Fatigue Reliability-Based Inspection Planning Methodology for Corroded Mooring Chain Links

Mooring systems are responsible to limit the offsets of oil and gas floating production systems due to environmental actions. Therefore, they are extremely important for the overall safety of the floating unit and of the risers system connected to it. Mooring lines are subjected to pre-tension and environmental loads effects and must be designed to comply with the ultimate, accidental and fatigue limit state criteria. In general, floating units mooring lines are composed by a top chain segment, a rope segment, and a bottom chain segment. Most of the accounted failures in mooring lines are related to fatigue damage in the chain links of the top or bottom segments. Material degradation due to corrosion effects plays an important role in this failure mechanism. Engineering practice usually recommends that a constant corrosion rate model is to be adopted in the design. Periodic inspections are to be carried out in the mooring lines in order to assess the corrosion effects and other issues during the operational life of the floating system. However, corrosion is a complex phenomenon, which behavior is difficult to predict. Adopting a deterministic corrosion rate can lead to non-realistic results, compromising the system safety and the inspection planning. Therefore, to consider the problem uncertainties and comply with standards guidance, this work proposes a time-dependent fatigue reliability-based method to update the inspection planning using the results of previous inspections. The method is applied in a case study of a corroded chain segment of a mooring line, assuming a continuously-updated corrosion rate model and the S-N curve fatigue approach. Results show that the proposed method, based on solid safety assumptions, is a feasible and more reasonable way to define inspection dates, avoiding the mooring system to operate in unacceptable levels of risk.

Identification of Salmonella spp. strains in poultry products and their impact on Public Health

Introduction. Poultry meat and eggs represent a risk of contamination with zoonotic bacterial agents. This requires permanent laboratory monitoring throughout the production chain segment. Material and methods. The research material consisted of samples retrieved from poultry carcasses and eggs for current consumption. There were examined 80 samples of eggs and 110 samples of poultry carcasses. Results. S. Gallinarum, S. Enteritidis and S. Infantins serotypes were isolated in 12.7% of samples out of 110 examined carcasses, whereas S. Gallinarum, S. Dublin și S. Typhimurium serotypes were detected in 6.25% of 80 egg samples. Conclusions. Bacteriological research on poultry carcasses and eggs showed the presence of pathogenic serotypes of Salmonella spp., which is a major risk to public health.

Biodegradable PLA/PBSA Multinanolayer Nanocomposites: Effect of Nanoclays Incorporation in Multinanolayered Structure on Mechanical and Water Barrier Properties

Biodegradable PLA/PBSA multinanolayer nanocomposites were obtained from semi-crystalline poly(butylene succinate-co-butylene adipate) (PBSA) nanolayers filled with nanoclays and confined against amorphous poly(lactic acid) (PLA) nanolayers in a continuous manner by applying an innovative coextrusion technology. The cloisite 30B (C30B) filler incorporation in nanolayers was considered to be an improvement of barrier properties of the multilayer films additional to the confinement effect resulting to forced assembly during the multilayer coextrusion process. 2049-layer films of ~300 µm thick were processed containing loaded PBSA nanolayers of ~200 nm, which presented certain homogeneity and were mostly continuous for the 80/20 wt% PLA/PBSA composition. The nanocomposite PBSA films (monolayer) were also processed for comparison. The presence of exfoliated and intercalated clay structure and some aggregates were observed within the PBSA nanolayers depending on the C30B content. A greater reduction of macromolecular chain segment mobility was measured due to combined effects of confinement effect and clays constraints. The absence of both polymer and clays interdiffusions was highlighted since the PLA glass transition was unchanged. Besides, a larger increase in local chain rigidification was evidenced through RAF values due to geometrical constraints initiated by close nanoclay contact without changing the crystallinity of PBSA. Tortuosity effects into the filled PBSA layers adding to confinement effects induced by PLA layers have caused a significant improvement of water barrier properties through a reduction of water permeability, water vapor solubility and water vapor diffusivity. The obtaining barrier properties were successfully correlated to microstructure, thermal properties and mobility of PBSA amorphous phase.

Polyurethane/Nanosilver-Doped Halloysite Nanocomposites: Thermal, Mechanical Properties, and Antibacterial Properties

In this study, the researchers successfully embellished the surface of halloysite (Ag/HNTs) with silver using halloysite, silver nitrate (AgNO3), and polyvinylpyrrolidone (PVP). The researchers then prepared polyurethane that contained pyridine ring by using 4,4′-diphenylmethane diisocyanate (MDI) and polytetramethylene glycol (PTMG) as the hard chain segment and the soft chain segment of polyurethane (PU), as well as 2,6-pyridinedimethanol (2,6-PDM) as the chain extension agent. This was followed by the preparation of Ag/HNTs/PUs nanocomposite thin films, achieved by mixing Ag/HNTs with different ratios into polyurethane that contains pyridine ring. First, the Ag/HNTs powders were analyzed using energy-dispersive X-ray spectroscopy, X-ray diffraction, and transmission electron microscopy. Subsequently, Fourier-transform infrared spectroscopy was used to examine the dispersibility of Ag/HNTs in PU, whereas the thermal stability and the viscoelasticity of Ag/HNTs/PU were examined using thermal gravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. When the mechanical properties of Ag/HNTs/PU were tested using a universal strength tester, the results indicated a maximum increase of 109.5% in tensile strength. The researchers then examined the surface roughness and the hydrophobic ability of the Ag/HNTs/PU thin films by using atomic force microscopy and water contact angle. Lastly, antibacterial testing on Escherichia coli revealed that when the additive of Ag/HNTs reached 2.0 wt%, 99.3% of the E. coli were eliminated. These results indicated that the addition of Ag/HNTs into PU could enhance the thermal stability, mechanical properties, and antibacterial properties of PU, implying the potential of Ag/HNTs-02 as biomedicine material.

Morphology and crystallization kinetics of Rubber-modified Nylon 6 Prepared by Anionic In-situ Polymerization

In this work, we modified nylon 6 with liquid rubber by in-situ polymerization. The infrared analysis suggested that HDI urea diketone is successfully blocked by caprolactam after grafting on hydroxyl of HTPB, and the rubber-modified nylon copolymer is generated by the anionic polymerization. The impact section analysis indicated the rubber-modified nylon 6 resin exhibited an alpha crystal form.With an increase in the rubber content, nylon 6 was more likely to generate stable α crystal. Avrami equation was a good description of the non-isothermal crystallization kinetics of nylon-6 and rubber-modified nylon-6 resin. Moreover, it is found that the initial crystallization temperature of nylon-6 chain segment decreased due to the flexible rubber chain segment. n value of rubber-modified nylon-6 indicated that its growth was the coexistence of two-dimensional discoid and three-dimensional spherulite growth. Finally, the addition of the rubber accelerated the crystallization rate of nylon 6.

Effect of chain segment length on crystallization behaviors of poly(l-lactide-b-ethylene glycol-b-l-lactide) triblock copolymer

The poly(l-lactide-b-ethylene glycol-b-l-lactide) (PLLA-PEG-PLLA) triblock copolymers with different chain segment length are fabricated by ring-opening polymerization. The structure, molecular weight, and crystallization behaviors of the triblock copolymers are characterized by Fourier transform infrared, nuclear magnetic resonance spectroscopy, gel permeation in chromatography, X-ray diffraction, differential scanning calorimetry, and polarizing optical microscopy (POM). The results show that the increase of block length is beneficial to improve its crystallization. In addition, the triblock copolymer exhibits a double crystallization phenomenon. The POM results indicate that PEG and PLLA chains of the copolymer crystallize in their respective crystallization temperature regions. The growth rate of the PLLA spherocrystal decreases and the dendritic spherocrystals appear with increasing the PEG chain length when the PLLA chain of the copolymer is isothermal crystallized at 80°C and PLLA chain length is constant. The growth rate of the PEG spherocrystal decreases and the spherocrystal morphology changes little with increasing PLLA chain length when the PEG chain is isothermal crystallized at 25°C and the length of PEG chain remained unchanged.