What are differences between J55 and K55 casing in API 5CT?
1. Heat Treatment
For PSL1, both J55 and K55 casing can be delivered in rolled condition; For PSL2, J55 & K55 casing should be delivered in normalized or normalized & tempered condition, if the casing are thickened, they should be made normalization or normalization & temper after thickening.
There is no different requirement for straightening the J55 and K55 casings.
3. Chemical Component
For J55 and K55, except the chemical component P≤0.03% & S≤0.03%, there is no requirements for other chemical component.
4. Mechanical Test
The yield strength for J55 & K55 are same in 379-552MPa, but the tensile strength is different, the tensile strength of J55 is ≥517MPa and the tensile strength of K55 is ≥655MPa.
Because of different tensile strength, so the elongations are also different. The elongation of J55 is ≥19%, while the elongation of K55 is ≥15%.
5. Impact Test
For casing body, there is no technical requirement, if J55 & K55 are in PSL1 class. If J55 & K55 are in PSL2 class, the impact test for casing body is required. The minimum Impact energy of full-scale sample is 20J in horizontal direction and 27J in longitudinal direction.
For casing couplings in PSL1 and PSL2 class, the impact test must be done. The minimum Impact energy of full-scale sample is 20J in horizontal direction and 27J in longitudinal direction.
6. Hydrostatic test
There is no requirements for both J55 and K55 grade.
7. Thickness Inspection
For class PSL1, the inspection of wall thickness is no requirements for J55 and K55.
For class PSL2, the inspection of wall thickness should be made over entire length of casing for both grade J55 and K55, and the inspection covered surface should be at least 25% by auto detection system.
8. Non-destructive Test
For class PSL1, the inspection of wall thickness is no mandatory requirements for J55 and K55.
For class PSL2, the non-destructive test for inner and outer surface be made by one or several methods in 10.15.5 specification of API 5CT to ensure the longitudinal defects can meet the Level 4 specification.
For grade J55, the casing body should be painted a bright green band; the coupling should be painted a bright green with an additional white band on it.
For grade K55, the casing body should be painted two piece of bright green bands; the coupling should be painted only one bright green band without any additional colored band.