A tribological study of a detonation gun coating of tungsten carbide for use in a subsea gate valve

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Detonation gun coatings of tungsten carbide have been widely recognised as one of the most effective anti-wear coatings for oilfield applications. However, very little fundamental tribological information exists for the material, which hinders coating development and the evolution of correct specifications. This study redresses this problem by conducting adhesive, abrasive and erosive tests upon the coating and relating the findings to the coated microstructure. The intention has been to simulate the in-service behaviour of parallel gate valves, which are used primarily to control flow in remote locations where reliability and freedom from maintenance are essential. Although problems with such valves are rare, costs associated with replacement are exceptionally high and therefore a high research priority has been placed on valves of this type. Currently, new designs of valve are tested using a pipe loop rig at BP Research Centre. However, such tests are both expensive and time consuming and with the increasing desire to bring products to market more quickly an alternative is sought. Probably, the area offering most scope for improvement is in material specification of the sealing surfaces and this work sets out to produce a first stage selection procedure for candidate materials. Uniquely, the study has taken one component, systematically categorised its failure mechanisms using non-destructive replication techniques and then reproduced them in the laboratory. The failure analysis has pointed to three-body abrasion, erosion and adhesion being the dominant failure modes and therefore, a suite of tribo-test methods have been developed to replicate them These are namely reciprocating diamond-on-flat, slurry erosion and reciprocating pin-on-plate tests. The material studied was a proprietary detonation gun coating of tungsten carbide, LW45, which is currently the most popular seal facing material specified for gate valves. A conformal contact geometry was chosen for the reciprocating pin-on-plate tests and problems with alignment were overcome by using a pre-test running-in procedure with 1 μm metallographic paste. Wear of LW45 occurring during the pin-on-plate test was not affected by test speed over the range selected, but was highly dependent upon load. Four different categories ranging from minimal wear to catastrophic wear have been identified. Extensive post test analysis using optical and scanning electron microscopy has further classified the failure that occurs into two groups, termed mild and severe. In the mild regime wear occurs by preferential removal of the binder phase, which is minimised on further sliding by protruding carbide particles. Eventually sufficient binder is removed for carbide fall-out to occur, upon which the cycle is repeated. A greater wear volume is produced by the severe wear mechanism which is caused by the interlinking of cracks present within the microstructure of the coating. To ensure operation in the mild regime, continuous sliding under operating pressures of above 7.84 MPa should be avoided. Abrasive wear simulated by the diamond-on-flat test increased with load. However, the failure mechanisms produced were independent of load and consist of a combination of plastic deformation and brittle fracture with plastic deformation representing the rate controlling step in the wear process. Slurry erosion tests have shown that LW45 wears by a brittle erosive mechanism and is therefore best able to resist erosion at low impingement angles. The volume loss per particle impact for LW45 is proportional to the kinetic energy of the impinging particles. The failure mechanism involved the growth of cracks in the microstructure by a fatigue action eventually leading to crack interlinking and material fall out. For all wear conditions, it is suggested that the removal of microcracking from the coating microstructure will lead to significant improvements in wear performance. A simplified design guide has been produced that gives a weighted importance to the various failure modes attributable to the respective tests. A significant improvement in performance was recorded by LW45 in comparison to typical substrate materials such as AISI 410 and Ferralium F255 stainless steels.SER

Gardner-Webb Review, Volume 1, 1997

Annual publication associated with the Life of the Scholar Multidisciplinary Conference. This publication presents selected essays written by undergraduate students at Gardner-Webb University

The changing policy environment for agriculture in the European Union

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 11. 2010).The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file.Dissertation advisor: Dr Patrick WesthoffVita.Ph.D. University of Missouri--Columbia 2009.The EU has undergone two major expansions in just three years, enlarging from 15 members (EU-15) to 25 members in May 2004, and then adding Bulgaria and Romania in January 2007. Agriculture has played a central role in all the enlargement negotiations as a result of the significant levels of government support in the EU for the sector, the sector's importance in terms of the overall EU budget, and the large number of farmers in the new member states (NMS). A major reform of the Common Agricultural Policy (CAP) was carried out in parallel to the first enlargement, and included changes to the way that agriculture was supported in the EU. Reform of the CAP is ongoing, with a timetable for the elimination of dairy quotas included in the latest reforms. As the link between production and support is broken, the policy most influencing market developments has become that relating to biofuels, whose production and consumption in the EU has expanded rapidly in recent years. In this dissertation, three papers are presented that examine aspects of each of these developments.Includes bibliographical reference

Making the market: How U.S. Policy influences near term agriculture and biofuel industry production and profitability under technology adoption

The beneficiaries of technology adoption in agriculture and biofuels markets in the United States are heavily influenced by domestic biofuel policies and market context. Biofuel mandates, one of the key pillars of domestic biofuel policies, may significantly alter the elasticity of demand for biofuels as well as the derived demand for maize used to produce a significant share of ethanol in the United States. Using a stochastic agriculture and biofuels model, we assess how the introduction of technology may affect the crops and biofuel markets under binding and non-binding biofuel mandates and discuss the implications for analysis of EU biofuel policies.biofuels, policy, technology adoption, mandates, Agricultural and Food Policy, Farm Management, Land Economics/Use,

INCORPORATING BIOFUELS INTO A PARTIAL EQUILIBRIUM MODEL OF THE EU AGRICULTURAL SECTOR

The impact of increased consumption of biofuels on agricultural markets has already been substantial, and will increase further as countries around the world seek to expand the proportion of their energy that they get from renewable sources. Models of the agricultural sector must therefore include some consideration of the demand for agricultural products for biofuels and the byproducts that are produced as part of the production process that are returned to the agricultural sector. In this paper the method of introducing biofuels into the FAPRI GOLD (grains, oilseeds, livestock and dairy) model is discussed. A scenario is run whereby the EU is assumed to introduce a binding 10% target by 2020 and the results are discussed in order to illustrate the workings of the model. The modelling effort is ongoing and planned work is discussed. The aim of the paper is to highlight major issues in building a model of this type.Biofuels, partial equilibrium model, agricultural sector, EU policy, Agricultural and Food Policy, Crop Production/Industries, Research Methods/ Statistical Methods, Resource /Energy Economics and Policy,

Reflections 1996

The 1996 issue of Reflections is edited by Mandy Moonyham with Kevin Binfield serving as faculty adviser. Cover designs are by Jodi Baughn and Robbie Freeman. Award winners of the student poetry contest include: Aubry Moore, Jason McIntosh, and Nicole Hartis. Award winners of the student art contest include: Jodi Baughn, Emily Johnson, Tiffany Faircloth, and Robbie Freeman. Award winners of the student photography contest include: Amanda Williams, Karen Brower, and Heidi Gardner.https://digitalcommons.gardner-webb.edu/reflections/1021/thumbnail.jp

Economic Analysis of Policy Changes in the Beef and Sheep Sectors.

End of Project ReportThe work reported in this document commenced in 1997 under the auspices of the FAPRI-Ireland Partnership. It documents the development of aggregate commodity level models for the beef and sheep sectors, and their subsequent simulation under different policy and macroeconomic environments. Companion reports document the development of similar models for other commodities, and of farm level models

Reflections 1995

The 1995 issue of Reflections is edited by Mandy Moonyham and Heather Love with Kevin Binfield serving as faculty adviser. Cover art is by Sabrina Barnes. Award winners of the student poetry contest include: Karne Brower and Charles Freeman. Award winners of the student art contest include: Sabrina Barnes, Mickie Norman, and Yasuhiro Mori. This year the Communications Department has sponsored a photography contest; winners include: Jason Kerr, Brenda Ledford, and Shawn Childress.https://digitalcommons.gardner-webb.edu/reflections/1020/thumbnail.jp