Risk-based process safety assessment and control measures design for offshore process facilities

Process operation is the most hazardous activity next to the transportation and drilling operation on an offshore oil and gas (OOG) platform. Past experiences of onshore and offshore oil and gas activities have revealed that a small mis-happening in the process operation might escalate to a catastrophe. This is of especial concern in the OOG platform due to the limited space and compact geometry of the process area, less ventilation, and difficult escape routes. On an OOG platform, each extra control measure, which is implemented, not only occupies space on the platform and increases congestion but also adds extra load to the platform. Eventualities in the OOG platform process operation can be avoided through incorporating the appropriate control measures at the early design stage. In this paper, the authors describe a methodology for risk-based process safety decision making for OOG activities. The methodology is applied to various offshore process units, that is, the compressor, separators, flash drum and driers of an OOG platform. Based on the risk potential, appropriate safety measures are designed for each unit. This paper also illustrates that implementation of the designed safety measures reduces the high Fatal accident rate (FAR) values to an acceptable level.     

Corrosion fatigue crack initiation and growth in 18 Ni maraging steel

Nucleation of fatigue cracks in air and 3.5 wt% NaCl solution has been studied in an 18 wt% Ni maraging steel. Specimens tested on reverse bending fatigue machine showed a marked decrease in fatigue strength of the steel in NaCl solution reducing the 10⁷ cycles endurance limit from 410 MPa in air to 120 MPa. Microscopic studies revealed crack initiation to be predominantly associated with non-metallic silicate inclusions in both cases. In air, initiation is caused by decohesion of the inclusion/matrix interface, while in NaCl solution complete detachment of inclusions from the matrix results due to the dissolution of the interface. 70% more inclusions are quantitatively shown to be associated with cracks in NaCl solution than in air at the same stress levels. Experimental and theoreticalS-N curves and inclusion cracking sensitivity data are consistent with the mechanism suggested. The final fracture occurs by the main crack consuming the inclusions ahead of it by the “unzipping” of the shear band produced between the crack tip and the inclusion ahead.     

Studies on Herbaceous Seed Oils III

Seed oils from seven species belonging to four botanical families have been analysed for their fatty acid composition by using chromatographic and spectroscopic techniques. Oils from six species are very interesting in containing high percentage (63.7–84.0%) of C₁₈ unsaturated acids. Chemical screening of seed oils reveals that the species producing highly unsaturated oils merit attention for evaluation as perspective crops.     

Decolorization of textile effluent by bitter gourd peroxidase immobilized on concanavalin A layered calcium alginate-starch beads

Bitter gourd peroxidase immobilized on the surface of concanavalin A layered calcium alginate-starch beads was used for the successful and effective decolorization of textile industrial effluent. Effluent was recalcitrant to the action of bitter gourd peroxidase; however, in the presence of some redox mediators, it was successfully decolorized. Effluent decolorization was maximum (70%) in the presence of 1.0mM 1-hydroxybenzotriazole within 1h of incubation. However, immobilized bitter gourd peroxidase showed maximum decolorization at pH 5.0 and 40 degrees C. Immobilized bitter gourd peroxidase decolorized more than 90% effluent after 3h of incubation in a batch process. The two-reactor system, one reactor containing immobilized peroxidase and the other had activated silica, was quite effective in the decolorization of textile effluent. The system was capable of decolorizing 40% effluent even after 2 months of continuous operation. The absorption spectra of the untreated and treated effluent exhibited a marked difference in absorbance at various wavelengths. Immobilized peroxidase/1-hydroxybenzotriazole system could be employed for the treatment of a large volume of effluent in a continuous reactor.     

Effect of browning reaction products of phospholipids on autoxidation of methyl linoleate

Methyl linoleate was allowed to autoxidize in bulk phase at 50 C in the presence of either synthetic phospholipids consisting of saturated fatty acids or egg yolk phospholipids to estimate the effect of base group and fatty acid moiety of phospholipids on oil autoxidation. Dipalmitoyl phosphatidylcholine (DPPC) and dipalmitoyl phosphatidylethanolamine (DPPE) exhibited poor antioxidant activity at 50 C and showed no synergistic effect with α-tocopherol. The addition of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) of egg yolk accelerated the oxidation of methyl linoleate. However, egg yolk PC and PE collected at various stages of heating at 180 C inhibited hydroperoxide formation at the initial stage of oxidation. This effect could be attributed to the browning products formed during heating reaction. Thus, browning color products formed from unsaturated phospholipids at high temperatures may influence oil stability, although the base group of phospholipids did not exert any significant effect.     

Thermal Compatibility of Concrete and Composite Reinforcements

Experiments on commercially-produced composite reinforcements have shown that the transverse coefficients of thermal expansion (CTE) of these rebar are 3–5 times higher than the CTE of concrete. In this paper, thermoelastic solutions of plain and spirally wrapped composite rebar, embedded in concrete and subject to a uniform temperature increase, are presented. Comparisons are made between bars with no spiral wrapping and those produced with a spiral wrap of unidirectional rovings. Results show that the spiral wrapping, included primarily to improve the bond between the concrete and the composite rebar, also aids in the reduction of overall thermal expansion of the rebar. Thermoelastic solutions of unidirectional composite rods and concrete predict that the tensile stresses in the concrete surrounding the rebar will exceed the tensile strength of the concrete for relatively small temperature increases. The extent of this cracking cannot be determined from the analytical predictions. To predict the extent of the cracking, nonlinear thermoelastic simulations, completed using the COSMOS-M finite-element code, are used to determine the extent of concrete cracking. Results show that cracking decreases with a decreasing rebar diameter and increasing confining pressure of the concrete.     

Optical properties of a-(Se70Te30)100−x(Se98 Bi2)x thin films

Measurements of optical constants (absorption coefficient, refractive index, extinction coefficient, real and imaginary part of the dielectric constant) have been made on a-(Se₇₀Te₃₀)_100−x (Se₉₈Bi₂)_x thin films (where x=0, 5, 10, 15 and 20) of thickness 2000 Å in the wavelength range 450–1000 nm. It is found that the optical bandgap decreases with the increase of Se₉₈Bi₂ concentration in the a-(Se₇₀Te₃₀)_100−x(Se₉₈Bi₂)_x system. The value of refractive index (n) decreases, while the extinction coefficient (k) increases with increasing photon energy. The results are interpreted in terms of concentration of localized states varying effective Fermi level.     

Optical band gap and optical constants in a-Se100–xSbx thin films

Abstract

The optical properties of a-Se_100-xSb_x thin films (where x = 0, 0.5, 2.5, 5 and 10) have been studied in the wavelength range 540–900 nm. It was found that the optical band gap increases with increasing Sb concentration in the a-Se_100-x Sb _x system. The refractive index n decreases, while the extinction coefficient k increases with increasing photon energy. DC conductivity measurements of a-Se_100-x Sb _x thin films have been reported in the temperature range 349–375 K. It has been observed that the conductivity increases while the activation energy decreases with increasing Sb concentration. We correlated the optical band gap with the electronegativity of the sample. The band gap increases with the decrease in electronegativity of each sample of a-Se_100-x Sb _x .     

Toward the Discovery of a Novel Class of Leads for High Altitude Disorders by Virtual Screening and Molecular Dynamics Approaches Targeting Carbonic Anhydrase

For decades, carbonic anhydrase (CA) inhibitors, most notably the acetazolamide-bearing 1,3,4-thiadiazole moiety, have been exploited at high altitudes to alleviate acute mountain sickness, a syndrome of symptomatic sensitivity to the altitude characterized by nausea, lethargy, headache, anorexia, and inadequate sleep. Therefore, inhibition of CA may be a promising therapeutic strategy for high-altitude disorders. In this study, co-crystallized inhibitors with 1,3,4-thiadiazole, 1,3-benzothiazole, and 1,2,5-oxadiazole scaffolds were employed for pharmacophore-based virtual screening of the ZINC database, followed by molecular docking and molecular dynamics simulation studies against CA to find possible ligands that may emerge as promising inhibitors. Compared to the co-crystal ligands of PDB-1YDB, 6BCC, and 6IC2, ZINC12336992, ZINC24751284, and ZINC58324738 had the highest docking scores of −9.0, −9.0, and −8.9 kcal/mol, respectively. A molecular dynamics (MD) simulation analysis of 100 ns was conducted to verify the interactions of the top-scoring molecules with CA. The system’s backbone revealed minor fluctuations, indicating that the CA–ligand complex was stable during the simulation period. Simulated trajectories were used for the MM-GBSA analysis, showing free binding energies of −16.00 ± 0.19, −21.04 ± 0.17, and −19.70 ± 0.18 kcal/mol, respectively. In addition, study of the frontier molecular orbitals of these compounds by DFT-based optimization at the level of B3LYP and the 6-311G(d,p) basis set showed negative values of the HOMO and LUMO, indicating that the ligands are energetically stable, which is essential for forming a stable ligand–protein complex. These molecules may prove to be a promising therapy for high-altitude disorders, necessitating further investigations.     

Field and Laboratory Evaluation of the Thermo Electron 5020 Sulfate Particulate Analyzer

The Thermo Electron Model 5020 Sulfate Particulate Analyzer is a recently commercialized instrument that provides continuous measurements of the sulfate component of ambient particulate matter. The technique uses a stainless steel rod placed inside a quartz oven to reduce the particle sulfate to sulfur dioxide; followed by pulsed fluorescence detection of the sulfur dioxide. Field and laboratory evaluations of a pre-production version of the analyzer are described as well as laboratory evaluations of the pre-production version and two production units. Laboratory tests concentrated on challenging the instruments with ammonium sulfate aerosol, but tests with sodium, potassium, and calcium sulfate are reported as well. The instrument performed very well in field and laboratory settings, reporting values that were highly correlated with continuous mass measurements in the lab, and 24-hour filters in the field. Conversion/detection efficiencies for ammonium sulfate in the laboratory, and for ambient sulfate aerosol at our rural site in Addison, New York, were both very close to 80%. Laboratory conversion efficiencies for calcium, sodium, and potassium sulfate salts ranged from 4% to 63%. These lower efficiencies for mineral-type sulfates will be an important consideration in areas with significant concentrations of sea salt or mineral dust sulfate, and less important for the high sulfate Eastern US which is dominated by ammonium sulfate.