Failure Modes of Tri-cone Bits

Table of Contents

Tri-cone bits, recognized for their efficiency and durability, have found widespread application in fields such as oil, natural gas, and other resource extraction industries. However, in actual use, tri-cone bits may suffer from various failure modes due to the influence of various factors. This article will give you a detailed introduction to the failure modes of tri-cone bits to help you better understand and prevent the occurrence of these failure modes.

Tricone Bit

The common failure modes of mining tri-cone bits include bearing failure, cutting structure failure, cone shell wear, and gauge structure damage.

Bearing failure

During the operation of the drill bit, the bearing generates axial and radial forces. The axial force is borne by the thrust block and the second stop surface, while the radial force is supported by the large and small rollers. Under normal conditions, the steel ball has no force. However, in formations where the drill bit is lifting and the hole is collapsed and returned to the drill, the steel ball will be stressed, which reduces the bearings’ service life. Hence, the drill operator is required to rotate the drill pipe while lifting the drill bit to minimize the force exerted on the steel ball.

The service life of a rolling bearing: the total number of revolutions that the bearing and any part can run before fatigue pitting occurs, or the number of operating hours at a certain number of revolutions is called the bearing service life. The service life of rolling bearings is inversely proportional to the working pressure; the higher the working pressure, the lower the bearing service life.

Bearing failure is the main form of mining tri-cone bit failure. Common bearing failures are divided by failure location:

Radial failure

Excessive drilling pressure, fatigue peeling and wear of the bearing surface of the journal, and wear of the roller.

Axial failure

The thrust block is worn or broken, and the two stop surfaces are worn.

Seal failure

The wear of the palm tip causes contact wear between the seal ring and rock debris, the expansion of grease squeezes the seal ring, and the bearing is abnormally stressed and eccentrically loaded.

Cutting structure failure

The failure of the cutting structure is mainly the wear, chipping, and tooth loss of carbide. The specific failure forms are:

A row of broken teeth

The drill pipe rotates too high, and the linear velocity of a row of teeth is too high.

The tooth material is hard, the tooth shape is not suitable, and the tooth height is high.

The bending moment becomes bigger after the shell wears and the exposed height increases.

Broken teeth in the inner row

The drilling pressure is too high when the formation is hard.

There is a foreign object in the hole.

Tooth material is hard.

The tooth type is not suitable.

The tooth height is high.

Increase bending moment after shell wear.

The cone moves and fights.

Loss teeth

The interference amount of teeth and perforations are small.

Carbide pressure deviation.

The tooth hole roughness is poor.

Decrease in tooth fixing force after cone housing wear.

Worn carbide

Tooth material is soft.

The slag discharge is abnormal, and carbides are broken repeatedly.

The cone of the gears leads to flat grinding of carbide tops.

Shell wear and gauge structure damage

Abrasion of the cone shell and core out.

The formation is highly abrasive.

The stratum is soft, the selection is not suitable, carbides enter the stratum, or after breaking or dropping the tooth, the shell directly contacts the rock to participate in the crushing, resulting in the cone shell wear.

Abnormal slag discharge caused by air compressor air volume, insufficient air pressure or unsuitable nozzle, etc.

Abrasion of shirttail and backing.

The screw thread is biased upwards, resulting in eccentric wear of shirttail.

Abnormal slag discharge caused by insufficient air volume and air pressure of air compressor or improper nozzle, rock debris suspension leads to wear of shirttail and backing.

Abnormal slag discharge caused by inappropriate selection of drill pipe diameter.

The collapse of the hole and wear of shirttail group due to backward scratching of drill bit.

After use, most blunt drill bits have multiple failure modes at the same time, and it is difficult to determine the main form of failure and the early form of failure of a drill bit. Because failure in one part of the drill bit can cause failure in other parts. For example, bearing failure will lead to cones fighting, absenteeism, or jamming, which will lead to broken teeth or flat grinding of carbide, while bearing absenteeism will also make the cones lose the protection of the shirttail tip, which will also lead to the wear of the shirttail tip and backing. The broken teeth and wear of carbide will also cause uneven force on the gear and accelerate the failure of the bearing. The wear of shirttail tip will reduce the protection of the bearing sealing ring and accelerate the failure of the bearing.

For the above reasons, it is difficult to judge the failure mode of a blunt drill bit, especially on some foreign automatic drilling rigs, the use of the drill bit is relatively thorough, which often conceals the early failure mode of the drill bit. Therefore, in mine service, the following two points can be done to better find the early failure mode and major failure mode of the drill bit:

1. Check as many blunt drill bits as possible, and conduct a comparative analysis through the status of a large number of blunt drill bits.

2. Track the use process of drill bit, according to the average feed life of drill bit, gradually check, take photos, and record the state of the cutting structure, bearing, shirttail, and other parts in each stage.

To sum up, there are many failure modes of tri-cone bits. To prevent the occurrence of these failure modes, corresponding measures should be taken, such as selecting materials with good wear resistance, optimizing structural design, and strengthening lubrication and cooling. Moreover, regular inspection and maintenance of tri-cone bits are essential to promptly detect and address issues, ensuring their proper operation and optimal performance.

Conclusion

In practical applications, it’s crucial to select the appropriate tri-cone bit and corresponding preventive measures based on the specific situation. This approach aims to maximize its service life and work efficiency. At the same time, technological research and development and innovation should also be strengthened to continuously improve and perfect the design and manufacturing process of tri-cone bits to meet changing market demands and improve the overall level of the drilling industry. By employing sensible use and maintenance practices,  we can effectively extend the service life of the tri-cone bit, improve the efficiency and quality of drilling operations, and provide more reliable and efficient technical support for the extraction of oil, natural gas, and other resources.

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