Hand-considered hypotheses, 5101–5200
Petroleum refining and petrochemicals, written one at a time. Crude and vacuum distillation, fluid catalytic cracking, hydrotreating, delayed coking, corrosion in process units, and the product properties that follow from them. The claim in each entry is a mechanism, a bound or a diagnostic argument, and the logical form chosen for it is printed above the text so the variety can be checked rather than trusted. None has been tested; no citation is given because none is invoked, and every quantity offered as an estimate is marked as one.
Crude distillation and fractionation
Misattribution to the wrong phase
H5101. Dry point is usually read as the heaviest molecule that distilled, but in an entraining column it is set by the largest droplet that survives the demister. Change the demister mesh at a fixed cut point and the dry point should move while the true boiling curve does not.
Hidden term
H5102. A kerosene side draw’s flash point carries a hidden term from light ends dissolved in the draw, and the stripper reboiler cannot remove them because its vapour returns to the main column. Flash point is therefore a stripper-pressure measurement as much as a composition measurement, separable by a pressure step at constant draw.
Inversion at a hydraulic limit
H5103. Raising reflux is supposed to sharpen a crude tower’s split, but the rule inverts on trays that are already weeping. The extra liquid loads the downcomer, raises the clear liquid height, and pushes vapour through the sieve holes as a coarse jet. The split then worsens with reflux, and the turnover should appear as a step in tray pressure drop.
Geometric bound
H5104. Heavy-cut recovery in a vacuum tower is bounded by the vertical clearance between wash zone and flash zone, not by ejector capacity. That clearance fixes the maximum vapour velocity the wash section tolerates without re-entraining liquid, and an estimate from flash-zone diameter puts the bound within a factor of two of the mechanical limit.
Threshold set by a dimensionless group
H5105. Entrainment from a crude tower flash zone should begin at a Froude number built on vapour density, droplet diameter and flash-zone diameter, not at a fixed vapour rate. If that holds, the threshold follows from tower diameter alone and can be checked by raising feed rate at two pressures.
Two mechanisms conflated
H5106. Loss of tray efficiency is usually charged to poor contacting, but vapour backmixing in the downcomer and liquid crossflow maldistribution produce the same apparent efficiency. A tracer test at two liquid loads separates them, because backmixing scales with downcomer residence time while maldistribution scales with flow path.
Trend artefact
H5107. A pilot column’s cut point can appear to rise over a run because the reboiler is fouling and its wall temperature is climbing, not because the feed changed. Holding boil-up constant and repeating with a clean reboiler exposes the artefact.
Mean hiding a distribution
H5108. Two gasolines with the same ninety-five percent point can drive differently when one boiling curve is bimodal and the other smooth, because the heavy mode controls the last evaporating fraction and the light mode controls the front. The specification number is a mean over a distribution it does not resolve.
False linearity
H5109. Overhead temperature responds linearly to reflux only while the condenser is fully flooded. Once it is partly drained the response acquires a hold-up lag that a linear fit misreads as gain. A step test at two condenser inventories should show the break.
Pressure-swing separation limit
H5110. Pressure-swing distillation cannot separate a pair whose relative volatility stays close at both operating pressures, and the practical limit is the ratio of the two vapour-pressure slopes. Nearly equal slopes mean no pressure window worth building, however pure the specification.
Theoretical-stage ambiguity
H5111. Stage count cannot be inferred from terminal compositions alone, because different combinations of stages and reflux reproduce the same separation. A stage efficiency derived from terminal data is not unique, and an independent tracer residence-time measurement is needed to break the degeneracy.
Relative volatility inversion
H5112. Relative volatility of two close-boiling aromatics in a reformate splitter can invert near the tray temperature where their activity coefficients cross, so a small pressure change reverses which component leaves overhead. The inversion should appear as a sign change in the splitter’s reflux response and is a cleaner diagnostic than product purity.
Residence time distribution
H5113. True separation in a packed vacuum column is set by the liquid’s residence-time distribution in the packing, and a small stagnant fraction can hold heavy material that desorbs later and sets bottom colour. A pulse tracer through the packed section should show whether that fraction is large enough to matter.
Channeling
H5114. Liquid maldistribution in structured packing is not random; it follows corrugation orientation and forms persistent high-flow lanes, so apparent HETP becomes a geometric property of how the beds were rotated at installation. Turning alternate beds by ninety degrees should change HETP without changing the packing.
Bypass
H5115. A side stripper can be bypassed by vapour rising through the draw line when the draw valve is throttled, so stripper performance is set by line static head rather than tray count. The bypass is visible as a draw temperature that tracks the main column instead of the stripper reboiler.
Dead volume
H5116. The surge volume between preheat train and flash zone accumulates a heavy heel that is periodically entrained, and that heel rather than fresh feed sets the vacuum tower’s bottom sediment. A drain-and-inspect after a sediment excursion should find the heel at the boot, not in the feed.
Heat integration constraint
H5117. Crude preheat train inlet temperature is bounded by the fouling threshold of the hottest crude-side surface, not by furnace duty, and the bound moves with crude velocity. Raising velocity raises the threshold, which is why the same train can run hotter after a throughput increase.
Mixing limitation
H5118. Desalter performance is limited by mixing-valve energy dissipation, but the response has an optimum. Too little shear leaves brine as large droplets that settle before the electric field, and too much makes submicron droplets the field cannot coalesce. The optimum should be a maximum in dehydration efficiency against valve pressure drop.
Colloidal threshold
H5119. Asphaltene precipitation in vacuum residue begins at a solvent-to-oil ratio that depends on resin fraction rather than asphaltene content alone, because resins form a peptizing shell. The threshold is a colloidal stability ratio, and two residues with the same asphaltene number can precipitate at different dilution.
Test-defined quantity
H5120. The vacuum tower’s cut point is defined by an ASTM distillation that itself cracks the residue, so the reported value depends on heating rate and flask geometry as much as on the column. A cut point quoted without its test conditions is not a column property.
Yield on the wrong basis
H5121. Vacuum gas oil yield is often reported on fresh feed, but actual recovery is reduced by gas oil entrained in the residue, so the two bases diverge as the wash section degrades. The gap between them measures wash-section entrainment and should widen before overhead colour changes.
Instrument resonance in the result
H5122. A distillation analyser’s response to a cut-point step is dominated by its own sample-line hold-up, and the apparent column lag is mostly analyser lag. A step injected at the analyser inlet, bypassing the column, should reproduce most of the observed time constant.
Existence claim
H5123. There exists a reflux ratio above which a crude tower’s fractionation cannot improve, because added liquid raises downcomer backup until the trays flood and entrainment cancels the gain. The optimum is interior rather than at maximum reflux, and it should be findable from tray pressure drop alone.
Non-uniqueness claim
H5124. The same product slate can be obtained from two different crude tower pressure profiles, so the operating point is not uniquely determined by product specifications. Energy is the tiebreaker, and a plant that fixes pressure by procedure rather than optimization is choosing one of the two arbitrarily.
Fluid catalytic cracking
Hidden competition
H5125. Gasoline olefins surviving an FCC riser are set by a competition between hydrogen transfer and cracking that depends on local coke on catalyst, not average catalyst activity. The competition should show as a maximum in olefinicity at a riser position where local coke is still low but residence time is already long.
Regime split
H5126. An FCC riser has two regimes separated by the point where feed vaporization ends and cracking begins, and the temperature minimum between them marks the boundary. The minimum’s position is set by feed droplet size, so a change in nozzle atomization should move it without changing mixed temperature.
Saturation at a geometric limit
H5127. Raising catalyst-to-oil ratio increases conversion only until the active surface is covered by a monolayer of coke precursors, after which extra catalyst circulates heat but contributes few additional sites. Saturation should appear as a flattening of conversion against circulation rate at constant riser temperature.
Optimum that does not coincide
H5128. Peak gasoline yield and peak octane occur at different catalyst-to-oil ratios, because octane is set by olefin retention while yield is set by over-cracking. A unit tuned for yield is not tuned for octane, and the two optima should be separated by a measurable interval on one circulation curve.
Two measurements of one quantity
H5129. Microactivity conversion and riser conversion disagree systematically because the fixed bed lets cracked products re-crack during a long contact while the riser’s short contact does not. The discrepancy should grow with test contact time. That growth makes the microactivity test a ranking tool rather than a scale model.
Measurement contaminating its own quantity
H5130. Coke measured on FCC catalyst by combustion includes carbon from the binder and hydrocarbon entrained in pores, and a single burn-off cannot separate them. A two-step burn at different oxygen concentrations should resolve the entrained fraction first, leaving catalytic coke as the difference.
Selectivity misread as activity
H5131. A catalyst that looks more active in a lab test may simply be more selective, preserving gasoline that a less selective catalyst would have cracked to gas. Apparent activity is then a selectivity artefact. Comparing conversion at fixed gasoline yield rather than fixed contact time should separate the two.
Recovery bias
H5132. The apparent decline of FCC gasoline octane with riser temperature in a pilot unit may be a recovery artefact, because the product train loses light olefins more completely when it is hotter. A cold trap at the reactor outlet should recover the missing olefins and restore the octane trend.
Entrainment cut
H5133. Cyclone cut size is not fixed; it shifts with gas viscosity and solids loading, so catalyst loss depends on riser outlet temperature as well as cyclone geometry. The shift should be visible as a change in the fines fraction of the catch at constant gas rate.
Threshold
H5134. A minimum riser outlet temperature should exist below which gasoline olefins lack the thermal energy for hydrogen transfer, so olefinicity rises sharply as the unit cools through that point. The threshold is chemical rather than hydraulic and should not move with catalyst circulation rate.
Hysteresis loop
H5135. Regenerator temperature and catalyst circulation rate form a hysteresis loop because the regenerator’s coke inventory and its heat release respond on different time scales. The same circulation rate can support two regenerator temperatures, depending on whether the unit is being raised or lowered in load.
Path dependence
H5136. Coke laydown in a riser depends on the feed’s droplet-size history, so two runs at the same average temperature but different atomization can produce different coke yields. That path dependence is the signature of a local rather than global reaction environment.
Conservation invariant
H5137. Hydrogen in an FCC’s products plus coke must equal hydrogen in feed plus steam, and a closure gap measures unaccounted heavy material rather than analytical noise. A hydrogen balance that closes only after the heavy oil’s assay is adjusted is hiding the gap in that assay.
Dimensional necessity
H5138. Riser mixing time is set by the ratio of diameter to gas velocity, so scale-up at constant velocity preserves mixing but not catalyst residence time. A larger riser therefore has the same mixing quality and a longer contact, changing selectivity even when the cold model is geometrically similar.
Distribution maldistribution
H5139. Spent catalyst coke distribution is bimodal because feed injection gives some particles a long contact and others a short one. Mean coke is therefore not the coke controlling the regenerator. The distribution should be recoverable by density separation, and its width should track nozzle spray quality.
False Arrhenius
H5140. Apparent activation energy of FCC cracking falls with conversion because the reaction becomes diffusion-limited inside zeolite micropores, and the curvature is a transport signature rather than a change in chemistry. A rate measured on smaller crystals should show less curvature, which is the test.
Apparent order shift
H5141. Apparent order with respect to hydrocarbon partial pressure shifts from first to half order as acid sites saturate, so a rate law fitted at one pressure fails at another. The shift should be visible as a pressure-dependent apparent rate constant in a fixed-bed test.
Interfacial film control
H5142. Gasoline sulfur is set by sulfur in the heaviest feed fraction that wets the catalyst surface, not by average feed sulfur. The interfacial film is where heavy molecules meet acid sites, and that film is the reactor. A change in feed vaporization should change product sulfur at constant conversion.
Solubility limit
H5143. Coke becomes a separate phase on catalyst only above a solubility limit in the riser vapour; below it, carbon is carried as a solute and catalyst colour is not a measure of coke. The limit should move with vapour aromatic content, which is why a more aromatic feed darkens catalyst at constant coke.
Thermodynamic inconsistency
H5144. A cracking yield pattern reporting more aromatics than the feed’s hydrogen balance allows is thermodynamically inconsistent, and the excess suggests product analysis has assigned cyclic structures to olefins. A hydrogen-to-carbon check on the whole product slate should catch the misassignment before the yield is used for economics.
Kinetic constraint
H5145. Maximum gasoline yield in a riser is bounded by hydrogen-transfer kinetics rather than cracking equilibrium, so the bound moves with the catalyst’s hydrogen-transfer activity. A catalyst with more such sites should raise the bound without changing equilibrium.
Pressure drop diagnostic
H5146. Riser pressure drop is not only hydraulic; its deviation from the expected two-phase gradient measures catalyst inventory and therefore circulation rate. Calibrating pressure drop against a known circulation rate should make inventory observable without a tracer.
Recycle accumulation
H5147. Recycling heavy cycle oil accumulates polynuclear aromatics that crack slowly and deposit on catalyst, so the recycle’s true effect is higher coke yield at constant conversion. Accumulation should appear as a gradual rise in coke yield after a recycle change, with a time constant set by unit inventory.
Non-existence claim
H5148. No single equilibrium-catalyst activity characterizes an FCC unit, because the circulating inventory’s activity is a distribution and any single number is a moment that does not predict response to a feed change. Activity and hydrogen-transfer selectivity together are the minimum two-parameter description.
Coincidence of two transitions
H5149. Transitions between dilute and dense-phase flow in a riser coincide with the choking point, so a change in solids flux can move the riser between regimes without any change in catalyst. That coincidence means an apparent catalyst effect can be a hydrodynamic effect in disguise.
Hydrotreating and hydroprocessing
Hidden variable
H5150. Hydrodesulfurization rate in a trickle bed is set by liquid wetting efficiency, which depends on the bed’s pre-wetting history rather than intrinsic activity. A bed wetted under vacuum should outperform one wetted by gradual fill at the same conditions, and the difference should vanish at high liquid velocity.
Ratio-defined threshold
H5151. Below a minimum hydrogen partial pressure HDS stops following normal kinetics because the surface becomes sulfur-rich, and the threshold is set by the H2S-to-H2 ratio rather than pressure alone. A high-pressure unit with high H2S should behave like a low-pressure unit.
Sign flip with catalyst family
H5152. Adding H2S can promote HDS on a CoMo catalyst and inhibit it on a NiMo catalyst, so the sign of the effect diagnoses the active phase. The flip should appear as a change in apparent reaction order when one feed is run over both.
Diffusion-length distribution
H5153. Apparent first-order HDS kinetics may be the signature of a distribution of particle sizes with different diffusion lengths, not a single surface reaction. A bed screened into two narrow fractions should give two apparent rate constants. Their ratio should be set by the diffusion length.
Transport bound
H5154. Maximum HDN conversion in a trickle bed is bounded by diffusion of nitrogen compounds into micropores, not by intrinsic HDN rate. The bound should rise with temperature more steeply than the intrinsic rate, because diffusion and reaction have different activation energies.
Decoupling of two rates
H5155. HDN and HDS rates can be decoupled by changing liquid hourly space velocity, because HDN is more diffusion-limited at high pressure while HDS is more surface-limited. Plots of the two conversions against space velocity should cross at a point identifying the transport regime.
Packing confound
H5156. The apparent improvement in HDS with smaller particles may be a packing confound rather than shorter diffusion paths. A test at constant void fraction and bed density should separate the two.
Flow-weighted mean
H5157. Product sulfur is a flow-weighted mean over the reactor’s residence-time distribution, so the same mean can come from a narrow distribution with a high outlet or a broad one with a low outlet. A tracer test is needed to know which, and the distinction matters when the specification sits near the mean.
Additivity failure
H5158. Hydrogen consumption is not the sum of a desulfurization term and an aromatic-saturation term, because the two reactions compete for the same hydrogen and sites. A model that adds the two pure-feed terms should overpredict at high severity, where competition is strongest.
Thermodynamic constraint
H5159. Aromatic saturation is equilibrium-limited at high temperature, so hydrogen consumption for a given cetane gain has a maximum at intermediate temperature. Above that point, added severity destroys cetane by dehydrogenating the naphthenes it just made.
Coupled-coverage rate law
H5160. The HDS rate’s pressure dependence is not a simple power law because hydrogen and sulfur species compete for the same sites, and their coverages are coupled through a Langmuir-Hinshelwood balance. A single power law fitted at one H2S level will mispredict the pressure response at another.
Phase equilibrium misassignment
H5161. Hydrogen solubility in a liquid feed is usually computed from an equation of state, but at high pressure the liquid is saturated. Solubility is then set by gas fugacity rather than Henry’s law. The misassignment appears as a hydrogen balance that closes only when solubility is fitted, a warning that the model is absorbing the error.
Lumping error
H5162. Lumping diesel into a few pseudocomponents hides the refractory sulfur species that set final sulfur, so a model calibrated on the lumped feed overpredicts achievable desulfurization. Spiking the feed with a known refractory species should expose the gap without changing lumped properties.
Test-rate dependence
H5163. Cloud point is defined by a standard test whose cooling rate sets wax crystal size, so the reported value is a kinetic measurement rather than an equilibrium one. Two laboratories using different cooling rates can disagree on the same sample without either being wrong.
Blending antagonism
H5164. Cloud point of a hydrotreated diesel blended with light kerosene is not linear, because kerosene dissolves wax nuclei and suppresses crystallization. The blend’s cloud point can be lower than either component’s, making the linear blending rule conservative in the wrong direction.
Film-thickness control
H5165. At low temperature the HDS rate is controlled by hydrogen mass transfer through the liquid film on catalyst, and film thickness is set by liquid velocity rather than activity. A velocity increase at constant space velocity should raise conversion until film resistance disappears.
Wall-flow bypass
H5166. In a trickle bed the liquid channels along the wall because the wall region has higher void fraction, so performance is partly set by a bypass rather than by the bulk bed. A wall-coated bed with the same bulk packing should show lower conversion, with the difference scaling as diameter-to-particle ratio.
State multiplicity
H5167. Catalyst sulfidation state and reactor H2S concentration can support two stable states at one operating point. A more sulfided surface produces more H2S, and a less sulfided one produces less. The multiplicity should appear as hysteresis in conversion when H2S is cycled.
Purge-rate control
H5168. Recycle gas hydrogen purity is set by accumulation of methane and light hydrocarbons that the amine unit cannot remove, so apparent hydrogen partial pressure depends on purge rate rather than makeup hydrogen. Raising makeup to compensate for low purity treats a symptom of insufficient purging.
Exchanger limit
H5169. Maximum hydrotreater inlet temperature is bounded by feed-effluent exchanger fouling resistance, not catalyst activity, so a unit called temperature-limited may be exchanger-limited. A rising exchanger approach temperature should precede the loss of conversion.
Stagnant-volume retention
H5170. Liquid residence time in a trickle bed is not a single plug-flow value; a stagnant fraction can hold sulfur-rich material that desorbs later and contaminates product. A step change in feed sulfur should produce a long, low-amplitude response if that volume is significant.
Saturation of a promoter
H5171. Above some hydrogen partial pressure further increases do not improve HDS because the surface is saturated with hydrogen and the rate becomes zero-order. The saturation point should be a knee in the conversion-pressure curve, and it should move with temperature.
Scale-up invariant
H5172. Reactor pressure drop is set by the ratio of particle diameter to column diameter, so scale-up at constant ratio preserves pressure drop per unit length but not total pressure drop. A commercial reactor is therefore hydraulically similar to the pilot unit. It is thermally dissimilar, which is where scale-up error enters.
Delayed coking
Unconverted-fraction term
H5173. Delayed coker coke yield contains a term from recycle heavy material that is not converted but deposited. Yield against recycle ratio therefore measures that deposit rather than the feed’s coke-forming tendency. A zero-recycle run should give the true feed yield, and the difference should scale with recycle Conradson carbon.
Misattribution
H5174. The shot-coke versus sponge-coke transition is usually attributed to feed asphaltene content, but it may be controlled by drum fill rate and foam stability. A feed that makes sponge coke at slow fill should make shot coke at fast fill if the attribution is wrong.
Foam-collapse limit
H5175. A minimum drum vapour velocity should exist below which foam does not collapse, and collapse is a prerequisite for a clean coke cut. A drum run below that velocity should show a ragged coke surface and higher volatile content at the top.
Reversal
H5176. Raising furnace outlet temperature can either raise or lower coke yield depending on whether added heat drives cracking or vaporization. The sign is set by feed Conradson carbon. A high-carbon feed should lose yield with temperature while a low-carbon feed gains it, a testable crossover.
Sampling-position bias
H5177. Apparent improvement of coke quality with drum size may be a sampling-position bias, because drum top and bottom have different volatile contents. A depth-resolved sampling program should reproduce the trend within a single drum.
Stoichiometric bound
H5178. Maximum liquid yield from a coker is bounded by feed hydrogen content, not furnace temperature, and a yield above that bound signals over-vaporized and recondensed product. The bound can be estimated from the feed’s hydrogen-to-carbon ratio and should be checked before any yield claim is believed.
Solubility-parameter criterion
H5179. Onset of coke formation in furnace tubes is a colloidal threshold set by asphaltene solubility parameter, not by skin temperature alone. A feed whose asphaltenes sit near their solubility limit should coke at lower skin temperature than one with the same Conradson carbon but more resins.
Hydrogen-balance inconsistency
H5180. A coker gas composition with more hydrogen than the feed balance allows is inconsistent, and the excess indicates entrained light hydrocarbons. A gas chromatograph with heavy-hydrocarbon backflush should resolve the entrainment and close the balance.
Precursor diagnostic
H5181. Furnace tube pressure drop rises before skin temperature does, because coke laydown first narrows flow area and only later insulates the tube. Pressure drop is therefore the earlier diagnostic, and control that waits for skin temperature is already late.
Thermal-lag loop
H5182. Quench water rate and coke volatile content form a loop because the coke surface cools faster than its interior, so one quench rate can leave two volatile contents depending on history. A step change in quench rate should show a response with the drum’s internal diffusion time constant.
Profile non-uniformity
H5183. The coke drum’s temperature profile is not uniform, and the centre cools more slowly than the wall. Quench-complete time is therefore set by the centre rather than the average. A wall-mounted thermocouple will declare completion too early, and the error should grow with drum diameter.
Diffusion-limited activation energy
H5184. Coke formation’s apparent activation energy falls with residence time because the reaction becomes diffusion-limited in the coke layer. A tube with a thinner initial layer should show a higher apparent activation energy. That difference is the test.
Non-monotone response
H5185. Coke hardness rises with drum pressure and then falls, because higher pressure increases density but also traps more volatile material in pores. Maximum hardness should sit at intermediate pressure. It should be findable by cutting drums run at different pressures.
Method disagreement
H5186. Volatile matter by proximate analysis and volatile content inferred from drum off-gas disagree because proximate analysis includes surface moisture. Vacuum-drying the sample before testing should close the gap, and the residual difference is the true analytical bias.
Optimal fill fraction
H5187. An optimal drum fill fraction exists above which the coke top surface sits too close to the vapour outlet, so foam carryover rises and coke quality falls. The optimum should be a maximum in clean-cut fraction against fill level and should move with feed foam tendency.
Refractory accumulation
H5188. Recycling heavy gas oil accumulates refractory aromatic species that crack slowly, so recycle raises coke yield at constant conversion. Accumulation should appear as a slow rise in coke yield after a recycle change, with a time constant set by drum cycle.
Corrosion in process units
Reachability limitation
H5189. Naphthenic acid corrosion rate is set by the acid’s ability to reach metal, which depends on oil viscosity and flow regime rather than total acid number alone. A high-acid, high-viscosity feed can corrode less than a lower-acid, low-viscosity one at the same temperature.
Shear-stress limit
H5190. A minimum wall shear stress should exist below which naphthenic acid corrosion stops, because the product film is not removed and acid must diffuse through it. The threshold is hydrodynamic and should be reachable by raising velocity at constant temperature and acid number.
Temperature inversion
H5191. Increasing crude sulfur can reduce naphthenic acid corrosion at low temperature and increase it at high temperature, because the sulfide film protects only below a transition temperature. The inversion should appear as a crossing of two corrosion-rate curves. Two crudes with different sulfur levels should show that crossing when their rates are plotted against temperature.
Corrodent misattribution
H5192. Overhead corrosion is usually attributed to hydrogen chloride, but it may be controlled by ammonium bisulfide concentration and water pH, which together set the dew point. A unit that removes chloride but not ammonia should still corrode when bisulfide is high enough.
Probe-mounting artefact
H5193. Corrosion rate from an electrical-resistance probe can be a probe-mounting artefact, because the probe’s temperature differs from the pipe wall’s when its mounting conducts heat away. An insulated probe should report a different rate, and the difference is the artefact.
Phase-change bound
H5194. Maximum corrosion rate in a distillation column is bounded by dew-point location rather than acid concentration, because above the dew point no aqueous phase exists and the rate collapses. Moving the dew point by changing top pressure can change the corrosion pattern without changing chemistry.
Two mechanisms separated
H5195. Sulfidation and naphthenic acid corrosion can be separated by velocity dependence, because sulfidation is diffusion-limited and velocity-sensitive while acid corrosion is surface-limited and less sensitive. A velocity sweep at constant temperature should show two slopes. The slopes identify the dominant mechanism.
Film-history effect
H5196. Protectiveness of a corrosion product film depends on its formation history, so a surface that formed its film at low velocity is not protected at that same velocity after a high-velocity excursion. Film history, not current thickness, is the state variable.
Iron-balance closure
H5197. Total iron in a unit’s effluent must equal iron removed from the walls, and a closure gap measures corrosion in unmonitored locations rather than analytical loss. A unit that closes its iron balance to within an estimate of ten percent can still hide a local rate that is much higher.
Scale-mechanism transition
H5198. Sulfidation rate’s temperature dependence changes at the steel’s tempering temperature because scale growth switches from outward cation diffusion to inward anion diffusion. The change should appear as a break in the Arrhenius plot, and the break temperature should depend on chromium content.
Protective-film maximum
H5199. Corrosion rate in a sour environment rises with hydrogen sulfide partial pressure and then falls as the sulfide film thickens and becomes more protective. The maximum should sit at intermediate partial pressure. Its position should move with temperature and flow.
Critical-velocity existence
H5200. A critical flow velocity should exist above which the corrosion product film is removed and the rate becomes independent of oxygen content, because metal dissolution then controls. The critical velocity should be a knee in the rate-velocity curve. It should also scale with the square root of pipe diameter.
Status and plan
One hundred entries, numbered in sequence. Each was written on its own, with the argument shape chosen before the subject, so that no two share a form; the label above each claim is there to be checked against the sentence beneath it rather than accepted as a taxonomy.
The physics stays inside the process: the tray that weeps, the riser that chokes, the trickle bed that bypasses at the wall, the drum that cools from the skin inward, and the probe whose own temperature is part of the rate it reports. Nothing here depends on a vendor’s catalyst name or on a plant’s operating record.
If one of these is worth an afternoon, it is H5103 — that added reflux can worsen a crude tower’s split once the trays weep, because the hydraulic limit arrives before the fractionation limit. It needs one column, two reflux levels, and a tray pressure drop.
Incoprea Research · hand-considered hypotheses 5101–5200 · 3 November 2026 · ~/Desktop/Nov3/