Introduction 'They don't make it the way they used to,' or words to that effect are often heard these days and invariably reflect sadness (or frustration) that the high standards of a bygone age are no longer applicable. The pipeline industry could perhaps use the same expression but the meaning would very different. The modern pipeline embodies a higher degree of technology and, in consequences, of safety, than ever before. A glance at a map showing major pipeline systems gives some idea of the degree to which industry is committed to transporting an ever-widening range of raw materials and products. There are, however, a number of facets to this growth pattern which are under regular review. Firstly, over the last 25 years standards have changed considerably. Pipelines built in this period have progressively taken advantage of the availability of new steels and new technology. Secondly, fatigue stresses leading to brittle and ductile fractures have been closely studied along with many other operational factors affecting pipeline integrity. Thirdly, the growing proximity of one pipeline service to another, in some cases involving use of a common wayleave, places a responsibility on each occupier with reference to the security of the other. Fourthly, increased speeds and density of road, rail and air travel present a potential hazard to buried services. Finally, expanding population and the decentralization of industry lessens the distance between major pipeline systems and populated areas. So to some extent there is a conflicting situation - pipelines are designed and built to a better standard than ever before but may be subject to a greater hazard than previously envisaged. The pipeline industry is very aware of the problems and this paper is intended to cover only one aspect, that of irregularities in pipeline diameter.