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.
