When selecting casing pipes for wells that do not have stringent requirements for anti-corrosion or strength, grades J55 and K55 are popular choices. This article will highlight the differences between these two grades.
Chemical Composition and Physical Properties
Both API grade K55 and J55 share the same chemical composition and yield strength. However, K55 has a minimum tensile strength that is approximately 26% higher than that of J55.
- J55
Yield Strength: 379–552 MPa (55–80 ksi)
Minimum Tensile Strength: 517 MPa (75 ksi)
- K55
Yield Strength: 379–552 MPa (55–80 ksi)
Minimum Tensile Strength: 665 MPa (95 ksi)
Heat Treatment Differences (PSL1 vs. PSL2)
API 5CT J55 PSL1 and API 5CT K55 PSL2 both undergo rolling delivery.
For PSL2, both J55 and K55 must be normalized or normalized and tempered. If the pipes are thickened, normalization or normalizing and tempering should also be applied after thickening.
Impact Test Requirements (PSL1 vs. PSL2)
- Tubing:
PSL1: There are no specific impact test requirements for J55 and K55.
PSL2: Requires a minimum impact work of 20J for a full-size specimen, and 27J for the same specimen.
- Coupling:
Impact tests are mandatory for both J55 and K55. The minimum impact energy required is 20J for the specimen and 27J for the full-size specimen.
API Color Code Differences
J55: Identified by a bright green band, with an additional white band.
K55: Marked by two bright green bands without any additional color.
In summary, while J55 and K55 casing pipes share some similarities, K55 offers higher tensile strength and has distinct requirements for heat treatment and impact testing, making it a more robust option for certain applications.
