Precautions When Using Pup Joints of Different Specifications

Length specifications

1. Short-length pup joints (such as less than 1 meter)

a. Pay attention to the stability of the connection

Due to its short length, when connecting to equipment such as drill strings, special attention should be paid to the tightness and stability of the connection. For example, in oil drilling, it should be ensured that the threads at both ends of the pup joint are fully matched with the threads of adjacent components and the tightening torque meets the standard to prevent loosening during drilling. It is generally required that the tightening torque error be controlled within ±10% to ensure the reliability of the connection.

b. Prevent local stress concentration

Short-length pup joints may cause local stress concentration in the drill string. When using, its position should be considered to avoid placing it in the part where the drill string is bent or subjected to greater force. When designing the drill string assembly, mechanical analysis software should be used for simulation and calculation to ensure that the stress distribution at the location of the pup joint is uniform and avoid local stress exceeding the yield limit of the material.

2. Long-length stubs (such as those longer than 3 meters)

a. Consider their own weight and deflection

Long-length stubs have a large weight and may generate a large tensile force when installed vertically. At the same time, they are prone to deflection when placed horizontally or tilted. For example, in the drilling of inclined wells on offshore drilling platforms, long-length stubs may bend due to their own gravity, affecting the straightness of the drill string. Accurate mechanical calculations are required when using them, and support devices are added when necessary to reduce deflection.

b. Transportation and handling safety

Long-length stubs are more susceptible to damage during transportation and handling. During transportation, use appropriate brackets and fixtures to ensure that the stubs will not be deformed due to vibration or collision. During transportation, use equipment such as cranes for smooth lifting to avoid bending of the stubs or surface scratches due to improper operation.

Diameter Specifications

1. Small diameter pup joints (e.g. less than 100mm)

a. Flow and pressure limitations

In applications involving fluid transmission (e.g. drilling fluid), the internal passages of small diameter pup joints are relatively narrow, which will limit the flow of the fluid and may cause a large pressure drop. When using, the number and position of small diameter pup joints should be reasonably arranged according to the flow and pressure requirements of the system. For example, in drilling operations where the flow of drilling fluid is carefully controlled, it is necessary to determine whether the small diameter pup joints will affect the overall flow through precise calculations, and adjust the pump power or replace the pup joints with appropriate diameters if necessary.

b. Compatibility with other components

When connecting small diameter pup joints with other components (e.g. valves, joints), pay attention to the compatibility of dimensions. Ensure that the connection is well sealed to avoid leakage. Before assembly, the connection components should be strictly checked for size to ensure that the connection tolerance is within the allowable range. The general connection tolerance is controlled within ±0.1 - 0.2mm.

2. Large diameter pup joints (such as those larger than 200mm)

a. Installation space and equipment adaptability

Large diameter pup joints require a larger installation space, and their size should be considered in advance when laying out the equipment. For example, in a narrow space underground, large diameter pup joints may not be installed smoothly, and the borehole size needs to be evaluated and adjusted. At the same time, it is necessary to ensure the adaptability with surrounding equipment (such as drill collars and stabilizers) to avoid mutual interference.

b. Weight and operational difficulty

Large diameter pup joints are usually heavier, which increases the difficulty of installation, removal and operation. During the installation process, large lifting equipment and sufficient manpower are required to ensure safe operation. In addition, due to its heavy weight, the strength requirements of the supporting structure are also higher, and it is necessary to check whether the bearing capacity of the supporting structure meets the requirements.

Wall thickness specifications

1. Thin wall pup joints (such as wall thickness less than 10mm)

a. External pressure and wear resistance

Thin wall pup joints have relatively weak external pressure resistance and are prone to deformation or rupture under high pressure environments. For example, in deep drilling, if you encounter high-pressure formations, thin-walled pup joints may not be able to withstand external pressure. At the same time, their wear resistance is also limited. In high-wear drilling environments, such as hard rock formations, thin walls are easily worn through. When using, carefully select the application scenarios of thin-walled pup joints according to the actual pressure and wear conditions, or take additional protective measures, such as adding an outer protective sleeve.

b. Internal pressure limit

Thin-walled pup joints also have certain limitations when they withstand internal pressure (such as conveying high-pressure fluids). To ensure that the internal pressure does not exceed the limit pressure that the pup joint material can withstand, pressure testing is generally used to verify its safety. Under the design pressure, the safety factor of thin-walled pup joints should not be less than 1.5 to ensure that no safety accidents will occur under normal use and certain pressure fluctuations.

2. Thick-walled pup joints (such as wall thickness greater than 20mm)

a. Weight and cost considerations

Thick-walled pup joints are heavy, which will increase the weight and cost of the entire equipment. When choosing thick-walled pup joints, it is necessary to weigh their strength advantages against the weight and cost increases they bring. For example, in drilling scenarios that do not require excessive strength, excessive use of thick-walled pup joints will increase unnecessary transportation costs and equipment burdens.

b. Heat transfer and thermal stress

When the temperature changes, thick-walled pup joints may generate greater thermal stress due to their thick wall thickness. When used in high or low temperature environments, the effects of heat transfer and thermal stress should be considered. For example, in thermal oil wells, thick-walled pup joints may generate thermal stress due to the large temperature difference between the inside and outside, resulting in damage to the pup joint. Thermal stress analysis is required, and appropriate insulation or heat dissipation measures should be taken.

Summary

In short, when pup joints of different specifications are used in various fields, only by fully understanding these precautions can they play their respective strengths and ensure the smooth progress of the project.