The effect of phosphate, fluorine, and soda content of the glass on the mechanical properties of the glass ionomer (polyalkenoate) cements

The authors would like to thank the Department of Trade and Industry, UK, under the project number of TP/5/REG/6/I/H0669A

Materials Selection, Stress Analysis and CFD Modelling of Flare Tips

Oil and gas platforms, refineries and chemical plants need to burn off the excess gas resulting from pressure variations during production. The failure of flare tips, sometimes with short lifetimes, has been a major cause for concern in the oil and gas industry for many years. The aim of this study was to evaluate and improve the performance of flare tips. The study has been approached from two perspectives: (i) material requirements, identifying the most suitable alloys for use in flare tips, and (ii) design optimisation, aimed at the development of a flare tip that minimises interaction with flame, therefore giving lower operating temperatures and longer lifetimes. The thesis also includes an Infra-Red (IR) thermal imaging study to establish flare tip temperature profiles during flaring. Examination of failed flare tips has provided evidence of intergranular oxidation and stress corrosion cracking as possible failure mechanisms. A study of the effect of thermal shock on the oxidation resistance of alloys 800H and 625, currently used in flare tips, is presented. The embrittlement of alloy 625 in the range 650 °C to 800 °C has also been investigated. Thermal imaging of three flares in operation has indicated metal temperatures of up to 1000 °C, above levels that can be sustained by alloys currently in use. A Finite Element model of stress distributions based on the temperature profiles has been developed. It was concluded that flare tip lifetimes would be limited by a combination of creep and fatigue of the support brackets, and by plastic deformation at the top of the windshield. The model successfully predicted the failure of two flare tips and lead to a timely replacement, resulting in significant financial savings and the prevention of catastrophic failure. Commercial Computational Fluid Dynamics software, that solves the Navier-Stokes equation combined with a combustion model, has been used to assess the effect of gas flow rates and wind conditions on combustion behaviour and the resulting operating temperatures of flare tips. The model has been validated with data obtained from thermal imaging studies and shows reasonable agreement, especially at low gas flow rates. As a result, a procedure has been developed to calculate flare tip temperature profiles (via CFD) and mechanical integrity (via FE stress analysis) of flare tips, and thus assess suitability of any flare tip design prior to manufacture and installation

Embrittlement of alloy 625 and effect of remedial treatments

This study investigated the susceptibility of alloy 625 to embrittlement in the temperature range 600–800 ℃ using simulated thermal treatments, specimens from ex-service petroleum industry components and subsequent remedial heat treatment. Embrittlement was quantified by conducting impact testing using the Charpy V-notch method and the results discussed in terms of precipitate formation and ageing. The results of annealing the exposed samples at high temperature are presented, demonstrating that embrittlement is most detrimental at intermediate temperatures (i.e. 650 ℃). The study confirms that a 24-h remedial heat treatment of embrittled alloy 625 leads to significant recovery of impact energy on ex-service samples. </jats:p

Thermal imaging and stress analysis for predicting the behaviour and long-term performance of flare tips

A combination of computational and imaging tools was developed to characterise the performance and assess the lifetime of flare tips, the top portion of stacks used to burn off excess gas in the gas and petroleum industry. Integrating the use of (1) an infrared imaging study to obtain temperature profiles of flare tips in operation and (2) finite element modelling of stress distributions based on temperature profiles allowed lifetime prediction for creep and fatigue failure. The techniques were successfully applied to a complex flare tip design that included a venturi shaped windshield. It was concluded that in this instance, the flare tip lifetime would be limited by a combination of creep and fatigue of the support brackets and by plastic deformation at the top of the windshield. Design methodologies for producing flare tips with improved lifetimes are suggested, including the use of computational fluid dynamics modelling to assess the combined effects of gas flow rates and wind conditions on combustion behaviour. Thus, the prediction prior to installation, of both the performance of a new design and the long-term behaviour, can be a valuable assessment process for a proposed flare tip assembly. </jats:p