RESUMEN

The corrosion and leakage issues of rapid quench boilers have become increasingly prominent in ethylene plants, significantly disrupting the regular functioning of equipment. In pursuit of a more efficacious corrosion protection strategy, a study was conducted on the heat exchange tubes experiencing corrosion leakage in the quenching boiler of a petrochemical company. By means of macroscopic observation, chemical composition analysis, mechanical property analysis, metallographic analysis, fracture surface morphology observation, and energy spectrum analysis, combined with on-site process parameters, a comprehensive analysis of the failure causes of the corroded leakage sites was conducted. It was concluded that the perforation of the heat exchange tubes was caused by high-temperature oxygen corrosion and oxidation induced by scale accumulation, and reasonable countermeasures were proposed. According to X-ray diffraction analysis (XRD), it was found that the scale mainly consisted of Fe2O3 and Fe3O4, and the scale formation time was relatively long. It is speculated that the accumulation of scale is caused by the rust from the upstream equipment pipelines of the boiler water being carried into the quenching boiler with the fluid flow and accumulating at this location. Regarding the heat exchange tubes, the primary causes of failure are high-temperature oxygen corrosion and oxidation. To verify whether the relevant reactions can occur spontaneously, the critical transition temperature of the reactions is calculated using the free entropy function method. The calculated critical temperature for the occurrence of high-temperature oxygen corrosion and oxidation in the heat exchange tubes under failure conditions is determined to be T ＜ 1058 K ~ 785 °C. Therefore, under the conditions of heat exchange tube failure, high-temperature oxygen corrosion and oxidation can occur spontaneously.

RESUMEN

Phage infection remains a major cause of fermentation failures in the dairy industry. The development of phage-resistant mutants of important fermentation strains is an effective measure used to address phage-related issues. This study employed the secondary culture method to screen for spontaneous phage-resistant mutants from the phage sensitive strain Limosilactobacillus fermentum IMAU32646 (L. fermentum IMAU32646). The phenotypic characteristics, technological attributes, probiotic characterization, adsorption characteristics and mutant genes were investigated. The results showed that the mutant strain displayed a high degree of phage-resistance and stability. The mutant strain produced more lactic acid during fermentation than the sensitive strain, while maintaining identical cell structure and morphologies. The mutant strain exhibited superior tolerance to acid and bile salts compared to the sensitive strain. Furthermore, the adsorption rate of phage LFP01 on the mutant strain was significantly lower than that of the sensitive strain. Following genome re-sequencing analysis showed that adsorption interference and blocked DNA injection were responsible for its phage-resistance. These results may provide a new strategy for avoiding phage contamination and industrial application of phage-resistant strains with good characteristics.

Asunto(s)

Bacteriófagos , Fermentación , Limosilactobacillus fermentum , Mutación , Limosilactobacillus fermentum/genética , Bacteriófagos/genética , Bacteriófagos/fisiología , Probióticos , Ácidos y Sales Biliares/farmacología , Microbiología de Alimentos

RESUMEN

Limosilactobacillus (L.) fermentum is widely utilized for its beneficial properties, but lysogenic phages can integrate into its genome and can be induced to enter the lysis cycle under certain conditions, thus accomplishing lysis of host cells, resulting in severe economic losses. In this study, a lysogenic phage, LFP03, was induced from L. fermentum IMAU 32510 by UV irradiation for 70 s. The electron microscopy showed that this phage belonged to Caudoviricetes class. Its genome size was 39,556 bp with a GC content of 46.08%, which includes 20 functional proteins. Compared with other L. fermentum phages, the genome of phage LFP03 exhibited deletions, inversions and translocations. Biological analysis showed that its optimal multiplicity of infection was 0.1, with a burst size of 133.5 ± 4.9 PFU/infective cell. Phage LFP03 was sensitive to temperature and pH value, with a survival rate of 48.98% at 50 °C. It could be completely inactivated under pH 2. The adsorption ability of this phage was minimally affected by temperature and pH value, with adsorption rates reaching 80% under all treated conditions. Divalent cations could accelerate phage adsorption, while chloramphenicol expressed little influence. This study might expand the related knowledge of L. fermentum phages, and provide some theoretical basis for improving the stability of related products and establishing phage control measures.

RESUMEN

Limosilactobacillus fermentum is a bacterium widely used in food production, medicine, and industrial fermentation. However, fermentation could fail due to phage contamination. L. fermentum bacteriophage LFP02 can be induced from L. fermentum IMAU 32579 using mitomycin C. To better understand the characteristics of this phage, its physiological and genomic characteristics were evaluated. The results showed that its optimal multiplicity of infection was 0.01, and the burst size was 148.03 ± 2.65 pfu/infective center. Compared to temperature, pH had a more obvious influence on phage viability, although its adsorption capacity was not affected by the divalent cations (Ca2+ and Mg2+) or chloramphenicol. Its genome size was 43,789 bp and the GC content was 46.06%, including 53 functional proteins. Compared to other L. fermentum phages, phage LFP02 had chromosome deletion, insertion, and inversion, which demonstrated that it was a novel phage. This study could expand the knowledge of the biological characteristics of L. fermentum bacteriophages and provide some theoretical basis for bacteriophage prevention during fermentation.

RESUMEN

In this study, the surface of aluminum powder was uniformly coated with in situ reduced graphene oxide (r-GO) sheets (Al/r-GO). The Ni powder, Al2O3 powder, and Al/r-GO powders were mixed uniformly in a mass ratio of 20:6:4. In situ rGO-reinforced Ni-Al intermetallic composite coatings were successfully prepared using low-pressure cold spraying and subsequent heat treatment. The microstructure and phase of the composite coatings were characterized using X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). The high-temperature wear test was conducted at 200 °C, 400 °C, and 600 °C to understand the mechanism. The results indicate that the in situ rGO-reinforced Ni-Al intermetallic composite coatings exhibit a 33.3% lower friction coefficient and 26% lower wear rate in comparison to pure Ni-Al intermetallic coatings, which could be attributed to the generation of an easy-shearing transferred film between the coating and grinding ball.