The toughness index of steel pipe
is the same as the index of strength of steel pipe, and it is the most important mechanical and physical performance index. The toughness index generally demands from three aspects.
1, FATT indicators
FATT is the abbreviation of Fracture Appearance Transition Temperature, which is usually translated as "ductile-brittle transition temperature". FATT can be divided into three types: one is based on the DWTT test, and the shear temperature (ShearArea) is 80% or 85%, and the temperature is the transition temperature. This method is the most applied, and the shear area is 80. %, the other is based on the Charpy test and the third is based on the blast test.
2, Cracking toughness index
The length of the defect 2a (or the equivalent crack length) in the steel pipe will gradually increase due to fatigue crack growth, corrosion crack growth and other reasons. When 2a increases to the critical crack length 2ac, the "mass change" occurs, which is changed from stable crack growth. Instability expansion. The above a represents half of the length of the defect or equivalent defect in the steel pipe, and ac is half the length of the critical crack.
3, On the instability of the expansion of the crack
We must make every effort to prevent the pipeline from cracking, but sometimes the cracking is difficult to avoid completely, so we must also take a step back, that is, once the cracking occurs, from stable expansion to instability expansion, the instability expansion must be get cracked.