The API 5CT standard covers seamless and welded casing and tubing pipes for oil and gas transportation.Casing pipes are available in the following materials: H-40, J-55, K-55, N-80, L-80, C-90,T-95 ,P-110, Q-125.
Depending on the different condition and the depth of the well,we should use the different steel grades.The corrosion resistance of the casing is also required under the corrosive environment. In the case of complex geological conditions, the casing has to be resistant to collapse.Most casing steel 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.
According to API 5CT,there are four groups of products to API SPEC 5CT is applicable include the following grades of pipe:
Group 1: Grades H, J, K,M, N and R;
Group 2: Grades C, L and T;
Group 3: Grade P;
Group 4: Grade Q.
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.
Corrosion-Resistant Casing (L80，C90，T95, C110)
API 5CT steel grades L80-1, C90, T95, and C110 show a higher resistance to sulfide stress cracking in H2S environments due to lower limits of sulfur and phosphorous as well as the addition of the following mandatory tests:
Casing grades L80-9Cr and L80-13Cr are suitable for application in CO2 environments, mainly because of their higher chromium content.
Deep Well Casing (P110, Q125)
With the highest yield strengths among all API 5CT casing grades, P110 and Q125 are ideally suited for high pressure formations in deep wells.However, as steel becomes more susceptible to sulfide stress cracking the higher the yield strength, both grades should not be used in H2S environments.