A definition that starts with the well
The better starting point is the hole in the ground. A drilled well is an unstable, pressurised tunnel through rock formations that contain water, oil, gas and sometimes corrosive fluids at high temperature. OCTG — oil country tubular goods — is the engineered steel system that turns that hole into a well. Casing lines and supports the hole permanently. Tubing provides the controlled conduit for production. Couplings, pup joints and crossovers join, space and adapt the strings.
This guide groups the term under three broad families. The first is casing: large-diameter pipe, in this factory's published range from 4-1/2 in to 20 in, run in sections called strings. The second is tubing: the smaller string, here in sizes from about 1 in to 3-1/2 in. The third family is accessories — the couplings that join every length, the pup joints that adjust string lengths, the crossovers that connect mismatched components, and the premium connections — the gas-tight patterns the catalogue lists as their own family. This factory's catalogue lists 71 entries across all three families, with couplings the largest single group. The described production and inspection equipment behind the casing entries includes CNC lathes and CNC make-up machines, automatic flaw detection, hydrostatic testing, automatic marking and painting lines, and ultrasonic thickness measurement. Casing packing in the published material is by steel strap or steel frame, or as the customer requires.
Casing: the permanent structure
Grade, weight and thread are designed per interval, and the casing pipe range is organised by those fields.
The published grade list names J55, K55, N80, L80 and P110. In full, the list runs J55, K55, N80-1, N80Q, L80-1 and P110, with the chromium designations L80-3Cr, 9Cr, 13Cr, P110-13Cr and 28Cr alongside. Which grade each interval takes is set by the well design, interval by interval — any hardness limit comes from your specification, stated in the enquiry, not from the grade name alone. Where the produced fluid carries wet CO2, the design may name a chromium grade — the 13Cr series is the chromium family in that list.
Tubing: the working string
If casing is the building, tubing is the plumbing that gets serviced. The tubing string is the string the design places inside the production casing. Tubing carries a different specification emphasis: end finishes — EUE with its upset end, or NUE, the two forms in the published thread-type list — and accessories that space equipment to the depths the design names.
Accessories: where systems are actually joined
No string is pure pipe. Accessories are also where specification discipline matters in practice — a galled coupling thread, a pup joint marked with the wrong length, a crossover threaded to an assumed rather than stated form. The published coupling stock list runs from 1.315 in to 4-1/2 in across eight named sizes. The published text also names conversion joints and crossover couplings as customisable to customer requirements.
The standard behind the system: API 5CT
Casing and tubing are specified to API Spec 5CT, the standard that defines their dimensions, grades, thread forms, gauging and marking. When a buyer orders 9-5/8 in N80 BTC casing, the standard is what makes that line mean the same thing in Tianjin, Houston and Dammam. Thread dimensions and tolerances follow API 5B alongside 5CT, and the specification names three product specification levels — PSL1, PSL2 and PSL3. The published thread-type list names the end forms in that vocabulary — NUE, EUE and the special-clearance form — and the published packing material names cartons, wooden cases and pallets, or packing as the customer requires.
How OCTG is bought
OCTG is not bought from a price list on this site, because price without specification is meaningless in this family. A casing joint's cost depends on size, weight, grade, thread, length range and the mother pipe position behind it; a coupling's cost depends on grade, form and PSL level. State the specification, and the documentation scope the order needs, in the enquiry, and ask for price, MOQ for that specification, packing and lead time to be confirmed for the order in the written quotation.
Premium connections and chromium grades in the modern list
Premium connections sit in the modern list as the gas-tight family, named where the design names one. Chromium grades make corrosion a materials specification the design can name. But the centre holds: casing for structure, tubing for production, accessories for joining and spacing.
Does OCTG include drill pipe and line pipe?
They are tubular products in the same industry, counted separately from the OCTG families on this site. In this factory's current catalogue those families carry no live products, so they are not offered on this site; everything here is casing, tubing and their accessories.
What is the difference between OCTG and casing pipe?
Casing pipe is one family inside OCTG. OCTG is the whole system — casing, tubing, couplings, pup joints, crossovers and premium connections.
Request a Quotation
Send your size, grade, thread and quantity. MOQ, packing and lead time are confirmed in the quotation for your exact specification — no generic promise replaces a written quote.