Steel pipe toughness index

The toughness index of steel pipe is the same as the strength index of steel pipe, and it is the most important mechanical and physical performance index. The toughness index generally requires requirements from three aspects.


1. Fat index
FATT is the abbreviation of fracture morphology transition temperature, which is usually translated as ductile-brittle transition temperature. FATT can be divided into three types: one is based on DWTT test, the shear temperature (shear area) is 80% or 85%, and the temperature is the transition temperature. This method is used most often with a shear area of 80. The second is based on the Charpy test and the third is based on the burst test.


2. Fracture toughness index
Due to fatigue crack growth, corrosion crack growth, etc., the length of defect 2a (or equivalent crack length) in the steel pipe will gradually increase. When 2a increases to the critical crack length 2ac, a transition from stable crack growth to "mass change" occurs. Unstable swelling. The above a is half of the length of the steel pipe defect or equivalent defect, and ac is half of the critical crack length.


About crack propagation instability
We must make every effort to prevent the pipeline from rupturing, but sometimes it is difficult to completely prevent the rupture, so we must also take a step back, that is, once the rupture occurs, from stable expansion to unstable expansion, unstable expansion must rupture.