Cold-formed circular hollow sections under axial compression

Two series of experiments were carried out to investigate the behaviour of pinned-ended circular hollow section (CHS) columns, subjected to axial compressive load. A total of 30 columns were tested in this investigation; 20 columns in Series 1 and 10 columns in Series 2. The outside diameter-to-thickness ratio (d/t) and the slenderness ratio (KL/r) ranged from 29.7 to 46.4 and 20.8 to 82.2 for Series 1, respectively, and from 55.0 to 62.9 and 10.7 to 34.9 for Series 2, respectively. In general, Series 1 columns failed by overall flexural buckling and, whilst Series 2 columns failed by local ring-type buckling. The test strengths of the columns were compared with the strengths predicted by the South African design standard (SANS10162-1) and the European design standard (EN 1993-1-1)

Investigation into char structure using Raman and petrographic techniques to assess combustion reactivity

Coal petrography, micro Raman spectroscopy (MRS) and thermogravimetric analysis (TGA) were employed to obtain further inside into the evolution of char structure and its reactivity during heat treatment in the temperature range of 300-1400°C on inertinite-rich South African coals. The lack of publications particularly on South African coals, relating Raman spectroscopy to coal petrography and thermogravimetric analyses when investigating the evolution of char structure was a motivation for the study. A laboratory scale Packed Bed Balance Reactor (PBBR) was used to prepare coal char samples at various temperatures; that is 300, 600, 800 and 1000 °C. A drop tube furnace (DTF) was used to prepare chars at 1400°C. Raman spectra of coal and chars were measured on the first-order in the range 800-2000cm-1. Characteristic bonds for amorphous carbons, G band (graphitic) and D band (disorder), were deconvoluted and curve fitted using the OPUS software. Three bands for coal particles were determined; that is the G band at ~1590-1603cm-1, D1 band at ~1343-1355cm-1 and D3 band at ~1507-1557cm-1. Four bands were determined for char particles; that is the G band at ~1590-1603cm-1, D1 band at ~1343-1355cm-1, D3 band at ~1507-1557cm-1 and D4 band at ~1200-1232cm-1. All the bands were fitted with a mixture of Lorentzian and Gaussian functions except the D3 band for which only a Gaussian function was used. It was found that sp2-sp3 bonding (reactive sites/crystallites) occurred in dense chars (originating from inertinite particles) at the initial heat treatment temperature, and these sp2-sp3 bondings are known to be consumed later at high temperature. Earlier consumption of sp2-sp3 bonding was observed in porous chars, since they were vitrinitic in origin and contained more reactive sites. The D1 and G bandwidths showed a significant change with heat treatment, which was consistent with structural modification due to high temperatures. Reflectance measurements, that is: mean vitrinite reflectance (MVR) and mean total reflectance (MTR), showed an increase with heat treatment temperature. MVR and MTR were successfully correlated with Raman parameters (D1 and G bandwidth). MVR and MTR also showed a good correlation with combustion reactivity measured by TGA. Char morphology analyses were carried out petrographically by point counting for quantification and qualification purposes. The char morphology data showed a significant increase in the amount of dense/solid chars as compared to the porous chars with an increase in temperature which is in-line with expectations from the inertinite-rich parent coal. Correlations between the D1 and G bandwidths and char morphology counts were carried out. An inverse of D1 and G bandwidth showed good correlation with the proportion of dense/solid and porous char. It was concluded from this study that the best correlations between Raman spectroscopy and coal petrography was through reflectance measurements, and the identified Raman D1 and G bandwidths. A good linear correlation was also found between Raman D1 and G bandwidths and combustion reactivity. These correlations confirm the strong connection between char structure and its reactivity and illustrate the advantage of Raman spectroscopy in conjunction with coal petrography with respect to other structural analyses. Therefore, the use of MRS and petrography on coal chars enhances the understanding of char structural evolution on a molecular level and may lead to enhanced understanding of pulverised fuel (pf) coal combustion

Application of Organic Petrology and Raman Spectroscopy in Thermal Maturity Determination of the Karoo Basin (RSA) Shale Samples

An assessment performed using raman spectroscopy has found space in the black shales of the Cisuralian-age rocks of the Karoo Basin in South Africa, particularly those from the Guadalupian Ripon, Cisuralian Whitehill and Prince Albert Formations. It is used in conjunction with geochemical screening techniques such as organic petrology and programmed pyrolysis. In turn, the combination of these techniques is used for the assessment of the thermal maturity of the sedimentary organic matter from the perspective of hydrocarbon generation, retention, and expulsion. To provide further understanding of the black shales in the Cisuralian-age rocks of the Karoo Basin in South Africa, this study focuses on the characterization of samples from the KWV−01 borehole drilled in the southeastern Karoo Basin. In addition, the USA Devonian/Carboniferous Berea Sandstone project samples were included for comparison, and were used as a quality assurance measure. Organic petrology was utilized to assess the organic quality and thermal maturity of the black shales. The results obtained showed that the Karoo Basin shales are overmature, containing an abundance of solid bitumen, and this often characterizes a shale reservoir with moveable hydrocarbons (shale gas). The programmed pyrolysis analysis conducted on the black shales of the Karoo Basin yielded artifact results, as they were determined from a very low and poorly defined S2 peak. This indicated the shales to be overmature and categorized them to be of poor hydrocarbon generation potential. Raman spectroscopy was used to gain insights about the molecular structure of the black shales and to assess if this technique could be used as a complimentary tool to determine the thermal maturity of the shale samples. Raman parameters such as G–D1 Band separation, G and D1 band full width at half maximum (Gfwhm and D1fwhm) and G band position were successfully correlated with vitrinite reflectance (RoV), demonstrating a good potential for Raman spectroscopy to predict the thermal maturity of the shales. Overall, the study provides valuable information and knowledge concerning black shale sample characterization (particularly the thermal maturity and molecular structural characterization) in the Karoo Basin, South Africa

Testing reproducibility of vitrinite and solid bitumen reflectance measurements in North American unconventional source-rock reservoir petroleum systems

An interlaboratory study (ILS) was conducted to test reproducibility of vitrinite and solid bitumen reflectance measurements in six mudrock samples from United States unconventional source-rock reservoir petroleum systems. Samples selected from the Marcellus, Haynesville, Eagle Ford, Barnett, Bakken and Woodford are representative of resource plays currently under exploitation in North America. All samples are from marine depositional environments, are thermally mature (T \u3e445 °C) and have moderate to high organic matter content (2.9–11.6 wt% TOC). Their organic matter is dominated by solid bitumen, which contains intraparticle nano-porosity. Visual evaluation of organic nano-porosity (pore sizes \u3c 100 nm) via SEM suggests that intraparticle organic nano-pores are most abundant in dry gas maturity samples and less abundant at lower wet gas/condensate and peak oil maturities. Samples were distributed to ILS participants in forty laboratories in the Americas, Europe, Africa and Australia; thirty-seven independent sets of results were received. Mean vitrinite reflectance (VR ) values from all ILS participants range from 0.90 to 1.83% whereas mean solid bitumen reflectance (BR ) values range from 0.85 to 2.04% (no outlying values excluded), confirming the thermally mature nature of all six samples. Using multiple statistical approaches to eliminate outlying values, we evaluated reproducibility limit R, the maximum difference between valid mean reflectance results obtained on the same sample by different operators in different laboratories using different instruments. Removal of outlying values where the individual signed multiple of standard deviation was \u3e1.0 produced lowest R values, generally ≤0.5% (absolute reflectance), similar to a prior ILS for similar samples. Other traditional approaches to outlier removal (outside mean ± 1.5*interquartile range and outside F10 to F90 percentile range) also produced similar R values. Standard deviation values \u3c 0.15*(VR or BR ) reduce R and should be a requirement of dispersed organic matter reflectance analysis. After outlier removal, R values were 0.1%–0.2% for peak oil thermal maturity, about 0.3% for wet gas/condensate maturity and 0.4%–0.5% for dry gas maturity. That is, these R values represent the uncertainty (in absolute reflectance) that users of vitrinite and solid bitumen reflectance data should assign to any one individual reported mean reflectance value from a similar thermal maturity mudrock sample. R values of this magnitude indicate a need for further standardization of reflectance measurement of dispersed organic matter. Furthermore, these R values quantify realistic interlaboratory measurement dispersion for a difficult but critically important analytical technique necessary for thermal maturity determination in the source-rock reservoirs of unconventional petroleum systems. max o o o