Pipeline Instrumentation: The British Gas National Transmission System

The transmission and distribution system operated by British Gas plc is the largest integrated pipeline system in Europe. The whole system comprises a national transmission system which carries gas from five terminals to the twelve gas regions. Each region in turn carries the gas through a regional transmission system into a distribution grid and thence onto its customers. The national, regional and distribution system all present the instrument engineer with different technical challenges because of the way in which they have been built and are operated, however, it is simplest to characterise them by their process conditions. The operating pressure is highest in the national transmission system being up to 75 bar, in the regional transmission system the pressure is usually less than 37 bar, and in the distribution grid it is less than 7 bar. In general, the pipe diameters decrease from the national system downwards, and the measured flowrates are lowest in the distribution grids. This paper is concerned only with instrumentation on the national transmission system. The discussion will cover current technology which is typical of that being installed at present, and concentrates on the more commonly found instrumentation. The paper begins with a brief history of development of the national transmission system and a description of how it is operated. This is followed by a discussion on the application of computers to the control of unmanned installations. A section concerning the measurement of pressure and its application to the control of the system comes next. The main part of the paper contains an analysis of high accuracy flowmetering and the paper concludes with some comments on developments in instrumentation and their application to changing operation of the national transmission system.

Centralized Control Techniques for the Citrus Concentrating Plant

There is a strong tendency within the citrus industry to regard the citrus concentrating plant as being a series of discrete operations. From the viewpoint of the instrument engineer the process is a continuous one, incorporating three major dead time areas: (a) the fruit bins, (b) the surge (evaporator feed) tanks, and (c) the tank farm At all other points in the process the product can be treated as a continuous flow. Paper published with permission.

Measurement of Orifice Plate Edge Sharpness

A significant factor which affects the accurate prediction of the discharge coefficients of square edged orifice plates is the precise shape of the edge. A rounding of only 0·002 of the orifice diameter can increase the coefficient by 1% so that a reliable method of assessing the edge sharpness is of considerable benefit to the instrument engineer. In the work described in this paper, a systematic intercomparison of three methods of measuring orifice edge sharpness has been undertaken. The methods tested involved casting, lead foil impression and optical techniques, and their relative reliability and effectiveness has been assessed. While the results obtained from the casting and lead foil methods showed good agreement, the foils did not follow the edge profiles as closely as the castings. The casting procedure can also be used to determine the shapes of re-entrant profiles which will not be detected using lead foil impressions. However, the casting method required more skill and considerably more time to complete measurements than the impression method. The optical method proved to be the least reliable, since measurements depended on subjective judgment. Nevertheless, this measuring procedure could be completed more quickly than the others, and these tests indicated that it may be used to examine large diameter plates for burrs or excessive rounding.

A Rating Formula for Fine Pitch Boundary Lubricated Gears

For the Instrument Engineer involved in the design of mechanisms that transmit power under boundary lubricated conditions, little information is available on which to base fine pitch gear load capacity and life. This paper discusses a gear test program and the development of a rating formula for the surface loading of these gears, and in particular those made from stainless steel and aluminum and stocked by precision gear manufacturers.

Instrumenting for Computer Control

An instrument engineer outlines some of the answers to problems encountered in the design, specification, installation, startup, and maintenance of an instrumentation system for a computer-controlled potash ore plant. Putting the emphasis on the computer/instrument interface, most of this user's statements are general and applicable to any ddc installation.