In wntmg a book of this nature that will have reasonably general application the authors are confronted at the outset with the problem that although theory remains much the same everywhere, constructional practices that affect the design of pipelines are prone to vary, being influenced by such factors as local traditions, climate and geology. Also, although official regulations and recommendations within the UK are now fairly uniform, such requirements vary from country to country, and indeed can vary considerably within a single country. Also the extent to which the design engineer is free to make his own decisions and choice varies. Relative labour costs, availability of sophisticated plant and equipment and standards of workmanship exert powerful influences. Inevitably the book is directed in the first instance to practice within the UK, but where occasions arise throughout the text attention is drawn to variations that may arise elsewhere. In making comparisons between different practices it is of importance to consider the overall design. for instance in some countries it is customary to design for loadings that are average rather than maxima and to employ a relatively high overall design factor of safety to take care of contingencies, whereas in others, such as the UK, the reverse is the case.