Unsuccessful exposure to hydrogen sulfide containing production fluids occurred in API N-80 and P-110 grades in the early 1950's and prompted the development of metallurgically improved and strength restricted C-75, L-80 and C-90 grade tubulars for sour service. As deeper, higher pressure wells were drilled, the need for higher performance grades escalated. For wells deeper than about 17,500 feet, economics justified higher performing quality tubulars, yet C-100 or higher performing tubulars remained unavailable.
Following similar developments in other industries facing a need for higher performing, fracture resistant materials, Lone Star Steel Company has combined advanced metallurgical and processing techniques with ID and OD imperfection removal and cold forming steps to upgrade both dimensional control and steel quality of tubulars. The result is a more conservative approach which conveys C-100 performance for the LSS-95 SSGS grade. A method for statistical analysis of dimensional properties is derived and its relationship to manufacturing process design and product dimensional compliance is presented for plain-end OCTG casing.