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Hazop Guide Words: MORE
pressure#reactor#gas evolution to viscosity#pipe#general
HAZOP guide words and deviations — IEC 61882:2016 guide words applied to common process parameters across node types (pipe, vessel, reactor, heat exchanger, pump, compressor, control loop, batch step), with typical causes, consequences, and safeguards
| guide word | deviation key | context | deviation description | likelihood class | node type | process parameter | severity class | standard | typical causes | typical consequences | typical safeguards |
|---|---|---|---|---|---|---|---|---|---|---|---|
| MORE | pressure#reactor#gas evolution | gas evolution | High pressure in reactor from gas evolution or blocked vent | possible | reactor | pressure | catastrophic | IEC 61882:2016 Table 3; CCPS Guidelines for Hazard Evaluation Procedures 3rd Ed.; API RP 521 | Exothermic gas-generating reaction; vent blockage (ice, polymer, bird nest); decomposition reaction; steam generation | Vessel overpressure; rupture disc failure; catastrophic vessel failure; fire and explosion; toxic release | PRV sized for worst-case scenario per DIERS; rupture disc as backup; vent condenser; high-pressure trip (PAHH); emergency vent |
| MORE | pressure#vessel#general | general | Pressure higher than design or operating limit | possible | vessel | pressure | catastrophic | IEC 61882:2016 Table 3; CCPS Guidelines for Hazard Evaluation Procedures 3rd Ed.; API RP 521 | Blocked outlet; blocked relief valve; upstream pressure surge (water hammer); fire case; exothermic reaction runaway; cooling loss; operator error closing outlet valve | Vessel/line overpressure; rupture; loss of containment; fire; explosion; toxic release; structural failure | Pressure relief valve (PRV); rupture disc; high-pressure alarm (PAH); high-pressure trip (PAHH); depressuring system |
| MORE | reaction#reactor#general | general | Reaction rate or extent higher than intended (exothermic runaway) | unlikely | reactor | reaction | catastrophic | IEC 61882:2016 Table 3; CCPS Guidelines for Hazard Evaluation Procedures 3rd Ed.; DIERS | Loss of cooling; increased catalyst activity; high feed concentration; high feed temperature; inhibitor failure; agitator failure | Temperature and pressure runaway; explosion; fire; toxic release; vessel structural failure | Emergency cooling system (ECS); dump/quench system; high-temperature trip; high-pressure relief; DIERS analysis for two-phase venting |
| MORE | temperature#compressor#general | general | High temperature at compressor discharge (overheating) | possible | compressor | temperature | serious | IEC 61882:2016 Table 3; Crawley et al. HAZOP: Guide to Best Practice 3rd Ed.; API 670 | Compression ratio too high; intercooler failure; cooling water failure; incorrect molecular weight of gas; high suction temperature | Lube oil degradation; bearing damage; seal failure; discharge valve damage; compressor shutdown | Discharge temperature alarm (TAH) and trip (TAHH); intercooler effectiveness monitoring; lube oil temperature indicator |
| MORE | temperature#heat exchanger#general | general | High temperature in heat exchanger shell or tube side | possible | heat exchanger | temperature | serious | IEC 61882:2016 Table 3; Crawley et al. HAZOP: Guide to Best Practice 3rd Ed. | High process inlet temperature; fouling reducing heat transfer; utility temperature higher than design; increased flow rate of hot stream | Tube damage or failure; overpressure on cold side; thermal degradation of process fluid; product quality upset | High-temperature alarm on outlet streams; shell-side and tube-side pressure relief; differential temperature indicator |
| MORE | temperature#vessel#general | general | Temperature higher than intended in vessel | possible | vessel | temperature | serious | IEC 61882:2016 Table 3; CCPS Guidelines for Hazard Evaluation Procedures 3rd Ed. | Loss of cooling water; cooling control failure; exothermic reaction; heat exchanger fouling; fire; solar radiation; steam tracing failure | Overheating of materials; degradation of product; overpressure from thermal expansion; runaway reaction; structural weakening; fire | High-temperature alarm (TAH); temperature controller; cooling water flow switch; emergency cooling; high-temperature trip (TAHH) |
| MORE | viscosity#pipe#general | general | Viscosity higher than design intent | possible | pipe | viscosity | minor | IEC 61882:2016 Table 3; Crawley et al. HAZOP: Guide to Best Practice 3rd Ed. | Low temperature; change in product composition; polymerization; fouling; gelling of slurry | Increased pressure drop; pump overload and damage; poor mixing; plugging of lines and instruments; heat transfer degradation | High viscosity alarm (derived from DP); temperature control; inline viscometer; minimum temperature interlock |
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