Due to their lower price compared to other steel grades, casing pipes of grades J55, K55 are a popular choice for wells without stringent anti-corrosion or strength requirements.In this article we will introduce the difference between K55 and J55.

●Chemical composition and physical properties

API grade K55 has the same Chemical composition as grade J55 ,they both 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