API-5CT N80 oilfield casing pipe contains N80-1 and N80-Q types. Those two materials are absolutely consistent regarding the chemical composition and mechanical attributes, they are just various in the heat treatment.
During heat treatment, N80-1 steel is treated by normalizing and tempering, while N80-Q steel is treated by quenching and tempering. Therefore, the collapsing strength and internal pressure strength of N80-Q are higher than that of N80-1. N80-1 or N80-Q should be clearly shown by the designer when N80 casing is selected.
As its mechanical properties are higher than J55 and K55 types, it may very well be utilized to certain a little more challenging formations. With deeper downhole depth than J55 and K55 types, it can be applied for the exploitation of middle-level oil and gas.
Due to the high capability of N80 material, those API 5CT casing pipes are broadly applied in natural gas as well as coal bed methane extraction, and geothermal wells.
Physical properties are checked and each length hydrostatically tested, normally to only 3,000 psi in the plain end (unthreaded) condition. The following are also checked:
Part of this inspection is to drift all lengths.
Despite all the American Petroleum Institute (API) specifications and testing, some tubing defects are still found after delivery; thus, some operators do further inspection.
Size and surface inspection
NDT and pressure test and third party certification
Physical and chemical analysis
Hardness and pressure test.
The difference between N80-1 and N80-Q
In API 5CT specification, for grade N80 there are two different level N80-1 and N80Q. The same part is both N80-1 and N80Q casing pipe have same tensile strength. The different part is impact properties and delivery condition. N80-1 delivery condition is normalizing. The final hot rolled temperature is higher than critical temperature Ar3, and after stretch reducing and air cooling, so could use hot rolled process replace the normalizing. Impact test properties and Non-destructive test is not required.
Heat Treatment is different for N80-1 and N80Q casing and tubing.
For API 5CT N80-Q casing pipe and N80 tubing, the heating treatment should include the quenching and tempering, impact test should comply with API 5CT spec, and Non-destructive test need to be done.