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- since 1996 -
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Technical Discussions
Ben Grassham
Ben Grassham
03:17 Jul-31-2007
Bending Strength Ratios

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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Andreas Voge
NDT Inspector, Specially in the oilfield
Tuboscope Vetco(Deutschland)Gmbh, Germany, Joined Oct 1999, 130

Andreas Voge

NDT Inspector, Specially in the oilfield
Tuboscope Vetco(Deutschland)Gmbh,
Germany,
Joined Oct 1999
130
06:58 Aug-01-2007
Re: Bending Strength Ratios
----------- Start Original Message -----------
: 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
------------ End Original Message ------------
This connection is not intregral structure , this is the case of drillpipe connection , where the connection is stronger than the pipe and the tube is more flexible.
On drillcollar the body is stiffer than the body ,if you look at the cross section if drillcollar (sample 8" OD X 213/16"ID) give you app. 21/2" wall ,now look at the crossecttion of the connection it will be a lot smaller.
This calculation of BSR is descriped at API SPEC 7.

Andreas





 
 Reply 
 
Bruce McPherson
Bruce McPherson
07:48 Jan-16-2008
Re: Bending Strength Ratios
Ben,
You are quite correct, when 2 drill collars are made up, the BSR of the connection depends on the connection type, plus the box OD and pin ID of the made up connection.
Measuring the box OD and pin ID of a single collar and using those numbers to calculate BSR for that collar is theoretically incorrect.
However, in practice this method works for the following reasons:
Drill collar pin ID does not change significantly during service (whereas Box OD does)
BSR is much less sensitive to changes in pin ID than in Box OD (by about a factor of 2.5)
This means that minor changes in the ID's on a string of drill collars will not have much effect on the BSR.
When all the OD's and ID's in the drill collar string have been measured, it is good practice to make 2 further BSR calculations using a) The largest OD and largest ID - this will give the highest BSR
b) The smallest OD and the smallest ID - this will give the lowest BSR
If these highest and lowest BSR's are within the acceptance criteria, then you can be certain that whichever collars are made up together, the BSR for their conections will be acceptable
Hope this helps

Bruce McPherson


------ Start Original Message -----------
: 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
------------ End Original Message ------------




 
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khalid latif
khalid latif
06:53 Jan-09-2016
Re: Bending Strength Ratios
In Reply to Ben Grassham at 03:17 Jul-31-2007 (Opening).

how can find BSR of drill steem

 
 Reply 
 
Andreas
NDT Inspector, Specially in the oilfield
Tuboscope Vetco(Deutschland)Gmbh, Germany, Joined Oct 1999, 130

Andreas

NDT Inspector, Specially in the oilfield
Tuboscope Vetco(Deutschland)Gmbh,
Germany,
Joined Oct 1999
130
14:26 Jan-09-2016
Re: Bending Strength Ratios
In Reply to khalid latif at 06:53 Jan-09-2016 .

Look in the specification like DS-1 , NS-2 and API RP7G-2 you will find the formulas and lookup tables for different OD&ID's.

Regards

Andreas

 
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