Oil Country Tubular Goods are used both onshore and offshore. OCTG refers to a wide range of rolled metal products, more commonly known as pipes. There are various accessories included in their manufacture and processes. This can include drill casing or tubing pipes, thread protectors, stabbing guides, bumper rings and pipe chocks. The piping products qualify as OCTG due to the specifications of each pipe in regards to their acceptable loading conditions, and/or what they can transfer, how strong they are, and their composition.
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 well-bore. Tubing segments are generally around 30 ft [9 m] long with a threaded connection on each end.
Typically, OCTG manufacturing processes include continuous mandrel-rolling processes and push bench processes for tubular goods sized between 21 and 178 mm OD. For sizes anywhere from 140 to 406 mm OD, plug mill rolling is used.
As you might imagine, oil country tubular goods have a base standard requirement of extremely dependable hardness, usually referred to as having a martensite structure (super hard). To meet these standards, chromium and manganese are used as the main alloys to help confirm high cohesion and durability. The main issue that arises comes from sulfide stress cracking, which originates from the actual drilling into deep earth. Not only is the pressure immense at those levels, but the drilling itself causes creation of particles that quicken corrosion.