API K55 Casing vs API J55 Casing
These two grades are listed as equivalents of each other: their chemistry windows overlap and they serve the same applications. They are not always identical — check the differences below before substituting, especially in certified designs.
API K55 Casing
Pipe & Tube Steel
K55 sits one step above J55 in the API 5CT casing ladder: the same yield window but a higher minimum tensile strength (655 vs 517 MPa), bought with a slightly richer mill chemistry that API still leaves to the producer. It is the default step-up for deeper or higher-load strings.
Standards: AISI API 5CT K55 · GB K55 (GB/T 19830)
API J55 Casing
Pipe & Tube Steel
J55 is the general-purpose API 5CT casing grade for shallow to medium-depth wells with mild service conditions. API 5CT controls its strength band rather than its chemistry, so J55 pipe is a carbon-manganese steel of mill-selected analysis.
Standards: AISI API 5CT J55 · GB J55 (GB/T 19830)
Chemical composition compared (%)
| Element | API K55 Casing | API J55 Casing |
|---|---|---|
| P | ≤0.030 | ≤0.030 |
| S | ≤0.030 | ≤0.030 |
| Note | API 5CT sets no C/Mn limits for K55 — chemistry is mill practice | API 5CT sets no C/Mn limits for J55 — chemistry is mill practice |
Properties compared
| Property | API K55 Casing | API J55 Casing |
|---|---|---|
| Yield strength | 379–552 MPa (55–80 ksi) | 379–552 MPa (55–80 ksi) |
| Tensile strength | ≥655 MPa (95 ksi) | ≥517 MPa (75 ksi) |
| Density | 7.85 g/cm³ | 7.85 g/cm³ |
Sourcing either grade?
Nasteel stocks both families from Shenzhen with EN 10204 3.1 mill certificates by heat number.
Ask for a quotationSee full data sheets: API K55 Casing · API J55 Casing. Substitution decisions for certified parts stay with the design authority.