Use this as a prompt list, not a checklist to copy: every node has its own design and causes.
| Deviation | Typical causes | Typical consequences | Typical safeguards |
|---|---|---|---|
| High pressure | Upstream pressure control fails open; gas outlet blocked or closed in error; downstream unit trip; external fire | Overpressure, loss of containment, fire or explosion | Pressure alarm; relief valve sized for the case; high-high pressure SIF closing the inlet |
| Low pressure / vacuum | Outlet open with inlet closed; cooling of a vapour-filled vessel; pump-out without gas supply | Collapse of a vessel not rated for vacuum; air ingress | Vacuum rating; gas blanket; vacuum breaker; low pressure alarm |
| High level | Liquid outlet valve fails closed; downstream pump trip; slug | Liquid carry-over into gas line, compressor or flare | Level alarm; high-high level SIF; knock-out drum downstream |
| Low level | Liquid outlet valve fails open | Gas blow-by to a lower pressure system, overpressure there | Low level alarm; low-low level SIF closing the outlet; downstream relief sized for blow-by |
| High interface | Water boot level control fails | Water carry-over with oil, upset downstream | Interface alarm; manual draining procedure |
| Other than: hydrate, wax, foam | Low temperature, composition change | Blockage, loss of level measurement | Heating, inhibitor injection, alternative measurement |
| Corrosion / erosion | Sand, wet CO₂ or H₂S | Loss of wall thickness, leak | Inspection plan, corrosion monitoring |
Notes: gas blow-by into a lower pressure system is one of the largest relief cases in many plants; check whether downstream relief valves were sized for it.
Written for First Out AI as engineering guidance. It supports engineering work and does not replace it; check every value against your standards, certificates and company rules with a competent functional safety engineer.