Can someone explain to me how the tapered threads on drill pipe work? I've seen different shows on TV that are about Drilling Rigs. I'm wondering how they can thread together thousands of feet of pipe 30' or 60' at a time and keep the threads together. I know they turn only in one direction but it seems like the torque would build up and then spin it apart at some point.
How so? Just gets tighter. Been working real well for at least 90 years.
Bigger stuff (not drill pipe) requires hydraulic "makeup/breakout" machines to put them together and take them apart.
Yep, they will break loose if turned to the left. Any driller that even thinks of backing off the drill string to the left would be run off location in a heart beat!!!
The make up torque to tighten the connections is so high that it relies on frictional contact with drill pipe dope provides a "bite" to keep them tighten. This make-up torque may be as high as 15,000 ft/lbs of torque, or less/greater, depending on size and type of connections used. And amazing they stay connected and torqued up to spec. Most of the time, it takes more torque to break loose than to make-up. The steep taper thread allows the pin and box connection to align up and the two threads to start without cross threading, and also fast to connect and disconnect.
So how many turns does it take to make up the connection to the point where it is starting to be tight?
Wouldn't think it was many, seems like the taper means they won't even engage until only a couple threads apart.
About 6-10 turns to "hand tight", then about 1/4 to 1/2 turn to full torque make-up.
Last summer the wife and I went to Alaska and visited, among other spots, Prudhoe Bay. I spotted a machine shop and got a look around. Pictures are at
http://neme-.org/Alaska/Alaska_Page_15.htm including a close up of a drill pipe thread in the lathe.
I understand for a thread form to bve approved by the API it has to sold and used to demonstrate that it works and does not break stick etc. then it can get API stamp of approval.
There are dozens if not hundreds of different thread forms used in the oilfield. Drilco, now Smith International used to publish a spec book with all the thread forms in use.
Drillers didn't used to trust a thread cut on a manual lathe because the taper and form is so critical. They preferred hobbed threads expecting them to be truer to the true shape. Hobbing threads being a milling operation also left minute scallops in the surface that held the thread lubricant better. When NC lathes became common they pretty much took over the threading from the hobs.
Warner & Swasey built some 4-A's, SC-28's and SC-36's with thread hobs on the turret but all of the users eventually removed the hobs after a single point cut thread became acceptable.
Watched an old feller cutting drill pipe threads and remarked about how effortlessly he did it. He said when he graduated from technical school years ago,his teacher recomended that he apply to a machine shop where they did a lot of threading.He said it only took him seven years to be able to make up a good drill stem.
Used to work for Drilco - still have the fat little book [img]smile.gif[/img]
Not all down-hole connections are tapered thread. One of the more difficult threads to counterfeit is the CS Hydril. Until the early 80's they had to be purchased from Hydril to have any assurance of proper performance. This thread consists of two modified buttress threads of different diameters. They are cut in phase with each other. there is a torque shoulder between them. Both threads are higbyed. The higbys and pull-outs are in line. The front of the pin has a double taper. At the rear of the pin is an angular undercut. The box also has double threads and the torque shoulder between. The rear of the box has a single angle that receives the intersection of the double tapers on the front of the pin. The front of the box has an externally tapered lip that locks under the undercut at the rear of the pin.
The connection is difficult to gage. Most connections having tapered threads are checked for standoff between box and pin. This does not tell the whole story with the CS Hydril. It torques up at the shoulders in between the large and small threads. Further torque stretches the outer end of the box and pin until they make up against corresponding surfaces.
Back in 1980 I got caught counterfeiting this "proprietary" thread. Until then Hydril didn't worry about it because it was considered impossible to do it on a lathe so that the connections would pass a hydrostat. I figured how to do it on a Mazak Powermaster. No hob needed any more. Along comes the friendly Mazak rep with a guy from Hydril who says all will be forgiven if I just show how I did it. Next thing I know, my boss complains that Mazak has sold lathes to Hydril so they can try cutting their connections the easy way. Fortunately, he was pretty much out of the pipe business and doing fishing tools, shock subs and jars. I left the oil patch shortly after and lost touch with that world. I wonder if any of you can tell me if Hydril now does their connections with a lathe or did they stick with hobbing?
If you have a further interest in drill pipe threads, there's a book/booklet called, "What keeps your string together." The one I saw had the thread specs and drawings for a bunch of different drill stem threads.
Warner & Swasey sold Hydril a batch of CNC lathes probably in the middle 1970's to cut that thread. They had to hop up the X and U axis to get out of the cut fast at the end of the thread because they only allowed about a 1/4 of a turn of incomplete thread at the end. I was later after 1984 involved in fixing up several of those lathes to go to Venezuala. They also had a building full of Cincinnati CNC's to cut that thread. Each Hydril lathe operator had a whole table full of gages to check those threads.
Well, at the time, back in the 50s and 60s, I knew very litle about the business end of a lathe, much less how to cut these complex thread forms.
But,I did spend some time at the business end of "throwing the chain" and "bucking the tongs", both in West Texas and South Louisiana. Rough life and I doubt I'd have enough fingers to type, if I was still living,to type this postif I had stayed in that game.
Yall, I'll say it now, the guys on those rigs are one tough bunch.
Well , for what is's worth, I just made three power head drive shafts (tubular)for a local water well driller. These are of course smaller than oil well rigs but it still employs the same principles as far as the tapered threads are concerned.
These threads are modified 4 TPI on a 2"/ft. taper ( included ). There is a shoulder that the mating part has to screw up to at which time the threads should be tight as well. This thread form is called MayHew jr. (Google MayHew jr.)
This was done on an old Hendy lathe that has a quick retracting cross slide in conjunction with a taper attachment. It still made for a tight sphnicter until I made a 16" handle for the quick retracter and gained a little consistence in retracting the tool. A quarter of a turn is about right for the incomplete thread.
this is interesting. I didn't think very many people knew about this little niche of the machining world. I worked in a oil field machine shop in Farmington, NM for a year and learned ALOT about threading. cost is no object when those roughnecks need something in the field. they don't F**k around. Working in that enviroment gives new meaning to "needed yesterday."
" I wonder if any of you can tell me if Hydril now does their connections with a lathe or did they stick with hobbing? "
I don't know about that but all our connections were done single point.
We all our threading on an old hydrotrol, a dean smith and grace, both with air kick out and a 1995 Mazak M5. A good journeyman could do about 8-10 drill collars a night on the manual machines and about 18-25 on the M5.
hello all ,i am a supervisor for drilco,(well now called smith services drilco group by some) came from morgan city louisianna,,and am now located in broussard louisianna.around laffayette.we use v bottom inserts to thread with. on 12" hollow spindle lehmanns.3 of them. air kick out and rapid traverse.we also have a mazak slant turn 450,mostly used to cut drill pipe,as drill pipe comes in larger quanitys than collars and heavy wate.if you have any questions on collars,pipe subs,etc, let me know .as for the hobb last one we used in mrgan city was about 83 or 4 the collar shop there was shut down and moved to laffayette,the pipe shop stayed a while,longer and are now located at port fourchon louisianna..we have been single point threading on lehmanns ever since.we have had the mazak,about 3 or 4 years now. hence the name mazak,sure was glad to see that machine as we were cutting pipe and collars,repair manufacture,turning build up joints prepping stub collars etc,and that machine lightened the load of cutting drill pipe as well.we for a time were the collar shop and the pipe shop. in a sense the lehmanns are the collar shop now and the mazak is the pipe shop.johnoder ,the drilco hand is still around.if i might ask,what did you do at drilco? i assume in houston? its great to meet you,as it seems not many have heard of drilco,much less have worked there. i train poeple,for the machine shop here and they know drilco,and only a few get the name drilco hand.
Working for Warner & Swasey I installed the very first SC-32 NC lath in the Drilco plant in Houston. The maing building was still under construction, we started it up in the smaller building on the north side of the main building which was finished first. Drilco's NC programmer Richard Wong and I spent a week in Cleveland before that checking out the machine. Had freezing rain for a week. Richard always waited in the motel while I chipped our way into the rental car. Richard is a great guy and
Have you ever met a guy named Terry Maness up in Farmington?
He worked the oil patches a tool pusher unitl he went into sales for FMC, and Stinger Wellhead.
Just thought I'd ask, since it is a small town and all.