger than that of EP coating (7.3 × 107 Ω·cm2), demonstrating remarkably strengthened anti-corrosion ability. Consequently, by offering an intriguing design strategy, the current work anticipates addressing the inherent deficiencies of EP coating and facilitating its practicality and feasibility in real sea environments.

Synergistic anti-corrosion and anti-wear of epoxy coating functionalized with inhibitor-loaded graphene oxide nanoribbons

The synergy between corrosion protection and wear resistance is an effective strategy for the development of multifunctional coating to withstand complex working conditions. This study reports an epoxy resin coating filled with benzotriazole loaded metal-organic frameworks (BTA-MOFs) functionalized graphene oxide nanoribbons (GONR) that exhibit active anti-corrosion, act as a barrier to corrosive ion, and enhance wear resistance. The GONR@BTA-MOFs composite is synthesized through chemically etching multi-walled carbon nanotubes and subsequent electrostatic self-assembly corrosion inhibitors loaded MOFs onto the GONR. The composite demonstrates improved compatibility with epoxy resins compared to carbon nanotubes. The anti-corrosion performance of the composite coating is investigated using electrochemical impedance spectroscopy. After immersing in a 3.5 wt.% NaCl solution for 25 d, the alternating current impedance of the composite coating is three orders of magnitude higher than that of pure epoxy resin. Simultaneously, the controlled release of the corrosion inhibitor retards the deterioration of the coating after localized damage occurrence, which functions as active corrosion protection. The GONR@BTA-MOFs/EP composite coating exhibits the highest corrosion potential of -0.188 V and the lowest corrosion current of 3.162 × 10−9 A cm−2) in the Tafel test. Tribological studies reveal a reduction in the friction coefficient from 0.62 to 0.08 after incorporating GONR@BTA-MOFs in the coating, with the wear volume being seven times lower than that of pure epoxy resin. The excellent lubrication effect of the nanomaterials reduces the coefficient of friction of the coating, thereby improving the abrasion resistance of the coating. The synergy between the self-lubrication of the two-dimensional layered fillers and the corrosion resistance of the smart inhibitor containers suggests a promising strategy for enhancing the performance of epoxy resins under complex working conditions.

Structure and Corrosion Behavior of Multiphase Intermetallic ZrCu-Based Alloys.

Zirconium-based alloys are highly regarded by the research community for their exceptional corrosion resistance, thermal stability, and mechanical properties. In our work, we investigated two newly developed alloys, Zr42.42Cu41.18Al9.35Ag7.05 and Zr46.81Cu35.44Al10.09Ag7.66, in the form of ingots and ribbons. In the course of our investigation, we conducted a comprehensive structural and thermal analysis. In addition, an examination of the corrosion activity encompassing electrochemical studies and an analysis of the corrosion mechanisms was carried out. To further evaluate the performance of the materials, tests of their mechanical properties were performed, including microhardness and resistance to abrasive wear. Structural analysis showed that both alloys studied had a multiphase, crystalline structure with intermetallic phases. The samples in the form of ribbons showed improved corrosion resistance compared to that of the ingots. The ingot containing a higher content of copper Zr42.42Cu41.18Al9.35Ag7.05 was characterized by better corrosion resistance, while showing lower average hardness and a higher degree of abrasive wear based on SEM observations after pin-on-disc tests.

Comparing the Corrosion Behavior and Microstructure of a WE43 Mg Alloy in Simulated Body Fluids Under Different CO2 Conditions

With the low density and high specific strength, magnesium (Mg) alloys are lightweight alloys with various applications. In addition, combined with biocompatibility, similar mechanical properties to human bones, and unique biodegradability, Mg alloys are promising biodegradable implant materials for orthopedic surgeries. However, the degradation rates of Mg alloys are too fast in physiological environments, which limits the clinical applications of Mg implants. Therefore, understanding the corrosion behavior in physiological environments is crucial for developing biodegradable Mg alloys.During Mg alloy degradation, hydroxide (OH-) ions are generated, and the pH near the alloy surface increases. Since carbonate-bicarbonate (CO3 2--HCO3 -) is a vital pH buffer system in the human body, the corrosion behavior of Mg alloys would be affected by the CO2 concentrations of the test environments. In this study, we performed electrochemical and corrosion tests of a solution heat-treated WE43 (Mg-4 wt%Y-3 wt%Nd) alloy in Hanks’ balanced salt solutions (HBSS) at 37°C. By performing the tests in air and in an incubator maintained at 5% CO2, the effect of carbonate-bicarbonate pH buffering on the corrosion behavior and corrosion microstructure of the WE43 Mg alloy was investigated.When testing the WE43 Mg alloy in air, a general corrosion morphology was observed during the 24-hour immersion. In contrast, WE43 Mg alloy tested in the incubator shows a more active surface potential and localized corrosion initiates on the alloy surface in the early stages of immersion. Electrochemical impedance spectroscopy (EIS) analysis shows that WE43 Mg alloy tested in air has better corrosion resistance than in the incubator. Furthermore, the corrosion resistance of the alloy tested in air increases with immersion time but decreases when tested in the incubator. Potentiodynamic polarization curves after 24-hour immersion confirm that the corrosion current density (i corr) of the WE43 Mg alloy tested in the incubator is higher than that when tested in air. The difference in corrosion behavior is owing to the carbonate-bicarbonate pH buffering effect and will be discussed based on corrosion microstructure characterizations. Figure 1

Chlorine-Induced Stress Corrosion Cracking of Single Crystal Superalloys at 550 °C

AbstractThis study has investigated the effect of NaCl and different gaseous environments on the stress corrosion cracking susceptibility of CMSX-4 at 550 °C. The presence of SOx leads to the rapid dissociation of NaCl into Na2SO4 and the release Cl2 and HCl, which then trigger an active oxidation mechanism and stress corrosion cracking. The incubation time for crack initiation at 690 MPa and in the presence of a sulphur containing environment is 10 min. A working hypothesis is that stress corrosion cracking occurs due to the hydrogen released at the oxide/alloy interface when metal chlorides are formed; however, this hypothesis needs to be further explored.

Construction of Smart Coatings Containing Core-Shell Nanofibers with Self-Healing and Active Corrosion Protection.

With increasingly severe metal corrosion, coating preparation with high-performance corrosion protection has attracted more attention. Herein, the encapsulation of the corrosion inhibitor 8-hydroxyquinoline (8-HQ) as well as the self-healing agent linseed oil (LO) in polyvinyl alcohol (PVA) and chitosan (CS) shells were realized by coaxial electrospinning, which was recorded as PVA/CS@LO/8-HQ core-shell nanofibers. PVA/CS@LO/8-HQ nanofibers were employed to promote the high-performance corrosion protection of the epoxy coating. The anticorrosion mechanism was that the change of the local pH on the metal surface stimulated the release of 8-HQ from the nanofibers, which were then chelated with iron ions to form a complex. When cracks occurred and caused rupture of the nanofibers, LO was released and reacted with oxygen to cure them so that the cracks could be healed autonomously. The dynamic potential polarization curves showed that the corrosion inhibition efficiency of the compound inhibitor LO + 8-HQ reached 87.54%, 90.31%, and 85.57% at pH = 3, 7, and 11, respectively, higher than that of the single corrosion inhibitor. Density functional theory calculations revealed that the LO and 8-HQ combination, forming a hydrogen bond interaction, promoted the adsorption of inhibitors on the steel surface. Scanning Kelvin probe and electrochemical impedance spectroscopy proved the self-healing corrosion protection properties of the epoxy coating. These results demonstrated that embedding PVA/CS@LO/8-HQ nanofibers in the coating could obtain self-healing properties, and promote the mechanical and corrosion protection of epoxy coating.

Friction stir processing of pure titanium/nanodiamonds nanocomposites: Microstructure, tribological and corrosion properties

A titanium matrix surface nanocomposite with uniformly distributed nanodiamonds was developed using friction stir process for the first time. A dual phase (α+β) microstructure containing ultrafine equiaxed grains was formed within the matrix after three passes. The mean grain sizes were measured to be 0.7 and 0.9 μm for α and β phase, respectively. The stabilization of the β phase at room temperature was discussed, relying on post-processing cooling rate and the diffusion of W elements from the tool to the matrix. The processed nanocomposite exhibited a microhardness value of 618 Hv in the stir zone, which is 4 and 2.6 times to the initial material and pure Ti processed (without nanodiamonds), respectively. Upon friction stir processing of pure titanium (without nanodiamonds), an ultrafine-grained structure with an average size of 2.4 μm was produced, which led to an increase in microhardness up to 238 Hv. Based on conducted tribological evaluations, the processed surface nanocomposite exhibited a significant decrease in friction coefficient and wear weight loss. The results indicated a 47% decrease in friction coefficient and a 75% reduction in wear weight loss compared to the initial material. The investigation of worn surfaces implied that the wear mechanism was altered from delamination in initial pure Ti to abrasive wear in the Ti/NDs processed nanocomposite. Corrosion testing, including electrochemical impedance spectroscopy and potentiodynamic polarization techniques, revealed that Ti/NDs nanocomposite processing mitigated the material corrosion resistance, which were ascribed to the developed ultrafine grained structure as well as NDs nanoclusters to galvanic corrosion activation.

Covalent Transition Metal Borosilicides: Reaction Pathways in Molten Salts for Water Oxidation Electrocatalysis.

The properties of transition metal borides and silicides are intimately linked to the covalent character of the chemical bonds within their crystal structures. Bringing boron and silicon together within metal borosilicides can then engender different competing covalent networks and complex charge distributions. This situation results in unique structures and atomic environments, which can impact charge transport and catalytic properties. Metal borosilicides, however, hold the status of unusual exotic species, difficult to synthesize and with poor knowledge of their properties. Our strategy consists of developing a redox pathway to synthesize transition metal borosilicides in inorganic molten salts as high-temperature solvents. By studying the formation of Ni6Si2B, Co4.75Si2B, Fe5SiB2, and Mn5SiB2 with in situ X-ray diffraction, we highlight how new reaction routes, maintaining covalent structural building blocks, draw a general scheme of their formation. This pathway is driven by the covalence of the chemical bonds within the boron coordination framework. Next, we demonstrate high efficiency for water oxidation electrocatalysis, especially for Ni6Si2B. We ascribe the strongly increased resistance to corrosion, high stability, and electrocatalytic activity of the Ni6Si2B-derived material to three factors: (1) the two entangled boron and silicon covalent networks; (2) the ability to codope with boron and silicon an in situ generated catalytic layer; and (3) a rare electron enrichment of the transition metal by back-donation from boron atoms, previously unknown within this compound family. With this work, we then unveil a new chemical dimension for Earth-abundant water oxidation electrocatalysts by bringing to light a new family of materials.

A novel strategy for constructing active anti-corrosive coatings by embedding three-dimensional fiber networks

The corrosion protection effectiveness of micro/nanocontainer-based intelligent coatings significantly depends on their dispersion within the coating matrix. Inspired by the bionic concept of a ‘vascular network’ we designed a polylactic acid (PLA) three-dimensional fiber network incorporating the pH-responsive TiO2-8-hydroxyquinoline (TiO2-8HQ) nanotubes using electrospinning technology. These TiO2-8HQ@PLA networks are crosslinked and evenly dispersed on the Mg alloy surface, responsive to local pH variations. The encapsulated 8HQ inhibitors release rapidly in alkaline conditions, transporting through the network to enable continuous self-healing in multi-defect areas. An epoxy coating applied over the network forms a novel vascular network intelligent coating. Electrochemical and surface analysis tests reveal that 2 %TiO2-8HQ@PLA-EP provides the most enduring corrosion resistance over 50 days in a 3.5 wt% NaCl solution, with a coating resistance of 2.33 × 106 Ω cm2 and charge transfer resistance of 4.81 × 106 Ω cm2. Additionally, the network enhances adhesion strength (38.01 MPa) and surface wettability (104.25° ± 0.15°), significantly improving the coating’s physical barrier performance. The combination of the micro/nanocontainers technology and vascular network innovative design provides a unique insight into active corrosion control on diverse metals.

Chemical Composition and Properties of Water-Methanol Solution of Formaldehyde

By reacting paraform with methanol and water at concentrations of 10.8, 11.6 and 22.7 mol/l in the presence of catalytic quantities of monoethanolamine, a method was developed for obtaining a bactericide that, at a concentration of 500 mg/l, completely inhibits the formation of hydrogen sulfide in an accumulative culture of planktonic form of sulfate-reducing bacteria with a quantity of 106 cells/ml. The composition of the resulting bactericide, its effectiveness and corrosion properties were studied. Using scanning electron microscopy using a system for energy-dispersive microanalysis, it was shown that the corrosion products formed during the corrosive action of the bactericide on St-20 steel are iron oxides.

The influence of alloying elements segregation on heterogeneous nucleation of TiN on Al2O3 and its local corrosion resistance

A comprehensive study utilizing first-principles calculations has examined the heterogeneous nucleation of TiN on Al2O3 in steel and the impact of alloying elements on this process. Additionally, the study delved into how this nucleation affects local corrosion activity. The findings indicate that alloying elements such as Cr, Mn, Mo, and V tend to concentrate at the Al2O3 (0001)/TiN (001) interface, enhancing the interface's stability, thereby favoring the heterogeneous nucleation of TiN on Al2O3. Consequently, the nucleation leads to the formation of interfaces, namely Al2O3 (0001)/TiN (001) and TiN (100)/bcc-Fe (100), which are less prone to adsorbing chloride ions, replacing the Al2O3(0001)/bcc-Fe (110) interface that can stably adsorb chloride ions, consequently reducing the adsorption of chloride ions at grain boundaries. Moreover, it is difficult for Cr atoms to incorporate into the TiN structure, while Ti atoms readily replace Cr in CrN. TiN exhibits a lower formation energy compared to CrN, and the precipitation of TiN mitigates the formation of Cr-depleted zones, thereby inhibiting local corrosion.

Lawsonia inermis as an Active Corrosion Inhibitor for Mild Steel in Hydrochloric Acid

Corrosion is a pervasive issue affecting metallic materials, with significant economic losses and safety risks in various industries. Mild steel, extensively used in construction and infrastructure, faces corrosion challenges, needing continuous research to effectively tackle them. Natural compounds, because of their eco-friendliness and corrosion inhibition potential, are attracting increasing interest for corrosion control. Lawsonia inermis (LI), or henna, a plant native to North Africa and South Asia, has bioactive compounds exhibiting corrosion inhibitive properties. This study comprehensively explores Lawsonia inermis’s effectiveness as a corrosion inhibitor for mild steel, filling a gap in the existing research. Various concentrations of Lawsonia inermis extract were tested in acidic solutions to evaluate corrosion inhibition. Experimental results indicate a significant reduction in the corrosion rate with increasing inhibitor concentration. Langmuir adsorption isothermal analyses reveal the adsorption mechanism as being an interplay between physisorption and weak chemisorption. Electrochemical measurements demonstrate Lawsonia inermis’s capability to alter both cathodic and anodic reactions, leading to improved corrosion resistance. Scanning electron microscopy reveals a more even surface morphology in the presence of the Lawsonia inermis, indicating corrosion inhibition. Gas chromatography–mass spectrometry (GC-MS) analyses identified organic compounds in Lawsonia inermis extract responsible for corrosion inhibition. Overall, Lawsonia inermis emerges as a promising corrosion inhibitor for mild steel, offering excellent inhibition efficiencies. This study sheds light on its adsorption behaviour and provides insights into its mechanism of action. These findings underscore Lawsonia inermis’s potential as a green corrosion inhibitor, paving the way for its practical application in industrial corrosion protection strategies.

Novel self-healing glass-like CexOY film on a Flash-PEO coated AZ31B Mg alloy

The aim of this work is to develop a glass-like CexOy coating to seal the pores of a Flash-PEO coated AZ31B Mg alloy and simultaneously provide smart self-healing corrosion protection. The cerium sol was synthesized using cerium acetate as main precursor by sol-gel method. SEM micrographs revealed that upon cerium sol deposition, the pores of the oxide coating were effectively sealed, resulting in a double-layer coating system and thereby in a big reservoir of cerium ions (Ce3+/Ce4+). The glassy character of the cerium coating, confirmed by X-Ray diffraction, implies that cerium exists in Ce3+ and Ce4+ ionic states enclosed in a high internal energy structure which facilitate the diffusion of cerium ions to active cathodic zone. Electrochemical Impedance Spectroscopy (EIS), X-Ray Diffraction (XRD), and Raman spectroscopy were used to explore the active corrosion protection of the CexOy sol-gel coating. The corrosion inhibition mechanism involves the migration of cerium ions and the precipitation of insoluble-crystalline cerium compounds (CeO2). The coating demonstrated self-healing properties, presenting a promising alternative to traditional chrome conversion coatings (CCC).

Influence of the activation time of magnesium surfaces on the concentration of active hydroxyl groups and corrosion resistance

Magnesium alloys have been extensively studied as degradable biomaterials for clinical applications due to their biocompatibility and mechanical properties. However, their poor corrosion resistance can lead to issues such as osteolysis and the release of gaseous hydrogen. This study investigated the influence of the activation time of magnesium surfaces in a sodium hydroxide (NaOH) solution on the concentration of active hydroxyl groups and corrosion resistance. The results indicated that immersion time significantly influences the formation of a corrosion-resistant film and the distribution of surface hydroxyl groups. Specifically, specimens treated for 7.5 h exhibited the highest concentration of hydroxyl groups and the most uniform oxide film distribution. Electrochemical tests demonstrated capacitive behavior and passive surface formation for all evaluated times, with the 7.5-h immersion in NaOH yielding superior corrosion resistance, lower current density, and a more efficient and thicker protective film. SEM and EDS analyses confirmed increased formation of Mg(OH)₂ for samples treated for 5 and 7.5 h, while a 10-h treatment resulted in a brittle, porous layer prone to degradation. Statistical analysis using ANOVA and Fisher's LSD test corroborated these findings. The optimal 7.5-h alkali treatment enhanced magnesium's corrosion resistance and surface properties, making it a promising candidate for orthopedic implants. However, further studies are necessary to assess biocompatibility and physiological responses before clinical implementation.

A study on combination of alkaline treatment and PLA/f-CNTs composite coating on corrosion, biocompatibility and antibacterial activity of Mg alloy

The present study explores the effect of combined alkaline treatments (NaOH) and the incorporation of functionalized carbon nanotubes (f-CNTs) into poly(lactic acid) (PLA) composite coatings on the corrosion resistance, biocompatibility, and antibacterial efficacy of AZ31 magnesium (Mg) alloy. Various pretreatment techniques and coating layers have been found to exert considerable influence on the phase composition, morphology, thickness, wettability, as well as corrosion resistance, and biological characteristics of the Mg alloy. The formation of an Mg(OH)2 layer on alkaline-treated Mg alloy has proven to enhance hydrophilicity, corrosion resistance, and biocompatibility. Moreover, the findings highlight that incorporating f-CNTs into PLA improves the corrosion resistance, cytocompatibility, and antibacterial activity of Mg alloy in physiological solutions and the extent of these improvements is related to the quantity of f-CNTs present in the composite coating. Additionally, the outcomes have shown that the inclusion of f-CNTs promotes the formation of carbonate based precipitates during a 14-day immersion in Ringer's solution. Overall, the combination of alkaline treatments and the PLA/f-CNTs composite coating is showcased as a promising surface modification approach for orthopedic applications.

Prediction of Pipe Failure Rate in Heating Networks Using Machine Learning Methods

The correct prediction of heating network pipeline failure rates can increase the reliability of the heat supply to consumers in the cold season. However, due to the large number of factors affecting the corrosion of underground steel pipelines, it is difficult to achieve high prediction accuracy. The purpose of this study is to identify connections between the failure rate of heating network pipelines and factors not taken into account in traditional methods, such as residual pipeline wall thickness, soil corrosion activity, previous incidents on the pipeline section, flooding (traces of flooding) of the channel, and intersections with communications. To achieve this goal, the following machine learning algorithms were used: random forest, gradient boosting, support vector machines, and artificial neural networks (multilayer perceptron). The data were collected on incidents related to the breakdown of heating network pipelines in the cities of Kazan and Ulyanovsk. Based on these data, four intelligent models have been developed. The accuracy of the models was compared. The best result was obtained for the gradient boosting regression tree, as follows: MSE = 0.00719, MAE = 0.0682, and MAPE = 0.06069. The feature «Previous incidents on the pipeline section» was excluded from the training set as the least significant.