m 



characteristics. For example, in Cook Inlet, Alaska, where 30-foot tides cause 

 surface currents of 13 feet per second and bottom currents of 6 feet per second, 

 and where severe weather conditions limit the laying season, the cost of an 

 8-inch line in 120 feet (37 meters) of water is approximately six times what it 

 is in the Gulf of Mexico." 



1. Weather. — The largest lay barges cannot operate in wave heights exceeding 

 10 to 15 feet and they experience difficulty transferring pipe in wave heights 

 less than this.^^ Thus, as operations expand into deeper, more exposed locations, 

 delays due to weather will increase and costs will rise. 



2. Location. — As pipelines are laid in more remote locations and further from 

 shore, mobilization and transportation expenses will increase. For example, a 

 lay barge and its support equipment may cost $20,000 per day in the Gulf of 

 Mexico and $60,000 per day in Cook Inlet." 



3. Method of Pipe Laying. — In water depths of less than 100 feet (30 meters), 

 most sizes of pipe are self-supporting and can be laid without the need of elab- 

 orate guides or tensioning systems to decrease the curvature. Stingers have 

 been used in water depths of up to 300 feet (91 meters) to guide the pipe from 

 the lay barge to the bottom. However, in this water depth a 700-foot stinger is 

 required, which is costly and cumbersome, and operations are plagued with 

 continued damage or trouble with the stinger." 



To eliminate the need for a long stinger, tensioning devices are used in con- 

 junction with small stingers in water depths greater than 250 feet (76 meters) 

 and up to 600 feet (183 meters)." The tension required to maintain minimum 

 curvature increases with size, and thus only small diameter pipelines can be 

 laid with this method in water depths from approximately 600 to 1,000 feet 

 (183 to 305 meters)." Beyond this depth new techniques will have to be 

 employed.^ 



4. Pipeline Burying. — In deep water, wave action is not as .strongly felt on 

 the bottom, and in areas where currents are not a problem, pipelines will not 

 have to be buried. Since most operators are currently burying pipelines in water 

 depths less than lOO to 200 feet (30 to 61 meters), the elimination of the need 

 to bury will partially offset the trends discussed above.*^ 



" M. E. Spaght, loc. cit. 



15 "Offshore Pipelining," loc. cit. 



18 Ibid. 



1' J. R. Dozier, loc. cit. 



1' H. M. Wilkinson and J. P. Fraser, "Deep Water Pipeline," Paper (API Division of 

 Production). 



" "Offshore Pipelining," loc. cit. 



"> J. Delarvell, "The French Install Submarine Pipeline at Depth of 1080 Ft.," Oil and 

 Gas Journal, August 7, 1967. 



21 R. Blumber, "Hurricane Winds, Waves and Currents Test Marine Pipe Line Design," 

 Pipe Line Industry (June-November 1964). 



"Offshore Pipelining." loc. cit. 



