Proceedings of the Institution of Mechanical Engineers,Part E: Journal of Process Mechanical Engineering

The industrial approach to designing relief valves does not use fundamental physics to its best advantage. Consideration of dimensions and synthesis of the separate aspects of the design are shown to reduce the performance testing needed during development. The valve is modelled as a convergent-divergent nozzle of variable area ratio, controlled by fluid and system dynamics. Flow and force characteristics have been produced which suggest a new design philosophy. A report is made of completed and ongoing work aimed at demonstrating the benefits of using flow and force characteristics for design and development of high-lift relief valves, which are mainly used under conditions of compressible flow.

This paper presents an investigation of the cyclic loading on oilfield drill strings due to longitudinal, torsional and lateral vibrations and compares this with the ‘statical’ cyclic loading caused by a deviated string at a dog-leg. Such cyclic loading is a principal contributor to drill string fatigue failures. The methodology of the paper uses numerical dynamic analyses of longitudinal and torsional vibrations together with quasi-static models for lateral vibration and dog-legs to compare the cyclic loading induced separately by each of these effects. A linear damage law (that is Miner's rule) is used to calculate the resultant fatigue damage from the cyclic loading. The results of this investigation show that longitudinal and torsional vibrations may induce significant cyclic loading comparable to that from typical dog-legs whereas the influence of lateral vibration is small. The longitudinal and torsional vibrations are strongly influenced by rotary speed and damping coefficients and can induce significant cyclic loading and rapid accumulation of fatigue damage on drill pipes and collars.

The selection of a shell-and-tube heat exchanger type and geometry is one of many engineering applications, where a wide range of specialized knowledge is available as qualitative rules that can be incorporated in an expert system.

This paper presents a technique used for building a knowledge-base system utilizing object-oriented expert system shells. The described steps of system development are: identifying the sources of information, building the knowledge base and finally the production of the runtime program.

The constructed prototype system assists the designer in making decisions about fluid allocation, selection of TEMA (Tubular Exchanger Manufacturers Association) shell type, bundle, heads and various geometrical details. The ultimate aim of developing an expert system of this type is to achieve an integrated design procedure covering all considerations from initial selection to the final thermohydraulic and mechanical design.

This paper is concerned with the development of a design methodology for glass-reinforced plastic (GRP) pipework and fittings. As the use of GRP material becomes more widespread procurement is being increasingly carried out on a performance basis against specified pressure ratings. This is analogous to schedules in metallic piping systems. However, there are, as yet, no design methods available that are able to relate the test data obtained in the measurement of long-term performance under simple internal pressure conditions to the wider requirements of pipe components in service. The most significant outstanding issue is the effect of material anisotropy and the need to cater for the wide variety of possible loading situations present in a typical piping layout. In this paper a rationale is presented based on a simple analysis which employs a limited range of measured data to derive an allowable design envelope. This is then used to develop a qualification procedure which can be used to establish pressure ratings and takes into account the behaviour of GRP materials under likely imposed loads.

The use of vibration to reduce residual stress levels in fabrications is potentially an attractive alternative to thermal annealing. The application of the process has hitherto been limited by the lack of coherent theory of operation. In this study, residual stresses were introduced into a low-alloy steel EN3b by rolling. It was shown that prolonged low-amplitude vibration at 100 Hz induced a stress relaxation of as much as 40 per cent, where the original level was close to yield. A model has been developed to explain the diverse effects resulting from low-amplitude vibration; the model involves the motion of dislocations under the influence of the combined residual and external cyclic stress fields. This model, which has been validated by detailed X-ray line profile analysis and elasticity measurements, is an extension to the currently available explanation for VSR (vibratory stress relief). The standard model, which assumed the need to exceed the local yield stress, only comes into operation at the higher levels of applied stress amplitude. The development of accurate and validated methods for the application of VSR may now be contemplated.

The die drawing of polymers in the solid state is now an established process for achieving molecular orientation in drawn products and an enhancement of their mechanical properties. A mechanics analysis is presented of the drawing of polypropylene through strain rate controlled dies, where the strain rate is either constant, increasing at a uniform rate or decreasing through the die. The stress in an element of material being drawn is determined from equilibrium considerations and application of the Tresca yield criterion. Flow stress data are deduced from uniaxial stress-strain-strain rate tests and applied to the problem using equivalent stress-strain concepts.

Results are presented of axial stress, flow stress and die wall pressure throughout the dies and show that polypropylene can prematurely leave contact with the die wall, particularly in decreasing strain rate dies at high drawing speeds. Increased friction of the die wall and increased drawing speed cause this ‘loss of contact’ point to move progressively downstream in all die cases. Theoretically predicted drawing loads show acceptable agreement with experimental test results when low values of friction coefficient are assumed.

In this paper the dependence of the power consumption of pneumatic conveyors upon conveyed materials, pipeline route and bore, and mode of flow has been examined. The findings are that, with different materials and modes of flow, not only is the amount of power consumed very different but it varies in different ways with pipe bore and routing. Additionally it has been found that, for any given conveying system, the choice of air mover also has a strong influence on the power requirement.