Evaluation of Failure Capacity of Offshore Riser Protectors Under Vessel Impact

Conventional riser protectors, also known as riser-guards, are installed on fixed offshore platforms to protect risers from vessel impact. These space frame structures made of hollow mild steel tubular sections are mainly designed using the approach of boat fenders which may result in over- or under-protection provided to risers. Lack of in-depth study on the dynamic behavior and capacity of conventional riser-guards is considered to be the primary challenge for creative and efficient design of conventional riser protectors. This paper presents a detailed numerical investigation on the dynamic response, damage and failure mechanics of conventional steel riser-guards during accidental vessel collision using nonlinear finite element analysis. Collision forces equivalent to vessel collision with riser-guards for different spans were estimated to provide information for load-based design. Variation in damage patterns for broadside and bow impacts is presented for riser protectors with different spans. The actual capacity of a typical riser-guard in terms of maximum impact energy sustainable prior to failure was also determined from dynamic pushover analysis. The structural response and damage parameters presented in this study can be used for better understanding of damage mechanism and failure capacity of riser protectors which can act as a baseline for further design optimization, as well as the development of other alternative riser protection systems.     

Effect of filler surface treatment on mechanical properties and thermal properties of single and hybrid filler–filled PP composites

The influence of two types of surface treatments (aminosilane and Lica‐12) on the mechanical and thermal properties of polypropylene (PP) filled with single and hybrid filler (silica and mica) was studied. An improvement in tensile properties and impact strength was found for both treatments compared to those of untreated composites. However, the filler with silane coupling agent showed better improvement compared to the filler with Lica‐12 coupling agent. This was due to better adhesion between filler and matrix. Thermal analysis indicates that surface treatments increased the nucleating ability of filler, but decreased the coefficient of thermal expansion of PP composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of structural changes of silica filler on the coefficient of thermal expansion (CTE) of underfill encapsulant

This study investigates the effect of degree of crystallinity (DC) of silica on the CTE value of epoxy filled silica composite. Various DC of silica was produced through high intensity grinding process in a jet mill by varying the grinding pressure. The ground silica with the DC ranging from 76% to 100% was filled at 45% volume and the CTE values were measured. The obtained results showed that CTE of composite was reduced as the filler's degree of crystallinity decreased.     

Preparation of iron oxide nanoparticles by mechanical milling

Hematite powder (Fe₂O₃) was ground in a planetary mill and the milling time and mill rotational speed were varied at three levels. The ground products were then characterized, to investigate size reduction and the mechanochemical effect, by X-ray diffraction (XRD) line broadening, specific surface area (SSA) and particle size and morphology analysis. The line broadening technique was used to determine the degree of crystallinity, crystallite size and lattice strain. The milled hematite particles revealed particle sizes in the nanometer range with a specific surface area of 14.96 m²/g. All milled samples exhibited the mechanochemical effect, where the degree of crystallinity ranged from 9.37 to 49.8%. The minimum crystallite size obtained was 17.1 nm with a degree of crystallinity of 9.37% when hematite was ground at 600 rpm for 10 h.     

Single and hybrid mineral fillers (talc/silica and talc/calcium carbonate)‐filled polypropylene composites: Effects of filler loading and ratios

Properties of single and hybrid fillers with polypropylene (PP) composites were studied in this research work. The effect of filler loadings of three types of mineral fillers, namely talc, silica, and CaCO₃, was investigated. In hybrid composites systems, the effect of silica/talc (SI/T) and CaCO₃/talc (CC/T) filler ratios at 40 wt% was determined. Generally, the results demonstrated that SI/T has higher modulus than CC/T but both hybrids did not have a significant effect on PP strength. In thermal properties, both hybrids have a nucleating ability as they increase the crystallization temperature and onset of crystallization temperature of PP. Results of analysis by TGA revealed that SI/T increased thermal stability of PP composites more than CC/T. Better flammability of the SI/T system is exhibited by lower burning rates of SI/T than CC/T, which indicates better thermal stability of the hybrid system. J. VINYL ADDIT. TECHNOL., 20:160–167, 2014. © 2014 Society of Plastics Engineers     

Effect of single‐mineral filler and hybrid‐mineral filler additives on the properties of polypropylene composites

The present study was carried out to determine the filler characteristics and to investigate the effects of three types of mineral fillers (CaCO₃, silica, and mica) and filler loadings (10–40 wt%) on the properties of polypropylene (PP) composites. The characteristics of the particulate fillers, such as mean particle size, particle size distribution, aspect ratio, shape, and degree of crystallinity were identified. In terms of mechanical properties, for all of the filled PP composites, Young's modulus increased, whereas tensile strength and strain at break decreased as the filler loading increased. However, 10 wt% of mica in a PP composite showed a tensile strength comparable with that of unfilled PP. Greater tensile strength of mica/PP composites compared to that of the other composites was observed because of lower percentages of voids and a higher aspect ratio of the filler. Mica/PP also exhibited a lower coefficient of thermal expansion (CTE) compared to that of the other composites. This difference was due to a lower degree of crystallinity of the filler and the CTE value of the mica filler. Scanning electron microscopy was used to examine the structure of fracture surfaces, and there was a gradual change in tensile fracture behavior from ductile to brittle as the filler loading increased. The nucleating ability of the fillers was studied with differential scanning calorimetry, and a drop in crystallinity of the composites was observed with the addition of mineral filler. Studies on the hybridization effect of different (silica and mica) filler ratios on the properties of PP hybrid composites showed that the addition of mica to silica‐PP composites enhanced their tensile strength and modulus. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers     

Value adding limestone to filler grade through an ultra-fine grinding process in jet mill for use in plastic industries

In this study, ultra-fine grinding of limestone was carried out in jet mill using four levels of classifier rotational speed and grinding pressure. The holdup amount was determined during the grinding process, while the feed rate was kept constant at 8 kg/h. The ground product was characterized for its particle size and shape. In addition, the mechanochemical effect on the ground product was characterized through XRD. The particles size of the ground product ranged from 2.21 μm to 7.29 μm, demonstrating various particle shapes such as cubical, angular, and elongated. The degree of crystallinity of the ground product ranged from 54.5% to 93.7%. Afterwards, the ground product was incorporated as filler in polypropylene (PP), and its performance was characterized for mechanical properties. After conducting the test work, we find that the PP filled with ground limestone exhibited excellent thermal and mechanical properties. The composite flexural modulus, impact strength, tensile strength, and elongation at break were 2.1 GPa, 42 kJ/m², 22.75 MPa, and 21%, respectively, when loaded up to 20%. It likewise exhibited CTE value of 57.2 ppm/°C.     

Titanium Carbide Reinforcement in Iron Matrix Through Carbothermal Reduction of Mechanically Milled Hematite and Anatase

This study investigated the influence of the duration of milling on the formation of TiC-reinforced iron composite through carbothermal reduction of a hematite and anatase mixture. Mixtures of hematite, anatase, and graphite powders were mechanically activated in a planetary ball mill in an argon atmosphere with different milling times (0 to 60 hours). X-ray diffraction showed that with increasing milling time, the crystallite size of the hematite decreased to nanometer range, accompanied by an increment in internal strain. Prolonging the milling process increased dislocation density of the as-milled powder. The as-milled powder was consolidated by cold pressing under 100 MPa and sintered in vacuum at 1373 K (1100 °C). High temperature during sintering resulted in the formation of iron and titanium carbide phases as confirmed by X-ray diffraction, scanning electron microscope, and energy dispersive X-ray analysis. Without mechanically activated milling, the reaction forming TiC did not occur during sintering at 1373 K (1100 °C), indicating a reduction in reaction temperature promoted by mechanical milling. An increase in milling time resulted in an increase in sintered density and hardness due to the fineness of the composite powder, together with complete TiC and iron phase formation.