Comparing to other steel grades, casing pipes of grades J55, K55 are a popular choice for wells without stringent anti-corrosion or strength requirements. Here, we will introduce  you the difference between K55 and J55.

Chemical composition and physical properties

API grade K55 has the same Chemical composition as grade J55, both of them has the same yield, but its minimum tensile strength is about 26% higher compared to 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 (PSL2 and PSL1 are different)

API 5CT J55 PSL1 and API 5CT K55 PSL2 is the same (Rolling delivery);

PSL2 :J55 and K55 should be normalized or normalized and tempered. If thickened, normalizing or normalizing and tempering should be added after thickening.

Impact test (PSL2 and PSL1 are different)

Tubing: PSL1, J55 and K55 have no requirement; PSL2 J55 and K55 require minimum impact work 20J of full size specimen, and minimum impact work 27J of full size specimen.

Coupling: J55 and K55 impact tests are necessary. The minimum impact energy of the specimen is 20J, and the minimum impact energy of the full size specimen is 27J.

API color code (ribbon difference)

J55:bright green band.The band is bright green with a white band

K55:2 bright green bands with no additional band