Hi Regis,

The OD tolerance is dependant on bit type and size.

Basically the OD tolerance for Rock Bits is 0, +ve while for PDC & Diamond bits, it's -ve, 0.

http://www.rock-drill-bit.com/api-standards.html

All the best

Scott

Hi Hideaki

To my knowledge bit OD manufacturing tolerance has alway been [+0, -1/32in].
Opened to see this postulate challenged though.

Régis

Hide-san,

Just saying, be pragmatic for the purpose.

To accept what was purchased, drift as per that agreed in the purchase agreement specifications.

Most importantly, prior to use, going in the hole, drift for the maximum i.d. needed for the anticipated tools one will be running in that casing or tubing, and record that.

In all cases, physically measure the drift to make absolutely sure the drift mandrel is the actual diameter and length you need it to be, prior to use. If it's a lot of casing or tubing to drift, check the drift measurements mid-job.

Kind regards,
Allan

I believe we are not giving the due importance to the connection chosen but MAINLY how the pin thread is cut.
If the threading machine is index on the OD of the pipe, you are bound to have more problems than if you index the lathe on the ID of the pipe. There is a publication by Nippon Steel, based on data coming from Oman.
People forget that the Wall thickness of the casing is not uniform meaning that the ID is NOT concentric with OD!

Anyhow the special drift attraction is the extra length of the drift mandrel. Because of that should always be spacified.

Thank you everyone !!

The other issues with any drift has always been the OD. Was it originally manufactured to the correct OD and within the tolerance specification. Without checking I think the tolerance was plus 0.005”.
Do you have a certificate?
is the drift serial numbered ?

Hide-San,

I agree with the other posters that you have to ensure that the casing specs and drift criteria are agreed with the manufacturer (or stockist) upfront.

For 9 5/8" 53.5 lb/ft casing, in my experience it has always been ordered as special / alternative drift to 8.500".

We then used an 8.500" drift on the casing which was at least 12" long to meet API specs, although if the drift was having to be manufactured from scratch, I usually specify 24".

The reason for not taking into account the OD tolerance of a rock bit, was that there was sufficient 'give' in the bearing pack that the bit would pass through 8.500" without damage (had many discussions with bit manufacturers about this back then).

Back in the 80's and 90's, ID tolerance was always a concern for this OD/weight combination (also for 13 3/8" 72 lb/ft) and drift failures were not uncommon.

But I've been assured by Operator casing specialists in the last few years that the casing manufacturing process has been improved to the extent that even if you don't actually order the 53.5 lb/ft as 'special/alternative drift', it should still pass an 8.500" OD drift because the mill will use as little steel as possible to maximise their profit.

Having said that, I've not been brave enough to NOT include the 'alternative drift' phrase when ordering!

Oh, and to answer your original question, I don't recall ever using a drift that did take into account the OD tolerance of a rock bit.

Have you talked with your bit provider(s) about the 'give' in their bearing packs, as these days it might not be the case?

All the best

Scott

Hi all,

Good input from Allan.

You have to specify what you require. If you will drill an 8.500" hole section after running 9.5/8"-53.50# weight casing. You want to have casing ordered/allocated which suits this requirement, i.e. 8.500" SD spec pipe.

As mentioned by Dave as well the length of the drift mandrel can vary. With Shell the requirement in the quality plan was; 12" long mandrels are used for casing sizes, 6" for liners and 42" for tubing. That is deviating a bit from the API standard. Meaning if you want to get, e.g., 5" tubing drifted with a 42" long mandrel, it will have to be agreed in a quality plan or shall be clear as a requirement on the purchase order send to the manufacturer/supplier. 

In addition can only recommend, sure you do, is to have all equipment properly measured before running. E.g. make it mandatory that the bit supplier also puts a ring gauge over the bit prior sending it out to your rig. But again, would still get someone accountable on the rig to measure it prior running.

Best regards,

Marcel de Klerk

Dear Hide-san,

One drifts the casing for whatever purpose drives the drift i.d. requirement. A lot of operators use 9 5/8" 53.5 # casing and drill 8.5" hole afterward. API drift for that casing is 8.379" therefore requiring a special drift larger than API specified for that casing.

As Dave-san mentioned, a specific drift length is also part of the drift dimension criteria. Here is a link to an article I just grabbed off a Google search; Microsoft Word - drift-005 (hunting-intl.com)

Also note their reference, "The latest edition of the following documents shall form part of this specification: 2.1.1 API Specification 5CT 2.1.2 API RP5A5"

One should also take note that drifts wear down after a lot of use therefore the drift dimensions must be checked prior to use, to ensure they are what they need to be.

Kind regards,
Allan

Thank you for your comment.

Dear Hide-san

I'm sorry that no-one has yet responded to your discussion.

I do recall, when working for Shell UK in the 80s, that we would often go for the special drift.  From memory, not all the joints passed this criterion, because we not only specified the OD of the drift but also its length.

I hope that other members, who have a fresher memory than me, will contribute to this thread.

Kind regards

Dave