(d) A 12 OD steel subsea export line is to be laid between two offshore production...

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(d) A 12" OD steel subsea export line is to be laid between two offshore production platforms. The seabed consists of gravel and sand. There are no physical obstructions on the pipelay route but there are strong currents, essentially oriented orthogonally to the pipeline route, which could cause scouring and instability. The pipeline is to be thermally insulated and laid directly on the seabed. SG seawater is 1.03 SG steel is 7.85 One cubic foot of fresh water (SG = 1.00) weighs 62.4 lb/cu ft. (i) Briefly describe the measures you would take to mitigate the risks of pipeline scour. (ii) For stability, the wall thickness must be enough to provide a net down force on the seabed of 80 lb/ft when the pipe is empty. Calculate the wall thickness (t) of the pipe. (c) A 24" OD steel pipeline, coated with a 3 1/2" thick layer of reinforced concrete, is laid empty on the seabed. The pipe wall thickness is 0.75". SG concrete, including reinforcement, is 2.8 SG seawater is 1.05 SG steel is 7.85. One cubic foot of fresh water (SG = 1.00) weighs 62.4 lb (i) Calculate the air weight of the steel pipe in lb/ft. (ii) Calculate the down force on the seabed in lb/ft when the pipe has been laid and filled with seawater for hydro testing. (d) A 12" OD steel subsea export line is to be laid between two offshore production platforms. The seabed consists of gravel and sand. There are no physical obstructions on the pipelay route but there are strong currents, essentially oriented orthogonally to the pipeline route, which could cause scouring and instability. The pipeline is to be thermally insulated and laid directly on the seabed. SG seawater is 1.03 SG steel is 7.85 One cubic foot of fresh water (SG = 1.00) weighs 62.4 lb/cu ft. (i) Briefly describe the measures you would take to mitigate the risks of pipeline scour. (ii) For stability, the wall thickness must be enough to provide a net down force on the seabed of 80 lb/ft when the pipe is empty. Calculate the wall thickness (t) of the pipe. (c) A 24" OD steel pipeline, coated with a 3 1/2" thick layer of reinforced concrete, is laid empty on the seabed. The pipe wall thickness is 0.75". SG concrete, including reinforcement, is 2.8 SG seawater is 1.05 SG steel is 7.85. One cubic foot of fresh water (SG = 1.00) weighs 62.4 lb (i) Calculate the air weight of the steel pipe in lb/ft. (ii) Calculate the down force on the seabed in lb/ft when the pipe has been laid and filled with seawater for hydro testing.