Manufacturing Process of Oil Casing Pup Joints

In the oil and gas industry, oil casing pup joints are important components for connecting casing pipes. Their quality and performance directly affect the safety and sealing of the entire downhole pipeline system. In order to ensure its stable and reliable mechanical properties, oil casing pup joints are usually processed with the seamless steel pipe and formed by different process methods. This article will deeply analyze the two main production processes of pup joints: hot rolling process and cold drawing (cold rolling) process.

Process of hot-rolled seamless steel pipes

Hot rolling is one of the most common processes for producing oil casing pup joints, which is suitable for the manufacture of large-diameter and high-strength steel pipes. The basic process is as follows:

Hot rolling process

Round tube billet → heating → perforation → three-roller oblique rolling, continuous rolling or extrusion → tube removal → sizing (or diameter reduction) → cooling → straightening → hydraulic pressure test (or flaw detection) → marking → storage

1. Heating and perforation

The billet is heated to about 1200℃ to improve plasticity and facilitate perforation forming.

2. Oblique rolling/continuous rolling/extrusion

Through three-roller oblique rolling or continuous rolling mechanism, the solid billet is transformed into a hollow rough tube.

3. Sizing/reduction

Further shaping is performed according to the required size to ensure the consistency of the tube body size.

4. Hydraulic pressure test/flaw detection

The strength and sealing of the tube body are fully tested to meet industry standards such as API 5CT.

5. Final processing

Marking and storage to ensure quality traceability.

Hot-rolled pup joints are widely used in OCTG pipe systems due to their high production efficiency and wide range of sizes, especially in operating environments with deep wells and large temperature differences.

Process of cold-drawn (cold-rolled) seamless steel pipe

Compared with the hot-rolled process, the cold-drawn (rolled) process is more suitable for manufacturing short-section products with higher dimensional accuracy and better surface quality.

Cold-drawn process

Round tube billet → heating → perforation → heading → annealing → pickling → oiling (or copper plating) → multiple cold drawing (or cold rolling) → billet tube → heat treatment → straightening → water pressure test (or flaw detection) → marking → storage

1. Perforation and heading

A preliminary hollow tube body is formed to prepare for subsequent drawing.

2. Pickling + oiling/copper plating

Remove oxide scale, improve surface lubricity, and improve drawing quality.

3. Multiple cold drawing/cold rolling

Precisely control the tube diameter and wall thickness to improve the dimensional consistency and surface accuracy of the product.

4. Heat treatment and straightening

Improve the toughness of steel and prevent stress concentration caused by cold processing.

5. Inspection and marking

Ensure no cracks and no leaks through water pressure test and non-destructive testing.

Cold drawn pup joints are usually suitable for application scenarios that require high dimensional accuracy, high finish and low tolerance, such as precision instrument joints, special oil well operations, etc.

Summary

High-quality oil casing pup joints not only improve downhole operation efficiency, but also effectively reduce operation risks. Choosing the right production process is the key to ensuring the safe operation of oil and gas pipeline systems.