New favorite of offshore pipe

In the seamless line pipe standards of the past, such as API 5L (American petroleum institute standards) setting the highest strength of seamless line pipe for X80 (lower limit yield strength of 555 Mpa), almost no strength higher practical example of seamless line pipe.With the improvement of strength, generally speaking, fear that the toughness of the parent metal and circumferential welding will decline.Therefore, in order to make the base at the same time to achieve high strength, high toughness and good weldability of the circle, must develop new steel tube material.In addition, the top tension stand tube plays a role of connecting the wellhead and offshore platform directly, and protecting the production fluid circulation pipe, so it must withstand the anti-fatigue properties of waves and tides impact.To solve the above problems, Nippon steel developed the high strength X90 - X100 seamless steel pipe for line pipe and rising pipe.Developed by Nippon steel of high strength welded X90 - X100 seamless line pipe through the alloy design ensures the strength of parent metal, and ensures the toughness, by reducing the C content at the same time to improve the welding of toughness, thus satisfy the performance requirements including circular weldability. Steel pipe diameter and wall thickness are 323.9 mm and 20.0 mm respectively.To evaluate the characteristics of the circumferential welding department, for the whole of weld metal of the tensile test, vickers hardness test, CVN test and CTOD test.Experiment shows that there are no obvious hardening in the HAZ.Set the changing range of the stress ratio R of X90 steel pipe in 1 ~ 0.7, carrying out high cycle fatigue tests. When the stress ratio R is 0.05, fatigue limit is 650 Mpa, at this time of stress amplitude is 325 Mpa, the average stress is 359 Mpa. X90 steel pipe material in various stress ratio under the condition of fatigue limit and is considered to be the most stringent fatigue limit diagram of equal to or higher than the Gerber chart, so it has good fatigue properties. Besides, the fatigue limit of X90 welded joint is the same as other steel pipe parent material, has good fatigue characteristics, to meet the requirements of customers.