The use of high strength steels in piping used in oil and gas transmission lines, often referred to as “line pipe” is known. Different grades of line pipes such as “X80”, “X90”, and “X100” are also known. The grade terminology refers to the minimum yield strength of the material, i.e. X80 having minimum yield strength of 80,000 pounds per square inch (ksi), X90 having minimum yield strength of 90 ksi, and X100 having minimum yield strength of 100 ksi. In addition, such grades of steel are required to have acceptable toughness properties, i.e. charpy energy and shear area, and drop weight tear test (DWTT) shear area and respective low transition temperatures between ductile and brittle fracture mode. The onset of transition temperature range for DWTT required for specifications such as those of the API (American Petroleum Institute) is taken by the temperature at which at 85% ductile shear area is present on surfaces of a sample that exhibits complete fracture during the test.
Heretofore alloy compositions have included relatively high amounts of alloying elements in order to meet the combination of high strength and high toughness requirements. Naturally, such an increase in alloying elements results in an increase in alloy cost. Therefore, an alloy and a process for producing an alloy that has reduced alloying elements and yet exhibits excellent strength and toughness properties that meet X80, X90 and X100 requirements would be desirable.
USPTO Backgrounds
USPTO Backgrounds