Oil Country Tubular Goods (OCTG)

Oil country tubular goods (OCTG) is a family of seamless rolled products consisting of drill pipe, casing and tubing subjected to loading conditions according to their specific application.

Corrosion resistance under sour service conditions is a very important OCTG characteristic, especially for casing and tubing.

Supply Range

Standard and Grades: API 5CT J55 / K55, N80-1, N80Q, C90, T95, P110, Q125 and 13CrSunnySteel supplies API 5CT casing pipes with the following sizes and specifications:

Casing Pipe Size range: 5 1/2 “to 20” Length usually in R3.

Tubing Pipe dimensions range: 1.0 “, 1.315”, 1.66 “, 1.9”, 2.063 “, 2 3/8”, 3 1/2 “and 4 1 /2”, Length in R2.

Type of connections for Casing: BTC (thread coupling buttress), LTC (long round thread coupling), premium connection.

Types of connections for Tubing: BTC, NUE, EUE, Premium

Each wellbore proceeds in multiple phases, during which

• drill pipe,
• casing (lines the wellbore), and
• tubing (delivery or production tubes that transport the oil and gas to the surface) are used alternately.

The American Petroleum Institute (API) stipulates precisely standardized specifications that define the properties of Oil Country Tubular Goods and classify them into ten grades. These properties are achieved through the chemical composition of the steel and subsequent heat treatment.

Oil Country Tubular Goods are used both onshore and offshore. In the industry, they are also referred to by the acronym OCTG (for “Oil Country Tubular Goods”).

• Drill pipe is heavy seamless tube that rotates the drill bit and circulates drilling fluid. Pipe segments 30 ft (9m) long are coupled with tool joints. Drill pipe is simultaneously subjected to high torque by drilling, axial tension by its dead weight, and internal pressure by purging of drilling fluid.
• Additionally, alternating bending loads due to non-vertical or deflected drilling may be superimposed on these basic loading patterns.
• Casing pipe lines the borehole. It is subject to axial tension by its dead weight, internal pressure by fluid purging, and external pressure by surrounding rock formations. Casing is particularly exposed to axial tension and internal pressure by the pumped oil or gas emulsion.
• Tubing is pipe through which the oil or gas is transported from the wellbore. Tubing segments are generally around 30 ft [9 m] long with a threaded connection on each end.

Typical OCTG manufacturing processes include (all dimensional ranges are approximate)

• Continuous mandrel-rolling process and the push bench process for sizes between 21 and 178 mm OD.
• Plug mill rolling for sizes between 140 and 406 mm OD.
• Cross-roll piercing and pilger rolling for sizes between 250 and 660 mm OD.

These processes typically do not allow the thermomechanical processing customary for the strip and plate products used for welded pipe. Therefore, high-strength seamless pipe must be produced by increasing the alloying content in combination with a suitable heat treatment such as quench & tempering.

Schematic deep well completion

Meeting the fundamental requirement of a fully martensitic microstructure even at large pipe wall thickness requires good hardenability. Cr and Mn are the main alloying elements used to produce good hardenability in conventional heat-treatable steel. However, the requirement for good sulphide stress cracking (SSC) resistance limits their use. Mn tends to segregate during continuous casting and can form large MnS inclusions that reduce hydrogen induced cracking (HIC) resistance.

OCTG includes threaded casing and tubing that are used in equipping and operating oil and gas wells.

Higher levels of Cr can lead to formation of Cr7C3 precipitates with coarse plate-shaped morphology, which act as hydrogen collectors and crack initiators. Alloying with Molybdenum can overcome the limitations of Mn and Cr alloying. Mo is a much stronger hardener than Mn and Cr, so it can easily recover the effect of a reduced amount of these elements.

OCTG Tubing Pipe

OCTG Tubing pipe goes inside the casing pipe because it is the pipe through which oil makes its way out. Tubing is the simplest part of OCTG and it is normally found in the segment of 30 ft (9 m), with threaded connection at both ends. The pipe is either used to transport natural gas or crude oil from the producing formation to the facilities where it will be processed after drilling is complete.

Tubing (pumping pipe) goes inside the casing because it is the pipe through which oil makes its way out. Pipe of production is the simple part of OCTG and it is normally found in the segment of 30 ft (9 m), with threaded connection at both ends. The pipe is either used to transport natural gas or crude oil from the producing formation to the facilities where it will be processed after drilling is complete.