CWB Level 2 Study Questions with Detailed Answers

What is the description of damage of a brittle fracture? Sudden rapid fracture under stress (residual or applied) where material exhibits little or no evidence of ductility or plastic deformation What type of Steel are of primary concern with brittle fractures? Carbon and low alloy steels. 400 series SS are also susceptible What has a significant influence on toughness and resistance to brittle fractures? Steel cleanliness and grain size In most cases brittle fractures occur only at what temperature? Below the charpy impact transition temperature.(or ductile-to-brittle transition temperature) The point at which the toughness of the material drops off sharply What kind of equipment or units can be affected for brittle fractures? *Can occur during ambient temperature hydro testing due to high stresses and low toughness at the testing temperature *Most processes run at elevated temperature so the main concern is during startup, shutdown, or hydro/tightening testing. What is the appearance of a brittle fracture? Typically appear straight, non branching, and largely devoid of any associated plastic deformation. (Although fine shear lips may be found along free adge of the fracture or localized necking around neck of crack. What is thermal fatigue a result of ? Cyclic Stress caused by variations in temperature. In thermal fatigue damage occurs as cracking, where may this occur? Can occur anywhere in a metallic component where relative movement or differential expansion is constrained. Particularly under repeated thermal cycling. What type of material can thermal fatigue happen on? All material of construction.