During LNG storage and transportation by ship, a fraction of the LNG in the cryogenic tanks evaporates due to heat ingress through the insulation, resulting in boil-off gas (BOG) production and a change in LNG composition, a phenomenon known as LNG ageing. Common practice is to assume that BOG composition and related density are identical to the initial LNG or pure methane, resulting in inaccuracy in BOG mass flow measurements. This is particularly important regarding LNG shipping economics and the utilization of BOG as a fuel for ship propulsion. This work investigates the influence of LNG ageing on the produced BOG thermodynamic properties relevant to the mentioned inaccuracies’ estimation and correction. An established, simplified, dynamic boil-off model is utilized for the simulation of LNG and BOG properties’ changes during the voyage. Four cases represented by limiting the minimum and maximum values of methane and nitrogen content are used to estimate the general influence of the compositional variability over the whole range of practically possible LNG source mixtures. Research results provide an insight into the relevant BOG properties’ variability and confirm that BOG flow measurements should be corrected with dynamic model simulations results due to significant differences between the total BOG mixture and forced BOG mixture corresponding to the LNG composition.

The most commonly used subsea pipeline installation method is the S-Lay method. A very important and complex task in an S-Lay installation engineering analysis is to find the optimal pipelay vessel installation configuration for every distinctive pipeline route section. Installation loads in the pipeline are very sensitive to small changes in the configuration of the pipeline supports during laying and other influential parameters, such as the tensioner force, stinger angle, trim and draft of the pipelay vessel. Therefore, the process of an engineering installation analysis is very demanding, and there is a need for an automated optimization process. For that purpose, installation engineering methodology criteria and requirements are formalized into a nonlinear optimization problem with mixed continuous and discrete variables. A special tailored multi-objective genetic algorithm is developed that can be adjusted to any desired combination of criteria and offshore standards’ requirements. The optimization algorithm is applied to the representative test cases. The optimization procedure efficiency and quality of the achieved solution prove that the developed genetic algorithm operators and the whole optimization approach are adequate for the presented application.

This study provides a comparative analysis of non-destructive testing (NDT) and destructive testing (DT) applied to MAG welding of dissimilar AISI316L and DH36 steels using K-309LT filler wire. The welding process, performed in vertical and horizontal positions on a ceramic support, was optimized for mechanical integrity. NDT techniques such as ultrasonic, visual and penetrant testing, enabled the detection of internal and superficial defects such as porosity, lack of fusion and cracks without affecting the test samples. However, they did not provide information on mechanical performance under load. DT methods, including tensile, impact, bending and hardness tests, provided critical data on weld structural integrity, toughness, ductility and the effects of heat input on the microstructure, particularly in the fusion and heat-affected zones. These destructive tests confirmed the nature of the defects, detected, and assessed their impact on the performance of the weld. The study concludes that, while non-destructive testing is essential for preliminary quality control, it should be complemented by DT for a complete understanding of weld behavior under service load. The synergy of both approaches is crucial to ensure safety, durability and optimal performance of welded structures made of different steels.

Single-number ratings are widely used in building acoustics, but they are meaningful only when the reference-curve procedure is applied correctly and the reported descriptors are matched to the physical problem. This study re-evaluates accredited in situ measurements of airborne and impact sound insulation for a timber-frame interfloor construction at the Archaeological Museum of Istria, Croatia. Applying the measured one-third-octave spectra in 1 dB reference-curve steps according to ISO 717 gives R′w = 55 dB and L′n,w = 62 dB. Both values satisfy the historical Croatian requirements that applied at the time of measurement. For the meeting-room source context, the ISO 717-1 adaptation term C = −3 dB gives R′w + C = 52 dB; Ctr is not used in the internal-partition analysis because it represents a low-frequency-rich, traffic-oriented source spectrum. The impact receiving-room volume is 95.4 m³. A separate diffuse-field scenario estimates how certified broadband absorption would change the unnormalized receiving-room level Li(f); it is not treated as a change in L′n,w, and no band-by-band 60 dB compliance threshold is applied. A separate sensitivity analysis of floating-floor resonance gives f0 = 28–89 Hz over the selected mass–stiffness range, with an as-built estimate of about 53 Hz. The paper therefore distinguishes measured apparent sound insulation, source-spectrum context, receiving-room response, and analytical sensitivity without presenting the scenario calculations as validated acoustic optimization.

A CT-80 coiled tubing fractured at the gooseneck during retrieval after a 2.5 h treatment with 15% HCl under high-temperature bottom-hole conditions (196 °C). The failure was investigated by dimensional measurements, metallography, Vickers microhardness testing, SEM/EDS, and FT-IR spectroscopy. Pronounced corrosion asymmetry was observed. Cumulative external wall loss reached 1.196 mm, compared with 0.292 mm on the inner wall, while the wall loss attributed to the final operation was approximately twelve times greater externally than internally. These findings suggest two different exposure histories: predominantly uniform attack of the outer wall during backflow of spent, inhibitor-depleted acid, and localized pitting of the inner wall under incomplete inhibitor coverage. EDS mapping identified Sb-rich deposits around inner-wall pits. In combination with the relevant literature, this distribution is consistent with a possible Sb–Fe galvanic effect that may have promoted local anodic dissolution, although galvanic coupling was not measured directly. The FT-IR spectra were consistent with iron oxides/oxyhydroxides, carbonate-containing scale, sulfate-bearing products on the outer surface, and thin organic residues rather than a continuous inhibitor film. Microhardness increased from 229 HV1 in the new tubing to 243.4 HV1 at the fracture location; this increase may reflect limited hydrogen uptake together with service-induced strain hardening or residual stresses. Fractography showed necking and dimpled microvoid coalescence, supporting a predominantly ductile overload mechanism in the corrosion-thinned section. A limited contribution of hydrogen to ductility loss cannot be excluded because the hydrogen content was not quantified.