Types and Properties of OCTG Pipe

OCTG stands for Oil Country Tubular Goods and covers several types of pipes and tubes that meet the standards of the American Petroleum Institute (API). OCTG covers three types of seamless tubes that have been quenched and tempered. OCTG drill pipe is heavy, seamless tubing that is used in drill strings for rotating the drill bit and circulating the drilling fluid. Normally 30 feet long, OCTG drill pipe is coupled with tool joints. OCTG casing pipe is pipe used to line the drill hole, and OCTG tubing transports the oil or gas that's produced in the wellbore. OCTG tubing is also around 30 feet long and comes with thread connections on either end.

OCTG Low Alloy Grade Specifications

Low allow steel grades used in OCTG pipe are traditionally carbon-manganese steels, or alloys with up to 0.4% molybdenum. However, in recent years, contaminants in drilling reservoirs and deep drilling applications have increased the demand for OCTG products that are more resistant to sulfide stress cracking and hydrogen embrittlement. For these applications, highly-tempered martensite has been found to be most resistant to sulfide stress cracking. Highly-tempered martensite with molybdenum concentrations of 0.75% offer the best combination of sulfide stress cracking resistance and high yield strength. When even higher yield strengths are needed, the addition of niobium offers yield strengths of up to 140 kilo-pounds per square inch.

OCTG Stainless Steel Specifications

Stainless steel API grades are standardized with 9% chromium plus 1% molybdenum or 13% chromium with no molybdenum. High temperature environments with carbon dioxide and hydrogen sulfide demand improved resistance to corrosion and sulfide stress cracking. Niobium and molybdenum improve corrosion resistance, with molybdenum improving pitting corrosion resistance, thus eliminating areas where sulfide stress cracking can get a foothold.


Mechanical Properties of OCTG Products

OCTG products meeting API 5CT or 5D specifications fall into 16 grades based on minimum yield strength, maximum yield strength, maximum tensile strength, and estimated Rockwell C hardness. For example, grade H-40 has minimum tensile strength of 60,000 psi, minimum yield strength of 40,000 psi, maximum yield strength of 80,000 psi, and estimated hardness of 70 to 87 on the "B" hardness scale, or HRB. At the other end of the scale, Grade S has minimum tensile strength of 145,000 psi, minimum yield strength of 135,000 psi, maximum yield strength of 165,000 psi, and estimated hardness of 32 to 39 (HRB).

Inspection Classifications of OCTG Products

Inspection classifications for new tubing and plain end drill pipe are designated by different colors of banding. White Band products are suitable for all inspections performed, while Yellow Band products are considered repairable rejects. With Yellow Band products, the bands are located on either side of the defect. Blue Band products have imperfections whose depth is undetermined. Red Band items must have body wall defects cut out of the tube for it to be usable. Damaged ends are marked with red bands, and drift restrictions are also designated by red bands located on either side of the restriction.

Your OCTG supplier should be conversant in the various grades and classifications of OCTG piping and tubing so you can be confident you get the exact products your project requires.

Tubing and Casing