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Drill-pipe and casing lengths and threads
10 February 2019
Good morning

I have got two questions  that I want to share with you and discuss the answer:

 1- why the Drillpipes and Casing have not the same length and we have many ranges and even for the same range we find different lengths?!

 2- why the drillstring is delivered with different threads and is not made from only one thread?!

Thanks

Dave
4 answer(s)
mhayes
Consultant Driling Engineer / ERD Advisor
Stanfield-Hayes Consulting
Total Posts: 39
Join Date: 25/03/11
Whilst History pays a part, it is still referenced in API standards and the length relates at least in part to rail car sizes and load capabilities. And though the preference will always be to make up minimum connections (i.e why Range 3 casing is the predominant length) some rigs are too small to drill with Range 3 or even 2 drillpipe due to limited height and kelly length but this is as much a commercial reason as a historic reason. Therefore the length is as much driven by history as the demands due to this historical constraint.

As far as threads are concerned, this is both historical and commercial, and based on general engineering requirements of the industry with different companies introducing new or different tooljoints to meet strength requirements, OD, drift, ease of make up, etc.
JDDrouin
Project Quality
SPREAD Associates
Total Posts: 105
Join Date: 06/05/09
Sidi,

The simple answer is "history".  A longer answer is that the oilfield is evolutionary in product development, and that there are a lot of twists and turns in the evolutionary bunny trail.

To explain the differences a bit more, in the early days of drilling and production, neither rig design nor the time to run tubulars were as 'engineered' as they are now, so there was not as tremendous an amount of importance placed on product development or standardization as there is now.  Further, there were also sound marketing tactics involved.  For example, going back to the mid- '70's, one of the tactics / philosophies adopted by several of the Japanese OCTG manufacturers when they were breaking into the US market, was to provide casing and tubing in lengths that varied by no more than a few inches ... it looked impressive and made product utilization much simpler, so was perceived as a higher quality product.

Further complicating the issue is that there were and still are some fairly cockamamie engineering / marketing concepts mixed in the industry as well (I could give you half-a-dozen or so clear, crystal clear examples, but don't need the lawsuits).

And, that's without getting into the various personalities of the personnel running the API Committees that set the specifications for API standard products.

Hope that helps a bit.
Augusto
Consultant [retired Shell staff]
SPREAD Associates
Total Posts: 252
Join Date: 02/09/05
The main difference is that the drillpipe is meant to be tripped in and out of the hole on a contnuous sequence.

Casing on the other end, is meant to be run in the hole, ONCE!

So the DP specs must respect the hoisting equipment for joint length i.e. there are rigs built for singles, for doubles, for trebbles and fourbles,

The Tool Joint coonections aim at having strengths equivalent  to the pipe bodies they are attached to, Torque resistance the main factor. So each component requires its optimum connection, obvious variable with the types: Drill Collars, Heavy Weight DP, Drill Pipe and even subs,

Casing joints aim solely at matched strength connections as toque transmission is a rare requirement, 

Often, the rig is built in a way to accept any type of string that the end user feels inclined to. Sometimes, availability is a powerful reason to use it.







DMEkas
Drlg Fluids Supv
SPREAD Associates
Total Posts: 9
Join Date: 26/03/10
Can't speak to casing, but tool joints are routinely manufactured longer than API spec to allow for recutting of threads when worn. Prevents having to by entire replacement pipe.
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