The Oil Pipeline "Spoolpiece" Problem

This paper describes experiments conducted to determine whether a high-frequency transponding sonar could replace existing mechanical procedures which involve the use of saturation diving for the measurement of the mating gap between a submarine oil well-head riser and the production pipeline. Whilst the use of sonar transponders is widespread in underwater distance measurement, particularly in submarine navigation systems, it was far from clear at the outset of this study whether the outline technical specification requiring an accuracy of 1 cm in 100 m could actually be met. Furthermore, although a high sonar frequency was indicated by the stated requirement on precision, the relative lack of published information with respect to sound propagation in real-sea conditions in the high hundreds of kilohertz, made the practical tests described in this account a necessity.