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Bending Strength Ratios

Posted by: Ben Grassham , E-mail: Address, on July 31, 2007 at 03:17 :

I've always been curious as to the nature of determining a bending strength ratio as stipulated in T.H.Hill specification in relation to Drill Collars and other BHA components. Following the instruction read in the DS-1 inspection guide a BSR is calculated with use of the measurement of ID at the pin connection and OD at the Box connection. Now to my way of thinking, it would be far more relevant to take this measurement from the ID of the engaged pin and the OD of the engaged box, as when made up these two connections become an integral section and the typical stress areas (last threads near pin shoulder and furthest thread from box shoulder) would be in direct relation to the dimensional characteristics of each - after all the the two ends when made up form an integral structure and fatigue failure will generally result from a weakness that generates from the combined section (even though one may exhibit the the contributing characteristic, the made up section will be bearing the bending stresses as a unit). Any thoughts or comments would be appreciated

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