What does leak before break mean?

Leak-before-break (LBB) is a term that has been used for decades in reference to a methodology that means that a leak will be discovered prior to a fracture occurring in service. LBB has been applied to missile casings, gas and oil pipelines, pressure vessels, nuclear piping, etc.

What is yield before break?

Small pressure vessels are usually designed to allow general yield at a pressure still too low to cause any crack the vessel may contain to propagate (“yield before break”); the distortion caused by yielding is easy to detect and the pressure can be released safely.

Which is highest fracture toughness?

Metals
Fracture toughness varies by approximately 4 orders of magnitude across materials. Metals hold the highest values of fracture toughness. Cracks cannot easily propagate in tough materials, making metals highly resistant to cracking under stress and gives their stress–strain curve a large zone of plastic flow.

How is the leak before Break concept used?

SUMMARY AND CONCLUSIONS Summary The leak before break (LBB) concept is widely used in the nuclear industry to describe the idea that in the piping carrying the coolant of a power reactor a leak will develop before a catastrophic break will occurred.

How does leak before break ( LBB ) work?

The leak area of circumferential through-thickness crack in pipe under bending depends on the position of the crack with respect to the bending plane. In leak-before-break (LBB) analysis, the assumption that the crack is symmetrically placed with respect to the bending plane is not necessarily conservative.

What was the first case of LBB leak?

One of the first few cases associated with LBB was presented by Irwin [1] in the 1960s. According to his work, leakage was predicted to occur due to an axial flaw if the defect length was less than twice the thickness of the pressure vessel.

What are the limitations of leak before break?

Another significant limitation is the requirement on minimum pipe radius. In order to have sufficient margin between the leakage crack size and the critical crack size, pipe dimensions have to be appropriate.