I. Introduction to API J55 Oil Well Steel Casing
API J55 oil well steel casing is a low-medium strength carbon steel that complies with the API 5CT standard and is widely used as surface or intermediate casing in oil and gas wells.
It offers excellent mechanical and processability, withstands downhole pressure, and supports the wellbore. Anti-corrosion treatments (such as external rust-proof oil or epoxy coating) enhance corrosion resistance, ensuring safe and reliable downhole operations. It is suitable for shallow wells and conventional well sections.
II. API 5CT oil well steel casing multiple steel grade comparison table
| Steel Grade | PSL Grade | Carbon (C %) | Manganese (Mn %) | Yield Strength (MPa) | Tensile Strength (MPa) | Elongation (%) | Applicable Well Section |
|---|---|---|---|---|---|---|---|
| J55 | PSL-1 / PSL-2 | ≤0.35 | 0.30–1.06 | 379–552 | 517–690 | ≥15 | Shallow wells, conventional wells |
| K55 | PSL-1 / PSL-2 | ≤0.35 | 0.30–1.06 | 379–552 | 517–690 | ≥15 | Shallow wells, conventional wells |
| N80 | PSL-1 / PSL-2 | 0.28–0.45 | 0.30–1.20 | 552–689 | 689–827 | ≥15 | Medium-deep wells, high-pressure wells |
| L80 | PSL-1 / PSL-2 | 0.17–0.25 | 0.30–0.90 | 552–655 | 655–758 | ≥12 | Medium-deep, high-pressure wells; for corrosive wells use L80-1 / L80-9 |
| P110 | PSL-1 / PSL-2 | 0.25–0.35 | 0.30–1.20 | 758–965 | 827–965 | ≥12 | Deep wells, high-pressure wells, high-temperature or corrosive wells |
Table Description
Steel Grades: Arranged from lowest to highest strength: J55/K55 → N80 → L80 → P110;
PSL Grade: PSL-2 has stricter chemical composition control and testing, suitable for wells requiring a high safety factor;
Chemical Composition: Carbon (C) and manganese (Mn) are key control elements;
Mechanical Properties: Yield strength and tensile strength increase with increasing steel grade;
Elongation: Ensures sufficient ductility of the casing under downhole stress;
Applicable Well Sections: Shallow, medium-deep, deep, and corrosive well sections. Steel grades are selected to suit different operating conditions.
III. PSL Level Selection Instructions
| PSL Grade | Features | Applicable Well Section | Remarks |
|---|---|---|---|
| PSL-1 | Basic level, relatively loose chemical and mechanical property requirements | Shallow wells, conventional well sections | Lower cost, suitable for general oil and gas wells |
| PSL-2 | Stricter chemical, mechanical, and testing requirements; high-quality control | Medium-deep wells, high-pressure wells, corrosive wells, high-temperature wells | High safety factor, suitable for critical well sections, slightly higher price |
IV. API 5CT Oil Well Steel Casing Dimensions and Lengths
Outer Diameter (OD): Commonly 114.3–355.6 mm; larger diameters can be customized for special well sections.
Wall Thickness (WT): 6–15 mm. Selection is based on downhole pressure, load bearing, and casing weight.
Nominal Lengths: R1: 4.88–7.62 m, R2: 7.62–10.36 m, R3: 10.36–14.63 m.
Purchasing Recommendation: Select length and specifications based on well depth, construction equipment, and transportation conditions to avoid construction difficulties caused by excessive or insufficient length.
V. API 5CT oil well steel casing thread and end processing
| Parameter Category | Description | Purchasing Suggestions |
|---|---|---|
| Thread Type | STC / LTC / BTC | Confirm thread type matches wellhead equipment to avoid incompatible installation |
| Thread Length | ≥50 mm (end thread length) | Ensure connection strength meets downhole operation requirements |
| Thread Precision | Machined according to API 5CT standard | Request suppliers to provide machining quality assurance to guarantee sealing performance |
| End Protection | Casing ends protected with plastic or steel caps | Prevent thread damage during transportation and storage |
| Cutting Tolerance | ±1 mm | Ensure casing length meets design requirements and facilitates field connection |
VI. API 5CT oil well steel casing inspection items and inspection standards
| Inspection Category | Inspection Item | Standard / Method | Description |
|---|---|---|---|
| Chemical Composition | C, Mn, S, P | API 5CT / Spectral Analysis | Ensure steel chemical composition meets grade requirements, affecting mechanical properties and corrosion resistance |
| Mechanical Properties | Yield Strength, Tensile Strength, Elongation | API 5CT / Tensile Test | Guarantee casing pressure capacity and toughness |
| Dimensional Accuracy | Outside Diameter, Wall Thickness, Nominal Length | API 5CT / Dimensional Measurement | Ensure wellhead compatibility and smooth installation |
| Geometric Accuracy | Bend, Straightness, Ovality | API 5CT / Geometric Measurement | Ensure smooth casing running and reduce sticking risk |
| End Threads | Thread Type, Thread Precision, Thread Length | API 5CT / Thread Gauge | Ensure reliable connection and sealing of the casing |
| Surface Quality | Internal & External Roughness, Mill Scale, Rust | API 5CT / Visual Inspection or Roughness Measurement | Affects anti-corrosion treatment and running friction |
| Hydrostatic Test | Static Pressure Capacity | API 5CT / Hydrostatic Test | Verify casing can withstand downhole working pressure |
| Nondestructive Testing (NDT) | Ultrasonic, Eddy Current, Magnetic Particle | API 5CT / NDT | Detect internal defects, cracks, or inclusions to ensure quality |
| Heat Treatment Record | Normalizing, Quenching & Tempering | API 5CT / Manufacturer Record Verification | Ensure uniform mechanical properties and microstructure |
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