Calculations based on impulse-momentum and strain-energy 

 considerations were made to determine the stress levels which may be 

 expected during the stop/start lowering procedure. Typical results are 

 shown in Figure 5. As suspected, there is definitely an upper limit on the 

 velocity from which a pipe-load combination can be stopped. The overall 

 impression of the stopping operation is that delicate and careful control will 

 have to be exercised over the entire sequence. While the potential damage 

 of too rapid deceleration is great, the problem is more in the area of a 

 system limitation rather than a serious design drawback. Assuming adequate 

 precautions are taken (which perhaps would be nothing more than having 

 competent operators), it is safe to assume that excessive stresses due to this 

 mode of loading can be avoided during the stopping operation. 



The oscillations of the surface vessel, particularly in the heave mode, 

 cause significant stresses in the pipe at the support point. This problem is 

 comparatively difficult to solve because of the nonlinear damping due to 

 drag forces on the oscillating load and added mass. A simplified solution 

 has been derived and a program written for the computer; the output is the 

 normalized amplitude of the maximum dynamic force. Axial forces per 

 foot of heave for various load conditions and wave periods are given in 

 Appendix B. 



Table 5. Design Parameters for 10-3/4-Inch OD Casing 

 (Source: Jones and Laughlin Catalog, Oil Country Pipe, 1968 edition, p.c-25) 



Pipe Grade 



Weight 

 (lb/ft) 



Pipe Tensile Strength 

 (kips) 



Joint Strength'' 

 (kips) 



P-110 



55.50 

 60.70 

 65.70 



1,754 

 1,922 

 2,088 



1,923 

 2,107 

 2,289 



V-150 



65.702 

 71.102 



2,847 

 3,094 



2,799 

 2,957 



^Joints same material as pipe; joints for P-1 10 pipe could be one grade 

 higher. 

 ^Casing is non-API; available on inquiry basis. 



20 



