-
Q What's difference of the coating on casing tube and line pipe?
A The coating on casing tube is a thin “mill varnish” or “shop primer”, mainly used for a short-term rust prevention during storage and transport and identify the steel grade. The coatings on line pipe like FBE, 3LPP, 3LPE are mechanical protection, long-term corrosion resistance, a critical engineered component of the pipeline system.
-
Q What's the different of joint, coupling of OCTG?
A Joint and Coupling refer to specific parts of the pipe assembly. A joint is a single, full-length piece of pipe, typically around 30 ft (Range 2 is most common), can be casing or tubing and usually threaded on both ends. Coupling is the short, thick-walled sleeve used to connect two pipe joints together, a separate piece of steel with threads on the inside of both ends.
-
Q What are the three main categories of OCTG?
A Based on the functional role they play in the drilling and completion process, the three main categories of OCTG are, drill pipe is used to drill the well; casing: is used to line the drilled hole; tubing is used to produce the fluids.
-
Q How are OCTG pipes joined together?
A They are joined by threaded connections, there are two main types, API connections is standard threads defined by the American Petroleum Institute (e.g., ST&C (Short Thread), LT&C (Long Thread), and Buttress); Premium connections is proprietary, high-performance threaded connections designed by companies (like VAM, Tenaris) to provide a 100% gas-tight seal and high torque capacity, which is critical for high-pressure or sour gas wells.
-
Q What is the difference between OCTG and Line Pipe?
A OCTG (Oil Country Tubular Goods) is used inside the harsh downhole environment, is the straw itself and the conduit that brings the oil, gas, water, or other fluids from the bottom to the surface. Line Pipe is used outside the well, the network of pipes that carries the oil, gas, water, or other fluids from the wellhead to the refinery/storage tanks, either buried underground or installed above ground.
-
Q What are the common steel grades for OCTG?
A Based on API Specification 5CT, OCTG steel grades are classified by their minimum yield strength and their suitability for different environments, particularly "sour service". The common grades include: H40 (Low strength, used for shallow wells); J55 / K55 (Low strength, used for shallow wells and surface casing); N80 (Medium strength, used for general casing and tubing); L80 / C90 / T95 ("Sour Service" grades with controlled hardness to resist cracking in H₂S environments); P110 (High strength, used for deep wells and high pressure (sweet service only)); Q125 (Very high strength for extreme depths).
