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Tricone Bits Shelf Life.
31 January 2019
Due to the war in Yemen, the Drilling Operation was suspended in April 2015; as result of that,  we have a good amount of 17.1/2", 12.1/4", 8.1/2" and 6" tricone bits (major brands) in the warehouse, most of them were purchased between 2010 and 2015. I am looking for comments and recommendations regarding the use of these bits exceeding the published manufacture's shelf life. I am aware of the potential risks published by manufactures, however, I would like to have experience based comments and recommendations from the community.
Most of these bits were the latest generation at the time with features to drill tough and abrasive formations 
4 answer(s)
Project Quality
SPREAD Associates
Total Posts: 105
Join Date: 06/05/09

Technically, as long as those bits were stored in a warehouse, presumably in their original boxes, they have (more or less), an indefinite shelf life.  Consider this, they were designed for use in an infinitely harsher environment ... even storage in a non-air conditioned warehouse doesn't even come close to the environment or operating conditions they were designed for use in.

However, in reality this boils down a perception issue ... if one of those bits 'fails' (under any definition of that term), "blame" will automatically be placed on using "old bits", prior to any investigation, without a scintilla of actual empirical evidence to back up that assertion.  And that means that the judgement of the individual(s) who sanctioned their use WILL be questioned.  A serious headache at the least.

Ref the use of cosmoline or any other lubricant, I recommend you think long and hard about that.  The clearance between the cone and the shank is deliberately kept as small as possible in order to keep cuttings from being able to damage the o-ring during use (there is at least one more reason, but it's not relevant to this issue).  So, unless the treatment is 'forced' into that gap, it's not going to contact the o-ring but may become the perfect material to entrap fines that might damage the seal surface the o-ring contacts.

As an FYI, assuming warehouse storage, there are really only three failure modes possible on unused, sealed bearing roller cone bits; the grease may de-emulsify or the grease cartridge assembly may fail, thus rendering the grease only partially effective, or the o-rings may become brittle and fail.

On the grease issue, I know of no research released by the bit manufacturers that show "X" amount of life for their bearing grease or cartridge assembly (and I would guess that that issue has been performed, but would not be made publicly available).  On o-rings, I do know of non-oilfield research that shows nitrile o-rings (the type used in bits) being perfectly competent after decades.  That's not to say they have an infinite life, just that it's a very long time when it's in a static situation.

Hope that helps,

senior operations engineer
SPREAD Associates
Total Posts: 2
Join Date: 17/08/17
Hi Mr. Fernando,
As I have known, they are tri-cone bits, the risk will be in the bearing seal for he movable parts (cone). there are a lot of improvements in technology (Hughes, Smith, etc.) but still we have risks. Cosmoline is good option but you have some issues now, # it is expensive compared with Tri-cone bits and # it is too late because they have been already exposed to the erosion. Most of the manufacturers can guarantee till 4 years but we have some hidden safety margins in our pockets. So, my recommendation is to use it but with higher safety margins, we have some details about the bit size, version, bearing technology but generally, I recommend in two directions; to consider them as used ones with 50 -70% bit life. That means no tough drilling conditions, no long drilling phase as would be recommended before. That is the managerial recommendation. The other direction is the practical / field / rig floor recommendation; take extra care while application or drilling, listen closely to the downhole signs and do not drop the silly signs as we used to drop in the normal conditions, because it might cost much more than the bit price. It is tri-cone so it is no expensive but fishing job is an expensive and time consuming. I can share with you some field hints for bit application. Please do not forget the per-job field test with reduced flow. Good luck
SPREAD Associates
Total Posts: 132
Join Date: 05/03/08
Hello Fernando,

I would approach the manufacturers themselves and see what they say.

Of course, they have the potential to be a little biased, in that they also want to sell you a new product!

However, you could also ask some of the independent bit specialists that are around (Aurora in ABZ is one that springs to mind).

The rule of thumb used to be that they wouldn't recommend running any rock bit that was more than 3 years old, as you don't know what has happened to the seals, or the bearings could have developed small 'flat spots' if they have been stored upright for that period of time.

However, that was from several years ago and the recommendation may have changed since then.

I would be very wary about running any of these, given that they are at least four years old.

It only takes one to loose a cone prematurely to offset the savings made in not bringing in new ones.

In addition, advances in seal, bearing and cutter technology over the last few years may have made them obsolete in any case.

Best Regards

SPREAD Associates
Total Posts: 2
Join Date: 06/02/18
Were it me--I would try to put them in a preservative such as Cosmoline. Below is the generic description of it. They would outlast our lifetime then.

Cosmoline is the genericized trademark for a common class of brown wax-like petroleum-based rust inhibitors, typically conforming to United States Military Standard MIL-C-11796C Class 3. They are viscous when freshly applied, have a slight fluorescence, and solidify over time and exposure to air.
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