The failure assessment diagram (FAD) is a graphical representation of two parameter failure criteria: unstable fracture and plastic collapse. Its application is primarily for crack-like flaws. It is used for HIC and SOHIC mechanisms. We will see FADs in crack assessments.

FFS assessments in API 579 are deterministic; the following types are given:

• Sensitivity assessments multiple assessments are performed to find if small changes in input parameters significantly change the assessment results (e.g., evaluating the effect of toughness on a crack). Spreadsheet software is ideal for this.

• Probabilistic analysis The probability of a failure is determined.

• Partial safety factors They are used to account for uncertain parameters (e.g., crack-like flaws).