There is some question whether the standard oil field drill pipe 

 coupling will perform successfully in a heavy-lift operation. Drill pipes are, 

 of course, rotated during the drilling operation and this helps prevent the 

 couplings from unscrewing. It is conceivable that some unexpected vibrations 

 in the drill string would tend to loosen the connections if a load were simply 

 hung on the pipe. While this has not been given any thoughtful attention, it 

 appears to be at worst a minor problem which could be solved by incorporating 

 a mechanical locking device into the coupling. 



PIPE STRING DESIGN 



Assuming a safety factor of two and limiting attention to the severest 

 case of a 600-ton load at 6,000 feet, it can be seen that of the different pipes 

 given in Table 4, only the last three of V-1 50 grade steel will meet the 

 requirements. These are the pipes of 10-3/4-inch OD weighing 71.1, 76.0, 

 or 81 .0 pounds per foot. The 10-3/4-inch OD pipe weighing 65.7 pounds 

 per foot almost meets the design criteria, having a safety factor of 1 .93. The 

 9-5/8-inch OD pipe weighing 61.1 pounds per foot has a safety factor of 

 1 .81 . The safety factors are presented in Table B-1 . 





Table B-1. 



Safety Factors for Pipe 



Grade 



OD 

 (in.) 



Weight 

 (lb/ft in air) 



Safety Factor 



for 600 Tons at 



6,000 Feet 



P-110 



9-5/8 



53.5 



1.22 





10-3/4 



65.7 



1.47 





10-3/4 



71.1 



1.55 





10-3/4 



76.0 



1.62 





10-3/4 



81.0 



1.72 



V-1 50 



9-5/8 



53.5 



1.64 





9-5/8 



58.4 



1.75 





9-5/8 



61.1 



1.81 





10-3/4 



65.7 



1.93 





10-3/4 



71.1 



2.05 





10-3/4 



76.0 



2.17 





10-3/4 



81.0 



2.17 



105 



