This chapter presents design and construction information on providing buoyancy control for overland pipelines. Pipelines are subject to natural positive buoyancy when placed below the water table. The magnitude of the buoyant effect is proportional to the pipeline diameter. The need to mitigate the pipe buoyancy depends on many factors. These factors include the pipeline material, the pipe diameter and its wall thickness, the pipe coating, the pipe product, the time of installation, and the density and type of trench backfill soil or imported material. Even pipelines carrying a heavy product may require the use of buoyancy control measures as they could be subject to excessive upward buoyancy forces in the period between pipe installation and full operation. All factors should be taken into account when determining the optimum type and frequency of buoyancy control measures.
Buoyancy control is rarely a pipe integrity issue. The floating of a pipe to the ground surface can relieve pipe stress rather than add to it. However, pipe exposure can result in costly repairs to rebury the pipe, and can expose the pipe to other dangers, such as third party damage or damage from debris carried by fast flowing watercourses. Thus, it is usually desirable to maintain a minimum soil cover over cross-country pipelines.
