According to the 1st edition (1988) of the American Petroleum Institute (API) standard API SPEC 5CT, casing steel grades are classified into ten types: H-40, J-55, K-55, N-80, C-75, L-80, C-90, C-95, P-110, and Q-125. Casing is supplied with threads and couplings, or in any of the following end configurations: plain end; round threads (with or without couplings); buttress threads (with or without couplings); integral-joint threads; special end finishes; or seal-ring designs.
Origin
(1) Major countries exporting oil casing to China include Germany, Japan, Romania, the Czech Republic, Italy, the UK, Austria, Switzerland, and the USA; imports also come from Argentina and Singapore. Imported products generally comply with API standards 5A, 5AX, and 5AC. Steel grades include H-40, J-55, N-80, P-110, C-75, C-95, etc. Key specifications include 139.7×7.72 R-2, 177.8×9.19 R-2, 244.5×8.94 R-2, 244.5×10.03 R-2, 244.5×11.05 R-2, etc.
(2) API specifies three length ranges: R-1 (4.88–7.62 m), R-2 (7.62–10.36 m), and R-3 (10.36 m and longer).
(3) Some imported goods are marked "LTC," indicating Long Thread Casing.
(4) Casing imported from Japan generally follows API standards, though a small portion complies with specific manufacturer standards (e.g., Nippon Steel, Sumitomo, Kawasaki); steel grades include NC-55E, NC-80E, NC-L80, NC-80HE, etc. (5) Claim cases have involved surface defects-such as black spots, thread damage, pipe body folds, broken threads, out-of-tolerance thread standoff distances, and out-of-tolerance coupling J-values-as well as internal quality issues like casing embrittlement/cracking and low yield strength.
Packaging
In accordance with SY/T6194-96, domestically produced casing must be bundled using steel wire or steel strapping. Protective rings must be screwed onto the exposed threads of both the casing and the couplings to protect the threads.
