Schneider, Warren P., SPE, Lone Star Steel Co. Summary By use of a simple theoretical analysis, the transverse stresses in couplings and pipe ends of API eight-round and buttress threaded connections caused by makeup and pressures have been calculated and tabulated. Stresses for 680 specified combinations of casing and tubing size, grade, and thread type are examined. Introduction More now than at any other time in the search for petroleum energy reserves, operators are using drilling and production equipment nearer the limits of performance capabilities and, at the same time, facing more costly consequences of failure. The rapid advances in abilities to reach greater depths are challenging designers of equipment that must safely contain the high pressures attendant with today's greater drilling depths. The recent surge in drilling activity has resulted in more frequent encounters with high pressure. Casing and tubing play an important role in both drilling for and extracting oil and gas. Their contribution to the success or failure of the effort and their cost warrant thoughtful design and selection. When unexpectedly high pressures are encountered downhole, these tubulars can be the last defense against loss of equipment, the well, and even lives. It has been established that the use of steel pipe is the most practical means to make a pressure vessel suitable for the drilling and production environment. Many practical considerations require that the pipe be used in separate lengths, each length being joined in sequence as it is lowered into the wellbore. The connection between lengths must sustain high tensile loads and at the same time provide pressure containment from both net internal and external pressures. This connection is made through the joining of threaded pipe ends, most commonly with the aid of a threaded coupling. With the exception of a growing number of proprietary connections, the configuration and specifications of these connections have been standardized through the efforts of the API. To understand the performance of these important connections more thoroughly, the stresses in API round and buttress threaded connections were examined. The results of the application of a previously introduced analysis method to couplings and pipe ends of the full range of sizes, weights, and grades of API casing and tubing are presented. Connection Description API casing thread types include short round thread, long round thread, buttress, and extreme-line. Except for extreme-line, the connections all include use of a coupling. Tubing thread types include nonupset (NUE), external-upset (EUE), and integral joint. NUE and EUE connections use a coupling. This discussion is restricted to short, long, and buttress threaded casing connections and NUE and EUE tubing connections because of predominant use of those connection types. predominant use of those connection types. For each of these types, the union is made by screwing a threaded pipe end into a similarly threaded coupling (Fig. 1). Both pipe and coupling threads are cut on a taper such that at a certain point of engagement the threads of the coupling and pipe come into full intimate contact. This is called the hand-tight position. The thread taper for both pipe end and coupling is specified at 3/4 in./ft on the diameter, except for taper on buttress threads on pipe 16-in. OD and larger, which is 1 in./ft. Two thread profiles are used with these connections: rounded "V", more commonly known as round thread, and buttress (Fig. 2). Thread pitch on casing and tubing round threads is 8 threads per inch, or 10 threads per inch in the smaller tubing sizes. Buttress pitch is 5 threads per inch. As the pipe end advances farther into the coupling through rotation, or makeup, past the hand-tight position, an increasing amount of interference between the pipe and the coupling occurs because of the taper. Expansion of the coupling and compression of the pipe end caused by the wedging action is a major source of tangential, or hoop, stress in both members. The amount of makeup to be applied to a given connection is prescribed. prescribed. JPT p. 1851

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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 pressure wells were drilled, the need for higher performance grades escalated. For wells deeper than performance grades escalated. For wells deeper than about 17,500 feet, economics justified higher performing quality tubulars, yet C-100 or higher performing quality tubulars, yet C-100 or higher performing tubulars remained unavailable. 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 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 properties is derived and its relationship to manufacturing process design and product dimensional compliance is presented for plain-end OCTG casing. Introduction Although the brittle failure of steel under hydrogen sulfide conditions had long been a problem to the materials engineer, failures of API tubing, stainless steel wire lines and alloy steel fishing tools became a severe production problem in the early 1950's. The 1952 NACE symposium on sulfide stress corrosion outlined the basic engineering parameters which guided future metallurgical parameters which guided future metallurgical practice. In March, 1963, the NACE Calgary Area practice. In March, 1963, the NACE Calgary Area T1B Committee issued tentative guidelines for valves and tubular goods for sour service that evolved into the present API C-75 tubular and NACE MR-01-75 materials requirements specifications. The improved sulfide stress cracking resistance of quench and tempered tubular goods led to proprietary "Modified N-80" and "C-90" tubulars which then led to the adoption of API L-80 and work toward C-90 specification. Further processing refinements i.e., full martensitic transformation, high tempering practice, very clean, fine grained steels and low residual stresses have extended the useful minimum strength range of tubulars to 95,000 psi for ambient temperature exposure to wet, sour gas. No manufacturer or user has yet successfully proposed the use of a 100,000 psi or higher minimum yield strength tubular for severe sour gas service. This performance limitation remains a severe obstacle in the completion of deep, highly pressured, sour gas hydrocarbon reservoirs. Following similar materials advances in other industries where improved toughness and imperfection size control were needed to increase performance, Lone Star Steel Company has taken advantage of both metallurgical and dimensional improvement avenues in developing a C-100 performance equivalent, sour gas tubular option. Imperfection size, wall thickness, diameter, ovality and inspectability have been improved beyond API Spec 5AX dimensional requirements so that the necessary improvement in burst and collapse properties may be realized. Steel cleanliness, heat treatment and SSC improvement are features of its new LSS-95 SSGS sour gas product. Combining these dimensional improvements with LSS-95 SSGS metallurgical quality offers a prudent option for achieving a C-100 performance equivalent grade in burst and collapse performance equivalent grade in burst and collapse resistance. DIMENSIONAL QUALITY The simplicity of the tubular shape allows its quality to be easily analyzed by statistical methods amenable to hand held calulators using relatively few measurements of its diameter and wall thickness. Detection and measurement of wall imperfections by nondestructive testing methods improves significantly with the surface quality of the pipe. The frequency and severity of wall imperfections are reduced when surface discountinvities introduced during primary manufacturing steps are removed prior to subsequent hot and cold metal forming operations. P. 33

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This paper combines a report on standardization in the field of reactor dosimetry in the Federal Republic of Germany with an outline of considerations regarding its relationship to the major application, the surveillance of light-water reactor pressure vessels. The paper discusses the interaction between research in the field of reactor dosimetry and the standardization of methods together with the impact of this standardization on practical applications. Part of the work in this field can be considered as being at such a stage that the developed methods can now be applied on a routine basis, relying then on the consequent standardization of successful procedures.