Besides API 5L lipe pipes for oil and gas transportation, API 5CT is widely used in oil drilling platforms, it has been classified into common grade types and special types for fierce environment,for example,corrosive and abrasion. In common applications, most casing tube grades are largely of the same chemical composition. What gives each grade its distinct properties is the kind of heat treatment applied. Casing grades mainly differ in their yield strength, tensile strength, and hardness.
Additional tests required by API 5CT for certain groups of casing make sure that each casing grade is suitable for its intended application.
Common Application Casing (H40, J55, K55, M65, N80, R95)
Due to their lower price compared to other steel grades, casing pipes of grades J55, K55, and N80 are a popular choice for wells without stringent anti-corrosion or strength requirements.
M65, and R95 are newer grades, each with their own field of application. These casing grades mainly differ in their yield strength and tensile strength.
| Casing Pipe Types | Yield Strength | Minimum Tensile Strength | API Color Code |
|---|---|---|---|
| H40 | 276-552 MPa (40-80 ksi) | 414 MPa (60 ksi) | Either none or 1 black band |
| J55 | 379-552 MPa (55-80 ksi) | 517 MPa (75 ksi) | 1 bright green band |
| K55 | 379-552 MPa (55-80 ksi) | 665 MPa (95 ksi) | 2 bright green bands |
| M65 | 448-586 MPa (65-85 ksi) | 586 MPa (85 ksi) | 1 bright green band + 1 blue band |
| N80-1/Q | 552-758 MPa (55-80 ksi) | 689 MPa (100 ksi) | 1 red (N80-1), 1 red band + 1 bright green band (N80-Q) |
| R95 | 655-758 MPa (95-110 ksi) | 727 MPa (105 ksi) | 1 brown band |
Application Fileds of API 5CT Pipe Grades
- K55: API grade K55 has the same yield as grade J55, but its minimum tensile strength is about 26% higher compared to J55.
- M65: Not used that often, M65 is the only steel grade among the general purpose casing grades with the requirement of a restricted maximum hardness.
- N80(N80-1, N80-Q): Both N80-1 and N80-Q have the same yield strength and tensile strength, but N80-Q, which is quenched and tempered, shows a higher resistance to internal pressure and collapsing. On the other hand, casing N80-1 is cheaper to produce and the first choice were a higher collapse resistance in not needed.
- R95:Same yield strength range and tensile strength as grade T95, but without the requirement for SSC or hardness tests. Steel grade R95 therefore is a better-priced alternative to T95 in wells without the risk of sulfide stress cracking.
