Abstract: Drill pipe damage primarily manifests as grooves and scratches on the joint shoulder, as well as corrosion and erosion of the pipe body. This article analyzes the causes of drill pipe damage and maintenance methods during drilling operations, aiming to provide guidance for drilling operations, extend the service life of drill pipe, and prevent drill pipe accidents.

I. Keywords: drill pipe; maintenance; use; prevention

The drill pipe is a crucial component of drilling machinery. The drill string, comprised of drill pipe, transmits torque and weight on bit, serves as a channel for drilling fluid, and is essential for drill bit replacement and accident handling. It is also the component most susceptible to damage.

II. Drill Pipe Forces and Operating Conditions

The drill string is an elastic system subjected to loads that vary in magnitude and direction during drilling. Loads borne by different parts of the drill string are unequal. Friction between the drill string and the hole wall, and occasional sticking, further complicate the stresses.

During the various drilling steps, the drill string experiences highly variable stress combinations due to various loads. The stresses acting within the drill string include tensile, compressive, torsional, and bending stresses.

The drill string, subject to constant bending and torsional deformation, experiences longitudinal and lateral vibrations. This vibration subjects the drill string and surface equipment to vibrational loads.

III. Drill Pipe Damage Conditions and Mechanism Analysis

According to the 2018 recycling inspection records of the Zhongyuan Project, drill rod sticking accounted for 66% of the total drill rod replacements; pipe bending accounted for 2.3% of the total drill rod replacements; arc-shaped grooves along the shoulder surface accounted for 35.2% of the total drill rod replacements; severe thread wear accounted for 13.2% of the total drill rod replacements; internal and external threads and joint shoulder defects accounted for 9.6% of the total drill rod replacements; internal and external thread shoulder punctures accounted for 5.7% of the total drill rod replacements; joint outer diameter eccentric wear and outer diameter less than the standard size accounted for 9.8% of the total drill rod replacements; pipe erosion, insufficient wall thickness or puncture leakage accounted for 17.6% of the total drill rod replacements. In response to the above-mentioned drill rod damage, a follow-up analysis and research on on-site drill rod damage was conducted, and it was found that the main aspects of drill rod damage are as follows:

(1) Causes of premature joint damage

  1. During the machining process, drill pipe joint threads fail to meet standards for pitch, finish, and surface hardness, causing galling.
  2. Thread compound is substandard and cannot adhere properly to the threads to form a protective film, leading to wear or galling under torque and compression.
  3. Inadequate cleaning of internal and external threads and shoulder surfaces, or insufficient or uneven application of thread compound, can cause abrasions and grooves on the joint shoulder, wear on the threads, shorten thread life, and even galling.
  4. Misalignment of internal and external threads during thread tightening can accelerate thread wear, lead to insufficient or excessive tightening torque, and breakage of external threads or expansion of internal threads into a flared shape.

(2) The outer diameter of the joint is worn or eccentrically worn due to the friction between the drill pipe and the well wall or casing during drilling and drilling.

(3) Drilling fluid corrosion and high-pressure, high-speed fluid erosion of the pipe body cause overall wall thickness loss or punctures. Long-term storage of new drill pipe absorbs corrosive gases such as CO2, causing electrochemical pitting corrosion both inside and outside the pipe.

The statistical results generally align with those from numerous drill pipe puncture accidents in the Zhongyuan Project. This indicates that a puncture at the location where the thickened transition zone within the drill pipe disappears is the primary form of drill pipe puncture failure.

(4) Drill pipe damage caused by mechanical defects includes: pipe bending due to improper use, impact of the internal threaded shoulder of the joint with the tripping elevator, damage to the joint shoulder or bending of the pipe caused by collisions between the drill pipe and the drill platform, and various damage and bending during transportation.

IV. Drill Pipe Maintenance and Use

(I) Maintenance and Use of Drill Pipe Threads and Joints

1. Protection During Field Use

1) Clean the drill pipe threads thoroughly before drilling, and apply a thread protector before the drill pipe is placed on the drill platform.

2) Use high-quality, standard drill pipe thread compound. 3) Before entering a rathole, drill pipe grease must be evenly applied to both internal and external threads (including the shoulder surface). When raising a single piece to the wellhead, drill pipe grease must be applied to the external threads a second time.

4) When connecting a single piece of kelly from a rathole, due to the angle with the rod axis, if the threads are not properly engaged, do not force them in. Connecting and disconnecting the drill pipe must be performed smoothly, ensuring that the thread does not press, pop, or hit the internal thread shoulder surface of the drill pipe. After fully tightening, tighten to the torque specified in API RP7G.

2. Protecting Drill Pipe Joints with Welded Hardbanding

Welded hardbanding technology can improve the wear resistance of drill pipe couplings, reduce eccentric wear of the drill pipe joint, and reduce wear on casing, especially technical casing. Statistics show that the average wear of drill pipe joint diameter per 10,000 meters of footage is reduced from 0.66 mm without welded hardbanding to 0.42 mm with welded hardbanding, increasing the service life of the drill pipe joint by 54.8%. (II) Maintenance and Use of Drill Pipe

1. Protection During Field Use

1) Drill pipe should be carefully inspected before use. Damaged, bent, or severely worn (over 1.5mm) drill pipe must not be used. Bent drill pipe can be reused after straightening. Straightened drill pipe is more susceptible to bending in the straightened area than before.

2) Avoid heavy hammering during use. The well stand should be padded with wooden planks to protect the threads. Proper stand supports and intermediate supports should be provided based on the stand length to prevent stand bending.

3) Design the drill pipe structure according to the drilling process and strictly adhere to the design technical parameters. Avoid pressurizing the drill pipe to minimize damage caused by pressure bending.

4) When transporting drill pipe, apply thread oil to the threads and then apply a thread protector. During loading and unloading, be careful not to drop the drill pipe to avoid denting it.

5) Establish a reasonable flaw detection cycle. Timely flaw detection inspections can effectively reduce and prevent drill pipe puncture and breakage accidents. 2. Use internal coating technology to protect the drill pipe body.

The internal coating forms a protective layer on the inner wall of the drill pipe, offering excellent resistance to erosion, acid and alkali, and high temperatures, as well as excellent wear resistance and drag reduction.

V. Conclusions and Recommendations

Through a comprehensive analysis of the modes and causes of drill pipe failure, combined with my years of work experience and relevant technical documentation, I propose the following preventive measures:

(I) Strengthen pre-entry inspection of drill pipe to ensure its quality. Pre-entry inspection of drill pipe primarily includes three aspects:

 

  1. Inspection of drill pipe quality upon delivery (material, hardness, threads, body, and heat treatment).

 

  1. Repair, inspection, sorting, and classification of recovered and stored drill pipe. The processing of stress grooves in threaded joints and the use of high-torsion double-shouldered drill pipe can effectively improve stress distribution within threaded joints, increase the load-bearing capacity of the threaded connection, reduce fatigue failure, and increase the fatigue life of the threaded connection. In complex well drilling operations, using double-shouldered drill pipe can effectively improve its load-bearing capacity, reduce drill pipe breakage and failure incidents, and enhance its safety and reliability.

 

  1. Drill crew technicians must conduct a detailed inspection and record the drill pipe before entering the well.

 

(II) Standardized Drill Pipe Operating Procedures:

  1. During make-up, evenly apply clean, standard thread compound to ensure a tight seal.

Excessively low tightening torque can cause the joint to vibrate, grinding the threads and sharpening them.

Thread damage caused by a lack of thread compound.

  1. Control the make-up torque and make the joint according to the specified optimal make-up torque value. Use a torque meter in good working order.

Excessively low tightening torque can cause the shoulder surface to not be tightened.

causing fatigue fracture of the male connector.

  1. Avoid surface damage to the drill pipe during operation, especially bruising of the drill pipe sealing surface and tong bite on the drill pipe body. If this occurs, the drill pipe must not be entered into the well. 4. The user should regularly check the weight gauge and weight recorder for proper operation to avoid being unable to properly analyze an accident.

 

  1. Avoid all improper operations to prevent damage to the drill pipe.

 

Failure caused by the male connector impacting the female connector’s shoulder.

 

Drill pipe damage caused by brake failure.

 

The following figure shows drill pipe damage caused by drill slip.

 

(III) Scientific and rational use of drill pipe:

 

  1. When assembling drill pipe, fully consider the smooth transition of the overall stiffness of the drill string, avoid sudden stiffness changes, and use weighted drill pipe. (Some well crews do not follow the design, change the drill pipe assembly, or fail to use weighted drill pipe.)

 

  1. Use larger drill pipe whenever possible to improve drill pipe stress and effectively increase the ability to handle drill pipe accidents.

 

  1. Rational selection of drilling parameters: The rotational speed should avoid drill string bouncing and drill string resonance. The weight on bit should be adjusted to avoid drill pipe buckling and eccentric wear caused by pressure.

 

Tensile damage caused by excessive torque. 4. Pay attention to pump pressure changes to promptly detect drill pipe leaks and reduce drill pipe breakage incidents. If a drill pipe failure occurs, contact our company promptly so we can collect firsthand, factual information.

 

  1. Regularly rotate the drill pipe’s position in the drill string to improve the stress conditions on the drill pipe.

 

  1. Maintain the pH value of the drilling fluid at around 9.0.

 

  1. When lowering the drill pipe from the rig floor, lower it steadily and do not slide it directly up and down. Drill pipe on site should not be stored on the floor. If stored for an extended period, apply thread protector oil.

 

  1. When tightening a new drill pipe for the first time and during the first few trips, tighten and grind it slowly according to the specified tightening torque to improve its wear resistance.

 

  1. Avoid forced tightening when threads are not properly aligned. This can damage the threads and shoulder surface, such as by using inappropriate thread and thread oil.

 

  1. Thread protectors should be used when moving drill pipe up and down the rig floor.

 

(IV) Strengthen routine maintenance and care of drill pipe:

 

  1. Maintain and care for the threaded area of the drill pipe joint. During storage, apply thread protector oil, and remove the rubber pads from the joints of the drill pipe stored for long periods.

 

  1. Clean the inner and outer surfaces of the drill pipe with mud to reduce chemical and oxygen corrosion.

 

  1. Strengthen flaw detection and inspection of the thickened transition zone of the drill pipe, which is prone to failure, to promptly detect crack initiation. Drill pipe used in a certain number of wells should undergo graded inspections (thickness measurement, magnetic flux leakage testing, etc.), and improve the internal coating of the drill pipe.

Conclusion

Drill pipe failures are largely preventable through strict quality inspections, proper handling, and adherence to maintenance protocols. Common issues like thread damage, wear, corrosion, and mechanical deformation can be minimized by applying protective coatings, using correct make-up torque, and rotating pipe positions regularly. A scientific approach to drilling parameters, along with routine flaw detection and timely repairs, is key to ensuring operational safety and extending the service life of drill pipes.