220 copyrightc 2005 by ali ghalambor boyun guo 110

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Unformatted text preview: rotation and reciprocation reduces the strength of casing. Wear models such as Maurer Engineering’s “CWEAR4”, DEA-42 Project, can effectively predict the degree of wear to be expected in a casing string. The wear is estimated as the average percentage of the casing wall thickness wore away. 220 Copyright(c) 2005 by Ali Ghalambor & Boyun Guo 110 Consider 9 5/8” ppf, P110 casing with a predicted wear of 10% of the casing wall thickness. Worn by 5”, 19.5 ppf, H-90 drill pipe.(Tool joint OD=6.5”) Burst Strength: The API Barlow equation for burst strength is : 2 Yst Pb = for 10% wear, t’=0.9t D and Burst(Worn) = 9810 psi Burst(Unworn) = 10900 psi Difference = -10%, the burst strength is directly proportional to wear. Collapse Strength: The API procedure of r determining collapse strength involves D/t comparisons to determine the failure mode. As t’=t(1-wear %), the failure mode for collapse might be different for worn casing than it was for the same but unworn casing. For the example, the failure mode remains plas...
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