Development of API Grade Pipeline Steel With Improved Toughness on a Compact Strip Production (CSP) Line

Abstract

Oil and gas exploration around the world continues at a rapid pace. This rapid pace of oil and gas exploration in North America has been fueled primarily thorough the development of horizontal drilling and the “fracking” process of underground shale formations. The demand for various grades and dimensions of API casing and pipe has and will continue to increase in the foreseeable future as these shale formations are exploited. To support this demand in North America, Gallatin Steel has embarked on a program to develop API casing and pipe coil skelp via their Compact Strip Plant (CSP). A key characteristic of API grade pipeline steels is excellent fracture toughness. This is one area where historically CSP facilities have struggled, especially in gauges greater than 8.8 mm (0.350″) due to overall lack of reduction from the thin slab design of a CSP facility. In addition, utilizing the typical Thermomechanical Control Processing (TMCP) separating recrystallized and non-recrystallized rolling used in API coil skelp production for strength and toughness of a traditional HSM or plate mill is difficult to achieve in the continuous CSP facility. Gallatin Steel has successfully developed, through a controlled combination of slab quality, alloy design, process modifications and process control, excellent toughness in both charpy and DWTT performance from a 65 mm (2.56″) slab in final coil thicknesses up to 12.7 mm (0.500″). This paper will describe the results achieved to date on various thicknesses from 7.6 mm to 12.7 mm API skelp development at Gallatin Steel. Mechanical property performance along with microstructures/grain size will be presented. In addition, future work that Gallatin Steel will undertake to further improve the capability to produce quality API coil skelp will be discussed.