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

The production of oil and gas offshore developed progressively as the onshore resources and reservoirs were pursued out beyond the low water mark. Particular characteristics of deeper water have resulted in specific and significant engineering features. There are other important issues such as legislation economics and environment that must be considered also. Future changes in offshore engineering including mechanical engineering aspects will probably reflect the recurring challenges of improved safety and cost reduction, as much as those of inadequacies in current performance and of gaps in present capabilities. Brief reference is made to some other exploited and potentially exploitable marine resources which may provide opportunities for technology transfer from the offshore hydrocarbon industry.

The paper begins by highlighting the importance and contributions of the various types of ocean wealth to human well-being. These range from oil, food and minerals to a medium for the transportation of bulk goods and a source of renewable energy. The commercial goal to be satisfied in order to achieve success is then stated and a methodology, based on a tree diagram approach, for identifying ocean market opportunities is described. Four examples relating to support for ocean activities are used to illustrate its application. These deal with underwater navigation systems, intermodal marine transport maritime and offshore safety, and dredging. The criteria for fully realizing the engineering potential are considered. They range from the importance of meeting the commercial goal and the impact of safety on ocean activities to the role of human factors and fresh educational methods. The need for an integrated approach to ocean wealth generation and the contribution of research and development efforts are discussed. The main conclusion is that many other forms of wealth with a potential market as large as that of offshore oil and gas are waiting to be ‘discovered’.

This paper describes a design optimization scheme for systems that require a high likelihood of functioning on demand. The final design specification is achieved by solving a sequence of optimization problems. Each of these problems is defined by assuming some form of the objective function and specifying a sub-region of the design space over which this function will be representative of the system unavailability. An example of a high-pressure protection system has been used to demonstrate the practicality of the technique. Design parameters for this system include redundancy levels, the number of elements required for a voting system to function, component selection options and maintenance inspection intervals. Both implicit and explicit constraint forms have been used in the example. The implicit constraints require a full system analysis to determine whether the current design is feasible or not. All system assessments have been carried out using fault tree analysis.

New legislation following the Piper Alpha disaster has highlighted the unsatisfactory state of programmable equipment system (PES)-based emergency shutdown (ESD) systems for offshore installations. As in the nuclear generation industry, concern is being expressed for the quality of software, particularly project-specific or application software for these systems. The defence-in-depth approach adopted by the nuclear industry is impracticable for the offshore industry and new techniques for design and implementation of the project-specific software of ESD systems are urgently required.

A quick-release door closure design (Bandlock 2) is described. The paper presents a case study of the design and analysis of an existing closure geometry. Four techniques for stress analysis of the closure are described: two numerical (finite element and boundary element) an experimental (electrical resistance strain gauge) and an approximate (strength of materials) approach to the calculation of stresses. The stress results are presented in an unnormalized form for an ANSI class 600 test pressure.

Experimental investigations have been carried out to examine the effect of downstream pipework configurations on the precessing vortex core (PVC) generated within the exhaust region of a cyclone dust separator. Characterization of the PVC using a non-dimensionalized frequency parameter (NDFP) was used to determine the relationship between Reynolds number and geometrical swirl number of the cyclone.

The results show that the NDFP tends towards an asymptotic value for Reynolds numbers of about 50 000 and high swirl numbers (> 3.043). This value is reached earlier with lower swirl numbers. It was concluded that any exhaust pipework configuration produced a significant drop in the PVC frequency, and certain configurations either delayed or promoted the development of the PVC.

Although helical screw compressors contain only two moving parts, their shapes are very complicated and must mesh to very fine clearances. The process of determining lobe geometry requires that parts of the male generate parts of the female and vice versa. Once the nominally perfect (zero clearance) profile geometry has been generated, a method for determining clearances is needed which gives an attainable result from the manufacturing and operational viewpoints and gives a thermodynamic efficiency which is at least equal to that of competing machines of the same class. The thermodynamic performance depends principally on the internal leakage rates in the compressor, in particular, the leakage across the contact (sealing) line.

This paper presents two ways of setting clearances. They result in different patterns of clearance distribution along the sealing line and have different effects of the thermodynamic performance of the compressor due to the different leakage mass flowrates that they permit. A design technique for obtaining an optimum clearance distribution is discussed.

Finally, a thermodynamic model of compressor behaviour is used to predict the performance as influenced by the different clearance distributions, and the predictions are compared with measured values taken from a test compressor. The predictions are shown to be good.

The quarrying industry has a major impact on the environment. The impact arises from direct sources (that is the quarrying operation with attendant noise and dust) and indirect sources (that is electricity usage). To quantify these usages, the quarrying industry in the United Kingdom consumes some 4.8 TW h/year, representing 3 per cent of installed generating capacity. A significant proportion of this usage is attributable to machines known as cone crushers. Cone crushers are large items of plant (up to 3 m diameter) producing, mainly, aggregates for the road-making industry. The British output is currently 230M tonnes per annum, due to rise to 400M tonnes by 2011. The energy costs are currently £240M per annum.

Further environmental issues are raised by the use of manganese steels. A crusher uses, components that can wear away at a rate of 1 mm per hour. If the parts are not renewed at regular intervals machine performance can be dramatically affected and, in the worst case, mechanical damage may occur. The parts are replaced early to avoid damage with a concomitant poor energy utilization.

The paper describes a programme of work intended to address some of these problems. Pegson Limited, a leading manufacturer of crushing plant, in association with Transfer Technology plc and De Montfort University, are co-operating in a project funded by SERC/DTI under the design of high-speed machinery LINK programme, Treatment is theoretical, demonstrating the justification of the funding. A follow-up paper will detail actual savings and contrast them with the theoretical model.

The next generation of crushers will be instrumented with a range of sensors to monitor machine performance. Of especial interest is a novel sensor which monitors the wear of the crushing components The sensors are connected to a knowledge-based system (KBS) to monitor and control performance. The sensors are not reported in any detail due to the pursuance of Intellectual Property Rights. The ideal performance parameters are obtained from another KBS based on rock mechanics and models of wear mechanisms.

The advanced crushers incorporate a simple man/machine interface and make much use of distributed control based on NEC 78K series microcontrollers. Preliminary studies indicate that energy savings of £15M in the United Kingdom (over £400M worldwide) per year are realizable. Further savings of £5M in the United Kingdom (nearly £150M worldwide) per year arise from the optimal use of the manganese crushing components.