Buoyancy analysis for concrete coating and weight spacing are two common methods used in pipeline construction to control buoyancy in water environments.
Buoyancy analysis and Concrete Coating Requirements –
This application is for the design of new pipe where the concrete coating is applied around each joint of pipe except for the cut back areas around the girth welds. These areas could be left open with corrosion coating or fitted with for concrete or other coating for mechanical protection to make up height difference if is used for an offshore using lay barge. It can be done either in plant for offshore or on the job site onshore manually by using forms around the pipe and having concrete trucks fill the area between the forms and corrosion coating.

Buoyancy Analysis and Concrete Weight Spacing –
This application is usually done onshore where there are wet land areas such a swamp, wetlands, etc. These calculations are set up for the separate weights, spaced at specific distances to keep the pipeline from floating to the surface. Example is a bolt on concrete weight as shown in the photo below. There are companies that have these concrete weights designed for each pipe size with quick installation. Note the wood lathes to protection the corrosion coating.

Calculations
Buoyancy Force

๐น๐ต โ Buoyancy Force (lbf)
๐ท๐ โ Pipe outside diameter including coating (in)
๐พ๐ค โ Unit weight of fluid/water (lb/ft3)
Weight of Steel Pipe in the Air

๐๐ โ Weight of bare pipe in air (lbf)
๐ท๐๐ โ Pipe outside diameter (in)
๐ก โ Pipe wall thickness (in)
Weight of Pipe Coating in the Air

๐๐ โ Weight of coating in air (lbf)
๐พ๐ โ Unit weight of coating (lb/ft3)
Weight of Product in the Pipe

๐๐๐ โ Weight of product in pipe (lbf)
๐พ๐๐ โ Unit weight of product in pipe (lb/ft3)
Downward Force of the Pipe

Net Controlling Force

๐น๐๐๐ก โ Net controlling force (lbf)
๐๐น = Safety Factor
Downward Force of the Concrete Weight

๐๐ค๐ก โ Weight of concrete (ft3)
๐พ๐ค๐ก โ Unit weight of concrete (lb/ft3)
๐พ๐ค โ Unit weight of fluid/water (lb/ft3)
Concrete Weight Spacing

