Practical Experience Case Histories

Chapters 2-5 end with some lists of case histories, often with details of the life to date or to first maintenance. These case histories mainly relate to zinc coatings, where corrosion resistance is the prime requirement, but also to zinc roofs and to cast zinc in some specific aggressive situations. 

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Sharing the Experience booklets 2003-2004 are now available to refinery and chemical process employees for a wide range of topics of interest. BP is currently reinvigorating the series, but as of this time it is not distributed via the normal book sales route (I do not think it ever was). These superb booklets cover fundamentals and are backed up by numerous case histories of hard-learned lessons. They are chock-full of easily understood illustrations and up-to-date color photos. The Sharing the Experience booklet series is a practical, timeless process safety masterpiece that should be available in every control room. The booklet on the hazards of water was first published about 50 years ago and improved to perfection. 

This observation is very important because it points to a way to consider this memory as a qualitative attribute of system B (the environment or the bath) that determines the physical behavior of system A. In the example of Eq. (7.50), where system B comprises one degree of freedom Z2, its dynamics is solely determined by its interaction with system A represented by the coordinate zi, and the memory can be as long as our observation. In practical applications, however, system A represents only a few degrees of freedom, while B is the macroscopic surrounding environment. B is so large relative to A that its dynamics may be dominated by interactions between B particles. Our physical experience tells us that if we disturb B then leave it to itself, it relaxes back to thermal equilibrium with a characteristic relaxation time tb. In other words, B forgets the disturbance it underwent on this timescale. If this remains true also in the case where A and B interact continuously (which says that also in this case tb is dominated by the internal dynamics of B), then the state of B at time t does not depend on disturbances in B that were caused by A at times earlier than t = t — tb- Consequently, dynamics in the A subspace at time t will depend on the history of A at earlier times going back only as far as this t. The relaxation time tb can be therefore identified with the memory time of the environment B. 

The use of the lower limit of minus infinity is a mathematical convenience it implies that to calculate the stress at time t, in the most general case, one must know the strain history infinitely far into the past, i.e., at all times t prior to time t. In practice this is not necessary. In general, an experiment is started at some time (f = 0) when the material is in a stress-free state. In this case, t(0) = 0, and... 

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