First, what are the common steel grades for oil casing?
According to the American Petroleum Institute standard API SPEC 5CT 1988, first edition, casing steel grades are divided into 10 types: H-40, J-55, K-55, N-80, C-75, L-80, C-90, C-95, P-110, and Q-125. Casing should be supplied with threads and couplings, or supplied with any of the following end types: flat end, round thread with or without couplings, trapezoidal thread with or without couplings, straight thread, special end processing, and sealing ring structure.

Second, what are the common origins of oil casing?
(1) Major importing countries for oil casing include: Germany, Japan, Romania, the Czech Republic, Italy, the United Kingdom, Austria, Switzerland, and the United States. Argentina and Singapore also import from these countries. Import standards mostly refer to American Petroleum Institute standards API 5A, 5AX, and 5AC. The steel grades are H-40, J-55, N-80, P-110, C-75, C-95, etc. The main specifications are 139.77.72R-2, 177.89.19R-2, 244.58.94R-2, 244.510.03R-2, 244.511.05R-2, etc.
(2) API specifies three lengths: R-1 is 4.88~7.62m, R-2 is 7.62~10.36m, and R-3 is 10.36m and longer.
(3) Some imported goods are marked with “LTC,” indicating long threaded sleeves.
(4) In addition to API standards, a small portion of sleeves imported from Japan also follows Japanese manufacturer standards, with steel grades such as NC-55E, NC-80E, NC-L80, NC-80HE, etc.
(5) In claim cases, defects such as blackened threads, damaged threads, pipe folding, broken threads, excessive thread tightness, and excessive J-value of couplings have been found, along with internal quality problems such as brittle casing and low yield strength.

Third, what are the packaging requirements for oil casing?
According to SY/T6194-96, domestically produced casing should be bundled with steel wire or steel strip. Protective rings should be screwed onto the exposed threads of each casing and coupling to protect the threads.