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API-5CT K55 oilfield casing pipe is very similar to J55, there is no significant difference in the chemical composition and yield strength, however the ultimate tensile strength of K55 is higher than J55 steel, K55/J55 are 655MPa and 517MPa respectively.
K55 has better mechanical and thermal fatigue resistance and crack resistance than K55. For a thermal production well, the heavy wall K55 casing is appropriate instead of J55 casing. The former has a better thermal fatigue resistance property than the latter.
In present sales, the selling price of theses two types is generally kept the same, their application is very similar. In the oil drilling, K55 API 5CT casing or tubing is a relatively common type.
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 certication
●Physical and chemicail analysis
●Hardness and pressure test.