Quality standards for oil casing pipe

The quality standards for oil casing pipe primarily include the following aspects:

1. Chemical Composition

The chemical composition of oil casing pipe should comply with relevant standards. For example, the carbon (C) content is typically between 0.22% and 0.28% to ensure sufficient strength and toughness; the manganese (Mn) content is generally between 0.30% and 1.20%, which helps improve the strength and hardenability of the steel; and the silicon (Si) content is approximately 0.15% to 0.35%, which increases the hardness and elasticity of the steel. Strict control of the chemical composition ensures that the casing performs well in the harsh oil production environment.

2. Mechanical Properties

a. Tensile Strength: Oil casing pipe requires high tensile strength to withstand the tensile stresses experienced during drilling. The tensile strength is generally required to be between 485 and 620 MPa to ensure it does not break during use.
b. Yield Strength: Yield strength reflects the casing's ability to resist plastic deformation and is typically in the range of 345-450 MPa. A high yield strength ensures that the casing remains stable under pressure and resists deformation.
c. Impact Toughness: Due to the complex environment of oil production, casing may be subjected to impact loads. Therefore, casing must exhibit good impact toughness, typically with an impact energy absorption rating of at least 47 J, to prevent rupture under low temperatures or sudden impact.

3. Pipe Quality

1) Pipe Dimensional Accuracy: Dimensions such as the outer diameter and wall thickness of oil casing pipe must meet strict tolerances, with deviations kept to a minimum to ensure proper compatibility with other drilling equipment and avoid gaps or overtightening during installation and operation.

2) Pipe Surface Quality: The pipe surface should be smooth, free of defects such as cracks, folds, and scarring. Rust and pitting that could affect performance should be avoided. Good surface quality improves the casing's corrosion resistance and sealing properties, reducing resistance and risks during drilling.

3) Pipe Ovality: The ovality of the pipe body should be controlled within a certain range, generally not exceeding a certain percentage of the outer diameter tolerance, to ensure smooth passage of the casing through drilling equipment and avoid accidents such as drill sticking due to excessive ovality.

4. Joint Quality

a. Joint Thread Accuracy: The threads of oil casing joints must be machined with high precision. Parameters such as thread pitch and profile angle must meet standard requirements to ensure tightness and reliability. The thread surface should be smooth and free of defects such as burrs and cracks to prevent damage to the threads and leakage during connection and disassembly.

b. Joint Tensile Strength: The tensile strength of the joint should be no less than that of the pipe body to ensure that the strength of the entire casing meets drilling requirements after connection. The tensile strength of the joint is generally required to be similar to that of the pipe body to ensure the integrity and safety of the entire casing.

c. Sealing: The sealing of the joint is crucial and should be ensured through rigorous sealing tests. Under certain pressure and temperature conditions, joints must be leak-free to prevent oil and natural gas leaks and ensure safe drilling operations.

5. Corrosion Resistance

Oil casing operates in humid, corrosive environments underground, so it requires excellent corrosion resistance. Surface treatments such as galvanizing and copper plating, or the use of corrosion-resistant alloy steels, are commonly used to extend the casing's service life and reduce maintenance costs.

6. Non-destructive Testing

To ensure the quality of oil casing, rigorous non-destructive testing (NDT) is required. Common NDT methods include ultrasonic testing, magnetic particle testing, and eddy current testing. These methods can promptly detect internal and surface defects such as cracks, slag inclusions, and pores, preventing defective casing from being put into service and ensuring safe and smooth drilling operations.

Manufacturing Process:

The production process for oil casing pipe primarily involves hot rolling and cold drawing. Hot rolling involves heating the steel billet to a high temperature before rolling. This process allows for the production of larger diameter and thicker wall casing, offering high efficiency and low cost. The production process includes steelmaking, rolling tube billets, heating, piercing, rolling, sizing, and cooling. The cold drawing process involves drawing the tube at room temperature, which improves the precision and surface quality of the casing. Hot-rolled tubes are typically pre-treated with pickling and phosphating before being drawn through dies multiple times. 

Alternatively, there is the welding process, which involves welding steel strips or plates into casing. This is suitable for non-critical locations or cost-sensitive applications. Different production processes are suitable for different casing specifications and performance requirements.

Conclusion:

The quality standards for oil casing pipe are extremely stringent, covering multiple aspects such as chemical composition, mechanical properties, pipe quality, joint quality, corrosion resistance, and NDT. Only oil casing that meets these standards can play a good role in oil production and ensure the safety and efficiency of drilling operations.

Read more: API 5CT Steel Casing and Tubing Chart or OCTG Casing Pipe Steel Grade