Temporary pressure increase due to incidental (i.e. transient) conditions.
EXAMPLE Incidental pressure occurs in situations where the pressure increases temporarily due to surge, unintended shut in, well kill (bull heading), failure of a pressure protection system, or other incidental conditions. Incidental pressure can exceed design pressure temporarily.
Source: API Standard 2RD, Dynamic Risers for Floating Production Systems, Second Edition, September 2013. Global Standards