Assumption Failure Map¶

Map assumptions to plausible failure conditions and their practical consequence.

Working map (CBE 253 example)¶

Assumption	Failure condition	Early signal	Impact on decision	Mitigation
Ethylene selectivity = 78%	Catalyst deactivation after 200 h	Rising byproduct fraction in separator overhead	Utility-priority decision may be wrong; yield dominates economics	Add time-on-stream sensitivity and deactivation factor
Steam cost = $11/GJ	Regional fuel shock to $18/GJ	Weekly utility quote trend > 10%	OPEX underpredicted; design may fail margin target	Run high-price scenario and set utility cap trigger
Pressure drop = 0.25 bar/train	Fouling doubles pressure drop	Compressor load drift and higher suction temperature	Power requirement underestimated	Add fouling contingency case and maintenance interval assumption
No hard purity tightening	Customer spec change to polymer grade	Offtake discussion flags tighter impurity limits	Separation duty and reflux increase	Include high-purity case with explicit CAPEX/OPEX penalty
Feed composition stable within +/-2%	Upstream variability exceeds +/-5%	Analyzer trend shows drift outside control band	Reactor/separation balance shifts; leverage ranking may change	Add feed-variability scenario and refresh baseline each campaign

Risk priority = likelihood (1-5) x consequence (1-5)

Highest current priority: 1. Catalyst deactivation 2. Steam price volatility

Before final recommendation, run sensitivity on the top two assumptions and report whether ranking of design options changes.

These top two risks (selectivity and steam price) feed directly into the next scan: Sensitivity Leverage Scan.