For API 5CT oil casing, hardness is a very important indicator. Only oil casings with qualified hardness can ensure the effect during use. On the contrary, if the hardness is unqualified, problems are likely to occur during use. Accidents can cause danger. If you want to know the hardness of API 5CT oil casing, you can actually test the oil casing through experiments.
1. Tensile test
The tensile test is to make a sample of API 5CT petroleum casing, pull the sample to fracture on a tensile testing machine, and then measure one or more mechanical properties. Usually only tensile strength, yield strength, and elongation after fracture and area reduction are measured. Tensile test is the basic mechanical property testing method of API 5CT petroleum casing.
2. Hardness test
The hardness test is to use a hardness tester to slowly press the hard indenter into the surface of the API 5CT oil casing sample under specified conditions, and then test the indentation depth or size to determine the material.
Chemical compositions of casing pipe
| Standard | Grade | Chemical compositions(％) | |||||||||
| API SPEC 5CT | J55 | C | Si | Mn | P | S | Cr | Ni | Cu | Mo | V |
| K55 | 0.34～0.39 | 0.20～0.35 | 1.25～1.50 | ≤0.020 | ≤0.015 | ≤0.15 | ≤0.20 | ≤0.20 | / | / | |
| N80 | 0.34～0.38 | 0.20～0.35 | 1.45～1.70 | ≤0.020 | ≤0.015 | ≤0.15 | / | / | / | 0.11～0.16 | |
| L80 | 0.15～0.22 | ≤1.00 | 0.25～1.00 | ≤0.020 | ≤0.010 | 12.0～14.0 | ≤0.20 | ≤0.20 | / | / | |
| P110 | 0.26～0.395 | 0.17～0.37 | 0.40～0.70 | ≤0.020 | ≤0.010 | 0.80～1.10 | ≤0.20 | ≤0.20 | 0.15～0.25 | ≤0.08 | |
Mechanical properties of casing pipe
| Grade | Type |
Total elongation under load (%) |
Yield strength (min)Mpa |
Yield strength (max)Mpa |
Tensile strength min Mpa |
Hardness Max (HRC) |
Hardness Max (HBW) |
| J55 | - | 0.5 | 379 | 552 | 517 | - | - |
| K55 | - | 0.5 | 379 | 552 | 655 | - | - |
| N80 | 1 | 0.5 | 552 | 758 | 689 | - | - |
| N80 | Q | 0.5 | 552 | 758 | 689 | - | - |
| L80 | 1 | 0.5 | 552 | 655 | 655 | 23 | 241 |
| L80 | 9Cr | 0.5 | 552 | 655 | 655 | 23 | 241 |
| L80 | 13Cr | 0.5 | 552 | 655 | 655 | 23 | 241 |
| C90 | - | 0.5 | 621 | 724 | 689 | 25.4 | 255 |
| C95 | - | 0.5 | 655 | 758 | 724 | - | - |
| T95 | - | 0.5 | 655 | 758 | 724 | 25.4 | 255 |
| P110 | - | 0.6 | 758 | 965 | 862 | - | - |
| Q125 | All | 0.65 | 862 | 1034 | 931 | - | - |
