Fundamentals of Inhibitors

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FUNDAMENTALSFUNDAMENTALS

OF INHIBITORSOF INHIBITORS

1 AV Santos & Associates : August 2010 :


InhibitorsInhibitors

An Inhibitor is a substance which retards or An Inhibitor is a substance which retards or. .

A Corrosion inhibitor is a substance which, when A Corrosion inhibitor is a substance which, whenadded to an environment, decreases the rate ofadded to an environment, decreases the rate ofattack by the environment on a metal.attack by the environment on a metal.

Corrosion inhibitors are commonly added inCorrosion inhibitors are commonly added in

, ,, ,and other environment, either continuously orand other environment, either continuously orintermittently to prevent serious corrosion.intermittently to prevent serious corrosion.






CORROSION INHIBITORSCORROSION INHIBITORS



Points of view of CorrosionPoints of view of Corrosioninhibitorsinhibitors

Their effects on the corrosion process.Their effects on the corrosion process.

Their interactions with various aggressiveTheir interactions with various aggressiveenvironments.environments.

Properties of the inhibitors themselvesProperties of the inhibitors themselves

Possible effects of inhibitors on unitPossible effects of inhibitors on unit

..






INHIBITORS AND THEINHIBITORS AND THE

ENVIRONMENTENVIRONMENT Aqueous Systems Aqueous Systems

--corrosion inhibitors are applied.corrosion inhibitors are applied.

-- Water is a powerful solvent capable of carrying manyWater is a powerful solvent capable of carrying manydifferent ions at the same time.different ions at the same time.

-- The main factor which must be considered in theThe main factor which must be considered in theapplication of corrosion inhibitors to aqueous systemsapplication of corrosion inhibitors to aqueous systemsare salt concentration, pH, dissolved oxygenare salt concentration, pH, dissolved oxygenconcen ra on an e concen ra on o n er er ngconcen ra on an e concen ra on o n er er ngspecies.species.



AQUEOUS SYSTEM AQUEOUS SYSTEM






Common Dissolved Substances and theirCommon Dissolved Substances and their

effects on corrosion inhibitorseffects on corrosion inhibitors Oxygen (O2)Oxygen (O2) – – in neutral water, oxygen causes corrosion, if it isin neutral water, oxygen causes corrosion, if it is

reduced to less than 0.1 ppm by scavenging compounds or byreduced to less than 0.1 ppm by scavenging compounds or by,,

system. Oxygen can be utilized in passivating steel by adding asystem. Oxygen can be utilized in passivating steel by adding apassivating inhibitors. Organic inhibitors are seldom effectivepassivating inhibitors. Organic inhibitors are seldom effectiveagainst oxygenagainst oxygen--caused attack unless they contain passivatingcaused attack unless they contain passivatinggroups such as benzoate or nitrite.groups such as benzoate or nitrite.

Chloride (Cl)Chloride (Cl) – – Steel is more difficult to passivate in the presenceSteel is more difficult to passivate in the presenceof the chloride ion, therefore a higher concentration of passivatingof the chloride ion, therefore a higher concentration of passivatinginhibitors is required if Cl are present. Also chloride ions areinhibitors is required if Cl are present. Also chloride ions ares rong y a sor e y s ee .s rong y a sor e y s ee .

Sulfate (SO)Sulfate (SO) – – The effect of sulfate on passivity are similar toThe effect of sulfate on passivity are similar tothose of chloride but to a lesser degree, sulfates or chlorides mustthose of chloride but to a lesser degree, sulfates or chlorides mustnot be allowed to build up in a system by evaporating becausenot be allowed to build up in a system by evaporating becausedepassivation may occur.depassivation may occur.



Bicarbonate (HCO3) – bicarbonate in hard waters can be utilized for naturalinhibition. If soft waters, corrosion inhibitors must be used if excess carbondioxide is present because of the acidic condition it produces.

Sulfides (S-) – Sulfides precipitate many metal ions. For example, inhibitorswhich contain zinc cannot be used. Oxidizing inhibitors are reduced by sulfide to

.precipitate of free sulfur can be tolerated.

Metal Cations – Sodium (Na) and Potassium (K) ions have no particular effectson inhibitors; Calcium (Ca) and Magnesium (Mg) may be used to form protectiveprecipitates but at high concentrations they interfere with inhibition byprecipitating non-protective deposits and also by precipitating inhibitors such asphosphate (PO4) and Silicate (SiO3).

Acid (H+) – hydrogen ion increase corrosion rates and increase the difficulty of

passivating steel. Passivation is used in sulfuric (H2SO4) and phosphoric acid(H3PO4) but not in hydrochloric acid (HCI). Non-passivating organic or cathodicinhibitors are preferred in pickling acids to avoid the disastrous consequences ofdepassivation.

Alkali (OH-) In alkaline solutions, corrosion of steel is controlled by the rate ofoxygen diffusion through the precipitated corrosion products so corrosion ratesare low. Steel is easily passivated in alkaline solutions.






WATER OF LOWWATER OF LOW— —TOTO--MODERATEMODERATE

SALT CONCENTRATIONSALT CONCENTRATION

Water of lowWater of low--toto--moderate salt concentrations aremoderate salt concentrations areencountered in munici al water s stems, coolin waters,encountered in munici al water s stems, coolin waters,marine and offshore activities and oilfield water injectionmarine and offshore activities and oilfield water injectionsystem.system.

In closed reIn closed re--circulating system, oxygen can be excludedcirculating system, oxygen can be excludedand corrosion often can be controlled by adjusting theand corrosion often can be controlled by adjusting thepH to an alkaline value.pH to an alkaline value.

In open systems corrosion is more severe and goodIn open systems corrosion is more severe and good

dissolved salts in water, an inhibitor has more difficultydissolved salts in water, an inhibitor has more difficulty

in reaching the metal surface and displacing absorbedin reaching the metal surface and displacing absorbedion than it has in demineralized water, hence a higherion than it has in demineralized water, hence a higherconcentration of inhibitor is required.concentration of inhibitor is required.



Cooling water systems may be either recirculating orCooling water systems may be either recirculating oronceonce--through types.through types.

Recirculating systems are more easily controlled byRecirculating systems are more easily controlled byin i itors since ig er concentrations can e app iein i itors since ig er concentrations can e app iebecause the water is reused.because the water is reused.

Sodium chromate or sodium nitrite are both effectiveSodium chromate or sodium nitrite are both effectivealloy steel closed recirculating system.alloy steel closed recirculating system.

Sodium nitrite may form ammonia by reduction atSodium nitrite may form ammonia by reduction atcathodic sites, therefore it should not be used in systemscathodic sites, therefore it should not be used in systems

which include brass or copper since these materials arewhich include brass or copper since these materials aresubject to stress corrosion cracking by ammonia.subject to stress corrosion cracking by ammonia.






HIGH SALT CONCENTRATIONSHIGH SALT CONCENTRATIONS

Extremely high salt concentrations are used in aqueousExtremely high salt concentrations are used in aqueous

temperatures encountered are always low and since thetemperatures encountered are always low and since thebrines are recirculated, a high concentration of inhibitorbrines are recirculated, a high concentration of inhibitorcan be maintained economically.can be maintained economically.

Sodium Chromate is effective in refrigeration brinesSodium Chromate is effective in refrigeration brinesprovided there is no limitation due to its toxicity. Ifprovided there is no limitation due to its toxicity. Ifh siolo ical effects are a factor then disodiumh siolo ical effects are a factor then disodium

phosphate can be used although it is not as effective asphosphate can be used although it is not as effective as

sodium chromate in controlling corrosion.sodium chromate in controlling corrosion.



Effects of pHEffects of pH

The pH of aqueous solutions is extremely important inThe pH of aqueous solutions is extremely important in

effective and most economical. Natural hard waterseffective and most economical. Natural hard watersretain compounds of calcium in solution because of theretain compounds of calcium in solution because of theequilibrium.equilibrium.

At high temperatures the reverse reaction occurs and At high temperatures the reverse reaction occurs andheated surfaces become coated with CaCO3. Aheated surfaces become coated with CaCO3. A

becomes alkaline in the region of cathodic areas.becomes alkaline in the region of cathodic areas.






Gaseous EnvironmentGaseous Environment

Gaseous environments include the openGaseous environments include the opena mosp ere, e vapor p ase n an s,a mosp ere, e vapor p ase n an s,natural gas in walls and the empty spacenatural gas in walls and the empty spacein packaging containers. Water andin packaging containers. Water andoxygen are the principal corrosive agentsoxygen are the principal corrosive agentsbut the main problem in providingbut the main problem in providinginhibitors is to transport the inhibitorsinhibitors is to transport the inhibitors

from a source to the sites where corrosionfrom a source to the sites where corrosionmay occur.may occur.



The Open AtmosphereThe Open Atmosphere

It is applied directly to the metal surfaces to beIt is applied directly to the metal surfaces to bepro ec e .pro ec e .

The most common method is the use ofThe most common method is the use ofchromates in paints. Zinc chromate and red leadchromates in paints. Zinc chromate and red leadare used in primer coats.are used in primer coats.

Volatile inhibitors are never used in the open Volatile inhibitors are never used in the openatmos here because the are im ractical andatmos here because the are im ractical and cannot saturate the vapor space.cannot saturate the vapor space.






Closed Vapor SpacesClosed Vapor Spaces

The walls of tanks above a water line are subject toThe walls of tanks above a water line are subject to

always high and oxygen is plentiful if the tank is ventedalways high and oxygen is plentiful if the tank is ventedto the atmosphere.to the atmosphere.

An oil layer containing about 15% lanolin is used in ship An oil layer containing about 15% lanolin is used in shipballast tanks to control corrosion.ballast tanks to control corrosion.

A layer of oil on the surface helps to maintain a low A layer of oil on the surface helps to maintain a low

are coated with a layer of oil. The oil may contain anare coated with a layer of oil. The oil may contain an

organic inhibitor and an agent usually amine to causeorganic inhibitor and an agent usually amine to causethe oil to spread on the metal surface.the oil to spread on the metal surface.



Effects of Elevated TemperatureEffects of Elevated Temperature

Most effects of elevated temperature are adverse toMost effects of elevated temperature are adverse to

High temperatures increase corrosion rates (aboutHigh temperatures increase corrosion rates (aboutdouble for a 20F rise at a room temperature) and theydouble for a 20F rise at a room temperature) and theydecrease the tendency of inhibitors to absorb on metaldecrease the tendency of inhibitors to absorb on metalsurfaces.surfaces.

PrecipitatePrecipitate--forming inhibitors are less effective atforming inhibitors are less effective at

of the protective deposit.of the protective deposit.

Thermal stability of corrosion inhibitors is an importantThermal stability of corrosion inhibitors is an importantconsideration at high temperature.consideration at high temperature.






Types of InhibitorsTypes of Inhibitors

Passivating InhibitorsPassivating Inhibitors

Passivating inhibitors are the most effective ofPassivating inhibitors are the most effective ofall inhibitors because they are stifle corrosion almostall inhibitors because they are stifle corrosion almostcompletely. They also known as dangerous inhibitorscompletely. They also known as dangerous inhibitorsbecause under certain conditions they can acceleratesbecause under certain conditions they can acceleratescorrosion.corrosion.

There are two types of passivating inhibitors: OxidizingThere are two types of passivating inhibitors: Oxidizing

steel in the absence of oxygen and the nonsteel in the absence of oxygen and the non--oxidizingoxidizing

ions such as phosphate, tungsten, moluoions such as phosphate, tungsten, moluo--date whichdate whichrequire the presence of oxygen to passivate steel.require the presence of oxygen to passivate steel.



Cathodic InhibitorsCathodic Inhibitors

Inhibition by polarization of the cathodic reaction can beInhibition by polarization of the cathodic reaction can be

have been given. The three main categories of inhibitorshave been given. The three main categories of inhibitorswhich affect the cathode reaction are cathode poisons,which affect the cathode reaction are cathode poisons,cathode precipitates and scavengers.cathode precipitates and scavengers.

Cathode PoisonCathode Poison – – is the formation of hydrogen atoms oris the formation of hydrogen atoms orrecombination of hydrogen atoms to hydrogen gas onrecombination of hydrogen atoms to hydrogen gas onthe surface of the corrodin metal. The rate of thethe surface of the corrodin metal. The rate of the

cathode reaction is showed and because anodic andcathode reaction is showed and because anodic andcathodic reactions must proceed as the same rate, thencathodic reactions must proceed as the same rate, thenthe whole corrosion process is slowed.the whole corrosion process is slowed.






Cathode PrecipitatesCathode Precipitates

The most widely used cathodic precipitation typeThe most widely used cathodic precipitation type

because they occur in natural waters inhibition withbecause they occur in natural waters inhibition withthem usually requires only an adjustment of pH.them usually requires only an adjustment of pH.

Many natural waters and municipal water suppliesMany natural waters and municipal water suppliescontain calcium carbonate (limestone) in solution.contain calcium carbonate (limestone) in solution.Limestone is dissolved in water by reaction to formLimestone is dissolved in water by reaction to formsoluble calcium bicarbonate. Limestone can be caused tosoluble calcium bicarbonate. Limestone can be caused to precipitates again, forming a milky white suspension byprecipitates again, forming a milky white suspension by

making the calcium bicarbonate solution more alkalinemaking the calcium bicarbonate solution more alkalineby adding more calcium ions.by adding more calcium ions.



Organic InhibitorsOrganic Inhibitors

Organic compounds constitute a broad class of corrosionOrganic compounds constitute a broad class of corrosion

cathodic or anodic.cathodic or anodic.

Cathodic or anodic effects alone are sometimes observedCathodic or anodic effects alone are sometimes observedin the presence of organic inhibitors. They affect thein the presence of organic inhibitors. They affect theentire surface of a corroding metal when present inentire surface of a corroding metal when present insufficient concentration.sufficient concentration.

degrees depending on potential of the metal, chemicaldegrees depending on potential of the metal, chemicalstructure of the inhibitor and size of the molecule.structure of the inhibitor and size of the molecule.






Oxygen Scavenger Oxygen Scavenger

Corrosion of steel in water above pH 6.0 is due to theCorrosion of steel in water above pH 6.0 is due to the

cathodic reaction.cathodic reaction.

Oxygen scavengers are added to water either alone orOxygen scavengers are added to water either alone orwith a corrosion inhibitor to retard corrosion.with a corrosion inhibitor to retard corrosion.

Organic corrosion inhibitors alone in the generated brineOrganic corrosion inhibitors alone in the generated brinewater will slow general corrosion, but will not alwayswater will slow general corrosion, but will not always

. .

The most common oxygen scavengers used in water atThe most common oxygen scavengers used in water at

ambient temperature are sodium sulfite and sulfurambient temperature are sodium sulfite and sulfurdioxide.dioxide.



Precipitation Inhibitor Precipitation Inhibitor

These are filmThese are film--forming compounds whose action isforming compounds whose action iseneral over the metal surface and interfere with botheneral over the metal surface and interfere with both

anodes and cathodes in directly.anodes and cathodes in directly.

The most common inhibitors of this class are the silicatesThe most common inhibitors of this class are the silicatesand phosphates.and phosphates.

In nearIn near--neutral waters containing a low concentration ofneutral waters containing a low concentration ofchlorides, silicates and phosphates cause passivation ofchlorides, silicates and phosphates cause passivation ofsteel when oxygen are present but they behave assteel when oxygen are present but they behave as

.. Corrosion is localized in the form of pitting whenCorrosion is localized in the form of pitting when

insufficient amounts of phosphate or silicate are addedinsufficient amounts of phosphate or silicate are addedto saline water.to saline water.






Vapor Phase InhibitorsVapor Phase Inhibitors

Vapor Phase Inhibitors (VPI) are compounds which are transported Vapor Phase Inhibitors (VPI) are compounds which are transportedin a closed system to the site of corrosion by volatilization from ain a closed system to the site of corrosion by volatilization from asource.source.

In boilers, volatile basic compounds such as morpholine or ethyleneIn boilers, volatile basic compounds such as morpholine or ethylene--diamine are transported with steam to prevent corrosion indiamine are transported with steam to prevent corrosion incondenser tubes by neutralizing acidic carbon dioxide.condenser tubes by neutralizing acidic carbon dioxide.

Compounds of this type inhibit corrosion by making the environmentCompounds of this type inhibit corrosion by making the environmentalkaline.alkaline.

In closed vapor spaces, such as shipping containers, volatile solidsIn closed vapor spaces, such as shipping containers, volatile solidssuch as the nitrite, carbonate and benzoate salt ofsuch as the nitrite, carbonate and benzoate salt ofdicyclohexylamine, cyclohexylamine and hexqmethylene are used.dicyclohexylamine, cyclohexylamine and hexqmethylene are used.

The mechanism of inhibition by these compounds is not entirelyThe mechanism of inhibition by these compounds is not entirely

clear, but is appear certain that the organic portion of the moleculesclear, but is appear certain that the organic portion of the moleculesmerely provides volatility.merely provides volatility.



Application of Inhibitors Application of Inhibitors Concentration and Performance TerminologyConcentration and Performance Terminology

-- Corrosion inhibitors are sold in solid or liquid form. Most solids areCorrosion inhibitors are sold in solid or liquid form. Most solids arere ative y pure ut sometimes a so i in i itor is use wit anot erre ative y pure ut sometimes a so i in i itor is use wit anot eringredient or incapsulated where a controlled rate of solubility isingredient or incapsulated where a controlled rate of solubility isrequired.required.

-- Liquids are usually preferred because of the ease with which theyLiquids are usually preferred because of the ease with which theycan be transported , measured and dispersed.can be transported , measured and dispersed.

-- ,,freezing or boiling point, they are dissolved in an appropriatefreezing or boiling point, they are dissolved in an appropriatesolvent to achieve the properties desired. It is also often desirablesolvent to achieve the properties desired. It is also often desirableto blend the inhibitor with a demulsifier, dispersant, surfactant, antito blend the inhibitor with a demulsifier, dispersant, surfactant, anti--foaming agent of synergetic agent.foaming agent of synergetic agent.






-- Liquid inhibitors are solid by the gallon, part of which is solvent. TheLiquid inhibitors are solid by the gallon, part of which is solvent. The

amount of inhibitor present is expressed as “percent active”. Aamount of inhibitor present is expressed as “percent active”. Agallon of inhibitor which is 20 percent by weight of inhibitor. In coldgallon of inhibitor which is 20 percent by weight of inhibitor. In coldclimates where inhibitors are likely to be stored or used in subclimates where inhibitors are likely to be stored or used in subreezing temperatures.reezing temperatures.

-- It may be impossible to use as concentrated a solution as in warmerIt may be impossible to use as concentrated a solution as in warmerclimates without resorting to more expensive solvents.climates without resorting to more expensive solvents.

-- Corrosion inhibitors are usually compared on the basis of theirCorrosion inhibitors are usually compared on the basis of theirinhibitor efficienc which is the ercenta e that corrosion is loweredinhibitor efficienc which is the ercenta e that corrosion is loweredin their presence as compared to the corrosion rate which occurs inin their presence as compared to the corrosion rate which occurs intheir absence.their absence.



The inhibitor efficiency is calculated from the formula:The inhibitor efficiency is calculated from the formula:

R0R0 – – R1R1

E = x 100E = x 100

R0R0

Where: E = inhibitor efficiencWhere: E = inhibitor efficienc

R0 = corrosion rate in the absence of inhibitorR0 = corrosion rate in the absence of inhibitor

R1 = corrosion rate in the presence of inhibitorR1 = corrosion rate in the presence of inhibitor






Application Techniques Application Techniques

Continuous InjectionContinuous Injection

-- This method is used for water supplies, oil fieldThis method is used for water supplies, oil fieldinjection water, onceinjection water, once--through cooling water, openthrough cooling water, openannulus oil or gas wells and gasannulus oil or gas wells and gas--lift wells.lift wells.

-- Liquid inhibitors are injected with a chemical injectionLiquid inhibitors are injected with a chemical injectionpump, these pumps are extremely reliable and requirepump, these pumps are extremely reliable and requirelittle maintenance. Most chemical injection pumps can belittle maintenance. Most chemical injection pumps can be

adjusted to deliver at the desired injection rate.adjusted to deliver at the desired injection rate.



-- Another form of continuous application is by the use of Another form of continuous application is by the use ofslightlyslightly--soluble forms of solid inhibitors. The inhibitorsoluble forms of solid inhibitors. The inhibitorsuch as glassy phosphate or silicate in the form of asuch as glassy phosphate or silicate in the form of acartri ge is continuous y reac e out y t e passage ocartri ge is continuous y reac e out y t e passage ofluid through the cartridge.fluid through the cartridge.

-- Inhibitors in the form of sticks or pellets are used in oilInhibitors in the form of sticks or pellets are used in oiland gas wells to supply inhibitor continuously by theirand gas wells to supply inhibitor continuously by theirnatural slow dissolution.natural slow dissolution.






Batch TreatmentBatch Treatment

-- The most familiar example of batch treatment is the automobileThe most familiar example of batch treatment is the automobilecooling system. A quantity of inhibitor is added at one time tocooling system. A quantity of inhibitor is added at one time toprovide protection for an extended period. Additional inhibitor mayprovide protection for an extended period. Additional inhibitor maybe added periodically or the fluid may be drained and replaced withbe added periodically or the fluid may be drained and replaced witha new supply.a new supply.

-- Closed loop, cooling systems it is important that the inhibitorClosed loop, cooling systems it is important that the inhibitorconcentration be measured occasionally to insure that a safe level isconcentration be measured occasionally to insure that a safe level ismaintained.maintained.

-- It is also used in treating oil and gas wells. An inhibitor is delutedIt is also used in treating oil and gas wells. An inhibitor is delutedwith an appropriate solvent and injected into the annulus of openwith an appropriate solvent and injected into the annulus of open--hole wells or into the tubin of as wells that have a acker.hole wells or into the tubin of as wells that have a acker.

-- In this application it is important that the inhibitor contact allIn this application it is important that the inhibitor contact allsurfaces and that it has a good persistence. Most wells requiresurfaces and that it has a good persistence. Most wells requirebatch treatment about every two weeks.batch treatment about every two weeks.



BATCH TREATMENTBATCH TREATMENT






Squeeze TreatmentSqueeze Treatment

-- It is a method of continuously feeding inhibitor into anIt is a method of continuously feeding inhibitor into anoil well.oil well.

-- A quantity of inhibitor is pumped into a well and is A quantity of inhibitor is pumped into a well and isfollowed by sufficient solvent to force the inhibitor tofollowed by sufficient solvent to force the inhibitor toabsorbed by the formation from which it slowly escapesabsorbed by the formation from which it slowly escapesto inhibit the produced liquid.to inhibit the produced liquid.

-- The rotection a lied in this manner has been knownThe rotection a lied in this manner has been knownto last for a year.to last for a year.



Volatilization Volatilization

-- It is also connected to boilers and closed container. It is also theIt is also connected to boilers and closed container. It is also theinhibition of gas condensate corrosion.inhibition of gas condensate corrosion.

-- This treatment is also the same as used in batch and squeezeThis treatment is also the same as used in batch and squeezetreatment.treatment.

CoatingCoating-- Inhibitors are used in coatings exposed to the open atmosphere.Inhibitors are used in coatings exposed to the open atmosphere.

-- When moisture contacts the paint, some inhibitor is leached out toWhen moisture contacts the paint, some inhibitor is leached out toprotect the metal. The inhibitor must be soluble enough to beprotect the metal. The inhibitor must be soluble enough to beleached out in sufficient amounts to protect the metal but not toleached out in sufficient amounts to protect the metal but not tosoluble so that it will be lost rapidly.soluble so that it will be lost rapidly.

-- The most common coating inhibitors are zinc chromate andThe most common coating inhibitors are zinc chromate andplumbous orthophumbate (red lead) which passivate steel byplumbous orthophumbate (red lead) which passivate steel byproviding chromate and plumbate ions.providing chromate and plumbate ions.

-- These inhibitors are not effective against attack by sea water orThese inhibitors are not effective against attack by sea water orbrines because the high chloride concentration prevents passivationbrines because the high chloride concentration prevents passivationof steel.of steel.






Problems in Application ofProblems in Application of

InhibitorsInhibitors A system must be carefully examined before a program of corrosion A system must be carefully examined before a program of corrosion

inhibition can be lanned effectivel .inhibition can be lanned effectivel .

The examination must include a survey of any adverse effects anThe examination must include a survey of any adverse effects aninhibitor may have on the process in which it is to be used and aninhibitor may have on the process in which it is to be used and ananalysis to detect the presence of interfering substance.analysis to detect the presence of interfering substance.

The most likely adverse effects which organic inhibitors mayThe most likely adverse effects which organic inhibitors mayproduce are due to their polar nature.produce are due to their polar nature.

The requirement that inhibitors must have functional groups thatThe requirement that inhibitors must have functional groups thatare stron l absorbed also im arts to them some de ree of surfaceare stron l absorbed also im arts to them some de ree of surface active properties.active properties.

They may behave as soaps, or detergents and cause foaming,They may behave as soaps, or detergents and cause foaming,formation of emulsion or they may loosen scale formed beforeformation of emulsion or they may loosen scale formed beforeinhibition was started.inhibition was started.



FoamingFoaming

The most appropriate action to take in avoiding difficultyThe most appropriate action to take in avoiding difficultyfrom foamin is to determine where foamfrom foamin is to determine where foam--forminforminconditions exist in the system.conditions exist in the system.

This will consist of places where the inhibitor containingThis will consist of places where the inhibitor containingfluid is agitated with a gas such as in a gas separator, afluid is agitated with a gas such as in a gas separator, acounter current stripper or in a aerator.counter current stripper or in a aerator.

There are three alternative remedies:There are three alternative remedies:

1. An anti1. An anti--foaming agent may be added.foaming agent may be added.

2. tests can be made to select an inhibitor which does2. tests can be made to select an inhibitor which doesnot cause foaming.not cause foaming.

3. the system can be shut down periodically and treated3. the system can be shut down periodically and treatedwith a slug of persistent inhibitor.with a slug of persistent inhibitor.






EmulsionsEmulsions

Emulsions consist of two immiscible liquid phases whileEmulsions consist of two immiscible liquid phases while

Conditions favorable for emulsion formation are theConditions favorable for emulsion formation are thepresence of two liquid phases, agitation and an emulsionpresence of two liquid phases, agitation and an emulsionstabilizer. In this case, the corrosion inhibitor maystabilizer. In this case, the corrosion inhibitor maybehave as an emulsion stabilizer, so the procedure is tobehave as an emulsion stabilizer, so the procedure is toshake the two liquid phases with inhibitor and measureshake the two liquid phases with inhibitor and measurethe time re uired for them to se arate.the time re uired for them to se arate.

if the time required for separation is longer in theif the time required for separation is longer in the

presence of inhibitor than its absence, the inhibitor ispresence of inhibitor than its absence, the inhibitor isemulsion stabilizer.emulsion stabilizer.



PluggingPlugging

A system can be plugged as the result of an A system can be plugged as the result of an’ ’

the fluid.the fluid.

The best preventive measure is to clean theThe best preventive measure is to clean thesystem thoroughly, if possible before inhibitor issystem thoroughly, if possible before inhibitor isapplied.applied.

An alternate or supplementary method in An alternate or supplementary method in

systems w c are very sens t ve to suspen esystems w c are very sens t ve to suspen esolids to protect the sensitive parts withsolids to protect the sensitive parts withtemporary filters.temporary filters.






Creation of New CorrosionCreation of New Corrosion

ProblemsProblems Another possible adverse effect of inhibition is an Another possible adverse effect of inhibition is an

other than the one for which the inhibitor was selectedother than the one for which the inhibitor was selectedto protect.to protect.

For Example:For Example:

Some amines protect steel admirably but will severelySome amines protect steel admirably but will severelyattack copper and brass. Nitrites may attack lead andattack copper and brass. Nitrites may attack lead and

. ,. ,may react in the system to produce a harmful product.may react in the system to produce a harmful product.

In order to avoid these problems you have to know theIn order to avoid these problems you have to know themetallic components of a system and be thoroughlymetallic components of a system and be thoroughlyfamiliar with the properties of the inhibitor to be used.familiar with the properties of the inhibitor to be used. 37

AV Santos & Associates : August 2010 :For Training Purposes Only

Heat Transfer Heat Transfer

Heat transfer is an importantHeat transfer is an important

inhibitors.inhibitors.

Scaling of heat transfer should be avoidedScaling of heat transfer should be avoidedor held to a minimum.or held to a minimum.

Excessive deposits of phosphates, silicatesExcessive deposits of phosphates, silicates

or su a es s ou e avo e ecauseor su a es s ou e avo e ecausethey are difficult to remove by chemicalthey are difficult to remove by chemicalmeans.means.






Economics of InhibitionEconomics of Inhibition

Prevention of corrosion by inhibition may be desirable forPrevention of corrosion by inhibition may be desirable for

1. To extend the life of equipment.1. To extend the life of equipment.

2. To prevent shut downs.2. To prevent shut downs.

3. To prevent accidents resulting from brittle3. To prevent accidents resulting from brittle(catastrophic) failures.(catastrophic) failures.

4. To avoid product contamination.4. To avoid product contamination.

5. To prevent loss of heat transfer.5. To prevent loss of heat transfer.6. To preserve an attractive appearance.6. To preserve an attractive appearance.



The Concept and Development of InspectionThe Concept and Development of Inspectionand Corrosion Monitoringand Corrosion Monitoring

The concept of inspection and corrosion monitoring has developedThe concept of inspection and corrosion monitoring has developedfrom two distinct areas, plant inspection techniques and laboratoryfrom two distinct areas, plant inspection techniques and laboratorycorros on es ng ec n ques, w e or g na a m o assess ng orcorros on es ng ec n ques, w e or g na a m o assess ng orpredicting the corrosion behavior of plant and equipment betweenpredicting the corrosion behavior of plant and equipment betweenshutdowns.shutdowns.

Objectives:Objectives:

-- is to obtain information on the state of operation equipment tois to obtain information on the state of operation equipment topermit the better scheduling of maintenance work, to ease thepermit the better scheduling of maintenance work, to ease theinspection load during shutdowns and to avoid unplanned shutdowninspection load during shutdowns and to avoid unplanned shutdownoccurring because of unforseen deterioration of plant.occurring because of unforseen deterioration of plant.

-- is to obtain information on the interrelation between corrosionis to obtain information on the interrelation between corrosionprocesses and operating variables. To help diagnosis of the problemprocesses and operating variables. To help diagnosis of the problemand to allow improved control of corrosion and more efficientand to allow improved control of corrosion and more efficientoperation of the plant.operation of the plant.






Development of Monitoring MethodDevelopment of Monitoring Method

As a Diagnostic Tool As a Diagnostic Tool

-- -- provide information for the solution of a corrosionprovide information for the solution of a corrosionproblem.problem.

-- Corrosion monitoring is one of the several toolsCorrosion monitoring is one of the several toolsavailable to the investigator, but it is particularly valuableavailable to the investigator, but it is particularly valuable

obtained in other ways, and thus lead to a better orobtained in other ways, and thus lead to a better or

speedier solution.speedier solution.



To monitor the effectiveness of a SolutionTo monitor the effectiveness of a Solution-- A logical extension of the diagnostic application is to A logical extension of the diagnostic application is touse corrosion monitoring techniques to establish whetheruse corrosion monitoring techniques to establish whethera solution has been effective.a solution has been effective.

--investigation, but more permanent installations are beinginvestigation, but more permanent installations are beingused to an increasingused to an increasing oxtentoxtent to provide long termto provide long termassurance.assurance.

To provide Operational or ManagementTo provide Operational or ManagementInformationInformation

--operational variable (e.g. temperature, pH, humidity)operational variable (e.g. temperature, pH, humidity)within limits determined by prior monitoring or otherwithin limits determined by prior monitoring or otherinvestigations. If the significant variable is measured forinvestigations. If the significant variable is measured forother reasons, this measurement can be usedother reasons, this measurement can be used directlyfordirectlyforcorrosion control.corrosion control.






-- If the variable is not measured , or in more complexIf the variable is not measured , or in more complexcases where several variables interact, corrosioncases where several variables interact, corrosionmonitoring information can be used by plant operatorsmonitoring information can be used by plant operators

to control plant operation so as to control corrosion.to control plant operation so as to control corrosion.

s par o a on ro ys ems par o a on ro ys em

-- An extension of the use of monitoring techniques to An extension of the use of monitoring techniques toprovide operating information is to use the monitoringprovide operating information is to use the monitoringinformation directly to control plant, or parts of plant.information directly to control plant, or parts of plant.

-- The use of potential measurements to control anodic orThe use of potential measurements to control anodic orcathodiccathodic protection system is an example, as is theprotection system is an example, as is the

more recent development of using monitoring signals tomore recent development of using monitoring signals tocontrol inhibitor or other additions to cooling watercontrol inhibitor or other additions to cooling watersystems.systems.



-- Clearly, equipment used in this way required a highClearly, equipment used in this way required a high

standard of reliability, and some form of “sell testing”standard of reliability, and some form of “sell testing”feature, and a detailed understanding of the corrosionfeature, and a detailed understanding of the corrosionbehavior of the plant is essential to the successful designbehavior of the plant is essential to the successful designof the control system.of the control system.

As part of a Management System As part of a Management System

-- The data from corrosion monitoring can be useful toThe data from corrosion monitoring can be useful tomanagement in several ways. It can supplement othermanagement in several ways. It can supplement otherinspection techniques, and improve the management ofinspection techniques, and improve the management ofmaintenance and its coordination with productionmaintenance and its coordination with production

schedules.schedules.

-- This approach is used to varying degrees ofThis approach is used to varying degrees ofsophistication in a number of industries. The samesophistication in a number of industries. The sameinformation can also be used with benefits ininformation can also be used with benefits inoptimization and other investigations.optimization and other investigations.






- Developments in computers and data handling havebeen an important stimulus in this areas, since asubstantial mass of the data has to be processed to a

manageable from. Selecting Technique

- monitoring. There are eight techniques in corrosionmonitoring.

1. Time for individual measurement – sometechniques provide information that is effectivelyinstantaneous, while other are necessarily slower in thisres ect.

2. Type of Information obtained – some techniques

provide a measurement of corrosion rate, othermeasure total corrosion, or the remaining thickness,which is not exactly equivalent; yet others provideinformation on the distribution of corrosion on thecorrosion re ime.



3. Speed of response to change – techniques which do not

provide an individual measurement quickly are obviouslyunsuitable for situations where a fast response is required.Not all techniques that provide effectively instantaneousinformation are however capable of a fast response. Where

, ,response can be obtained, but if the measurement is of totalcorrosion, remaining thickness or distribution of corrosion,the speed of response is limited by the ability of thetechnique to discriminate between successive readings.

. –techniques provide information on the behavior of a probeinserted into the plant, which does not necessarily reflectthe behavior of the plant itself. The information obtained isin fact a measure of the corrosivity of the environment,from which plant behavior can be inferred.






5. Applicability to environment5. Applicability to environment – – A fast response is most A fast response is mostreadily obtained from electrochemical measurements whichreadily obtained from electrochemical measurements whichrequire that the environment is an electrolyte; a highrequire that the environment is an electrolyte; a high

electrolytic conductivity is not always necessary however.electrolytic conductivity is not always necessary however.NinelectrochemicalNinelectrochemical measurements can be used in gaseousmeasurements can be used in gaseous

--,, ,,electrolytes.electrolytes.

6. Type of corrosion6. Type of corrosion – – Most corrosion monitoring techniquesMost corrosion monitoring techniquesare best suited to situations where corrosion is general, butare best suited to situations where corrosion is general, butsome provide at least some information on localizedsome provide at least some information on localized

..

7. Difficult of interpretation7. Difficult of interpretation – – Interpretation of the resultsInterpretation of the resultsis often relatively straight forward if the technique is usedis often relatively straight forward if the technique is usedwithin its limitations. The interpretation of the resultswithin its limitations. The interpretation of the resultsobtained by some techniques however, but more difficult.obtained by some techniques however, but more difficult.47


8. Technological Culture – some techniques are inherently

technically sophisticated; this tends to limit their use toorganizations with a strong technological culture. Mostothers are much less demanding in this respect.

In principle, the available techniques could be ranked in anorder or merit for each of these eight criteria. In practice,the relative merits change with circumstances so that aformal treatment of this type is potentially misleading. Themost useful general approach is therefore, to consider the

s reng s an wea nesses o e ec n ques n v ua y anprovides a reasonable starting point.






CORROSION IN CHEMICALCORROSION IN CHEMICAL

CLEANINGCLEANING Chemical CleaningChemical Cleaning

-- It is a specialized cleaning technique which is findingIt is a specialized cleaning technique which is findingextensive use today as a substitute or supplement forextensive use today as a substitute or supplement forconventional mechanical cleaning methods. A properlyconventional mechanical cleaning methods. A properlyimplemented chemical cleaning program will provideimplemented chemical cleaning program will provideeffective cleaning which is both rapid and economical.effective cleaning which is both rapid and economical.

-- The primary incentive for utilizing chemical cleaning is toThe primary incentive for utilizing chemical cleaning is toreduce unit downtime, and in most cases it is morereduce unit downtime, and in most cases it is morerapid, more efficient and less costly than mechanicalrapid, more efficient and less costly than mechanicalcleaning.cleaning.

-- It can often be accomplished in place without having aIt can often be accomplished in place without having adismantle the equipment and the need for cranes,dismantle the equipment and the need for cranes,hoists, and similar mechanical equipment can behoists, and similar mechanical equipment can bereducedreduced 49


CHEMICAL CLEANINGCHEMICAL CLEANING






-- Proper application of chemical cleaning can also haveProper application of chemical cleaning can also havefavorable effect on refinery fuel costs, manpower allocationsfavorable effect on refinery fuel costs, manpower allocationsand preventive maintenance.and preventive maintenance.

-- Chemical cleaning can be applied to almost any type ofChemical cleaning can be applied to almost any type ofprocess equipment. Exchangers, towers, drums, pipelines,process equipment. Exchangers, towers, drums, pipelines,

, , , , ,, , , , ,equipments have all been successfully cleaned by chemicalequipments have all been successfully cleaned by chemicalmethods.methods.

-- The most commonly used chemical cleaning method includeThe most commonly used chemical cleaning method includesolvent cleaning, high pressure jet cleaning and pipeline pigsolvent cleaning, high pressure jet cleaning and pipeline pigc ean ng. e spec c ec n que o e use epen s on ec ean ng. e spec c ec n que o e use epen s on eequipment to be cleaned and the characteristics of theequipment to be cleaned and the characteristics of the

deposit to be removed.deposit to be removed.



A STEP BY STEP PROCEDURE IN CHEMICAL CLEANING A STEP BY STEP PROCEDURE IN CHEMICAL CLEANING

1.1. Obtain and analyze a representative sample of the foulingObtain and analyze a representative sample of the foulingdeposit.deposit.

2.2. Determine the solvent and/or other chemicals to be usedDetermine the solvent and/or other chemicals to be usedfor cleaning. Perform a materials study to determine thefor cleaning. Perform a materials study to determine thecapability of the chemicals with the vessel material.capability of the chemicals with the vessel material.

3.3. Determine the technique to be used on the specific piece ofDetermine the technique to be used on the specific piece ofequipment.equipment.

4.4. Plan cleaning operations and prepare tools and equipment.Plan cleaning operations and prepare tools and equipment.

5.5. Perform cleanin .Perform cleanin .

6.6. FollowFollow--up, including final inspections, recording data andup, including final inspections, recording data andreview of equipment performance subsequent to return toreview of equipment performance subsequent to return toservice.service.






-- Chemical cleaning can be used safely and effectivelyChemical cleaning can be used safely and effectivelyproviding:providing:

1.1. Materials of construction are reviewed prior to the treatmentMaterials of construction are reviewed prior to the treatmentto determine compatibility with the solvent.to determine compatibility with the solvent.

2.2. A suitable inhibitor is used. A suitable inhibitor is used.

3.3. The treatment is intelligently controlled to avoid excessiveThe treatment is intelligently controlled to avoid excessivetemperature and velocity as well as to check corrosive ions.temperature and velocity as well as to check corrosive ions.

- The possible hazards of cleaning equipment with chemicalscan be classified into two categories:

1. The hazards of handlin the solvents and chemicals.

2. Hazards of toxic gases and vapors formed during the

chemical cleaning treatment.However, if the proper precautions are taken in planning and

performing the chemical cleaning operation, these hazardscan be eliminated.



CORROSIONCORROSION

-- Before a chemical cleaning job is performed, it is importantBefore a chemical cleaning job is performed, it is importantto know the materials of construction of the equipment to beto know the materials of construction of the equipment to becleaned since the choice of solvents and inhibitors arecleaned since the choice of solvents and inhibitors are affected by metallurgical considerations.affected by metallurgical considerations.

-- Severe corrosion can occur when the incorrect solvent isSevere corrosion can occur when the incorrect solvent isused. In some cases, acids, even when inhibited can causeused. In some cases, acids, even when inhibited can causeserious corrosion.serious corrosion.

-- Refineries use many different types of alloys. Frequently aRefineries use many different types of alloys. Frequently a

different materials so that the solvent may provide andifferent materials so that the solvent may provide anelectrolytic solution which establishes active corrosion cells.electrolytic solution which establishes active corrosion cells.

-- Other considerations in preventing corrosion are properOther considerations in preventing corrosion are properenvironmental control of solvent: temperature, velocity andenvironmental control of solvent: temperature, velocity andventing of gases.venting of gases.






CORROSIONCORROSION



-- Excessive temperatures or velocities can cause corrosionExcessive temperatures or velocities can cause corrosion

problems.problems.-- Corrosion of process equipment during a chemical cleaningCorrosion of process equipment during a chemical cleaning

treatment will not occur to any appreciable extent providingtreatment will not occur to any appreciable extent providingthe job has been properly planned and the operationthe job has been properly planned and the operation

..

The most important factors that must be considered toThe most important factors that must be considered toprevent corrosion are:prevent corrosion are:

1.1. The materials must be compatible with solvents.The materials must be compatible with solvents.

2.2. Suitable inhibitors must be used.Suitable inhibitors must be used.

3.3. Treatment must be controlled properly.Treatment must be controlled properly.






A. Materials

- The materials of construction of the equipment to be cleaned

must be reviewed carefully to determine whether the materialsare compatible with the solvents to be used.

- Carbon steels offers good resistance to inhibited hydrochloricacid even at temperatures up to 200F however changes incomposition in carbon steel change the corrosioncharacteristics.

- Free machining, high sulfur steels are susceptible to acida ac .

- Stainless Steel are more resistant to corrosion than carbonsteels.

- Chromium-nickel alloys are especially resistant. Inhibitedhydrochloric acid should not be used on high chromium steelscontaining little or no nickel. 57


CARBON STEELCARBON STEEL






3

STAINLESS STEELSTAINLESS STEEL



Chromium-nickel alloys






3

The Type 300 series stainless steels behave on one ofThe Type 300 series stainless steels behave on one ofthree different manners when in contact withthree different manners when in contact withsolutions:solutions:

1. Passive1. Passive – – stainless steels in the passive condition require astainless steels in the passive condition require acon nuous supp y o a r or oxygen o ma n a n e pass vecon nuous supp y o a r or oxygen o ma n a n e pass vefilm on the metal surface.film on the metal surface.

2. Active2. Active – – if the passive film is removed, the surface is in anif the passive film is removed, the surface is in anactive state and the stainless steel is no more corrosionactive state and the stainless steel is no more corrosionresistant than carbon steel.resistant than carbon steel.

3. Borderline3. Borderline-- this condition exists when some areas are passivethis condition exists when some areas are passiveand others active. Pitting occurs at the activated areas. Theand others active. Pitting occurs at the activated areas. Thepits result in stressed areas and cracks develop causing thepits result in stressed areas and cracks develop causing themetal to fail.metal to fail.



- Pro-Copper and its alloys may be cleaned with non-oxidizing

acids.

- Copper, phosphor-bronze, admiralty metal, yellow brass, andcupro-nickel can be cleaned with inhibited hydrochloric acid.

- Aluminum and its alloys may be cleaned with mild alkalis andoxidizing acids.

- Inhibited hydrochloric acid or strong alkali such as causticcannot be used. Chromic acid as well as mixtures of soda-ash trisodium hos hate and sodium metasilicate can be used in many cases without danger of corrosion.

- Lead is satisfactory with weak sulfuric acid, however,hydrocholic acid as well as caustic are corrosive to lead.






3

B. InhibitorsB. Inhibitors

--

Inhibitors are added to acid solvents to retard corrosion ofInhibitors are added to acid solvents to retard corrosion ofequipment during chemical cleaning.equipment during chemical cleaning.

-- There are many types of inhibitors available for differentThere are many types of inhibitors available for differentuses. Certain inhibitors are best suited for particular metals.uses. Certain inhibitors are best suited for particular metals.

-- Presence of brass, bronze cast iron, carbon steel andPresence of brass, bronze cast iron, carbon steel andstainless steel as well as the scale characteristics in manystainless steel as well as the scale characteristics in manycases influence choice of inhibitors.cases influence choice of inhibitors.

The most im ortant and effective inhibitors available areThe most im ortant and effective inhibitors available are classified into four different types:classified into four different types:

(1). Inorganic (2). Organic metal (3). Organic(1). Inorganic (2). Organic metal (3). Organic--aliphatic (4).aliphatic (4).OrganicOrganic--aromatic.aromatic.



-- The effectiveness of an inhibitor depends on the film formedThe effectiveness of an inhibitor depends on the film formed

between the acid and the steel surfaces. This film is formedbetween the acid and the steel surfaces. This film is formedduring the acid attack on the steel or other metallic surface.during the acid attack on the steel or other metallic surface.

-- When acid attacks steel, iron is dissolved at the anodic areasWhen acid attacks steel, iron is dissolved at the anodic areasas ferrous ions and hydrogen is formed at the cathodes.as ferrous ions and hydrogen is formed at the cathodes.

C. Treatment ControlC. Treatment Control

-- All inhibitors have certain temperature limitations. These All inhibitors have certain temperature limitations. These

temperature points:temperature points:

1.1. The temperature at which the inhibitor becomes ineffective.The temperature at which the inhibitor becomes ineffective.

2.2. The temperature at which the complete decomposition ofThe temperature at which the complete decomposition ofthe inhibitor occurs.the inhibitor occurs.






3

TREATMENT CONTROLTREATMENT CONTROL



-- maximum safe treating temperature for most inhibitors is inmaximum safe treating temperature for most inhibitors is in

the range of 180F to 200F. The temperature at which thethe range of 180F to 200F. The temperature at which theinhibitor decomposes is somewhat higher.inhibitor decomposes is somewhat higher.

-- If the effective inhibition temperature is exceeded, the effectIf the effective inhibition temperature is exceeded, the effecto e n or can e res ore y ower ng e empera ure.o e n or can e res ore y ower ng e empera ure.

-- Prolonged periods at temperatures exceeding the effectiveProlonged periods at temperatures exceeding the effectivelimit can result in corrosion even though the inhibitor is notlimit can result in corrosion even though the inhibitor is notpermanently destroyed.permanently destroyed.

-- Excessive solvent velocities while circulating inhibited acidExcessive solvent velocities while circulating inhibited acidcan also cause equipment damage. Inhibitors are notcan also cause equipment damage. Inhibitors are noteffective on surfaces when flow velocities are high or wheneffective on surfaces when flow velocities are high or whenthe flow is very turbulent. However, limited circulation isthe flow is very turbulent. However, limited circulation isfrequently necessary after the equipment is filled with solventfrequently necessary after the equipment is filled with solvent






3

SafetySafety

-- Personnel must exercise all precautions in chemicalPersonnel must exercise all precautions in chemical

cleaning operations in order to eliminate thecleaning operations in order to eliminate thedangers associated with handling the variousdangers associated with handling the various

during actual cleaning activities.during actual cleaning activities.

-- Some of the materials used in chemical cleaning canSome of the materials used in chemical cleaning cancause severe burns or skin irritations.cause severe burns or skin irritations.

-- The most dangerous are sulfuric acid, chromic acid,The most dangerous are sulfuric acid, chromic acid,caustic andcaustic and phenolicphenolic compound.compound.



-- d Sulfuric acid and caustic soda can cause severe burns ofd Sulfuric acid and caustic soda can cause severe burns of

the eyes and skin.the eyes and skin.

-- Chromic acid can causes severe skin irritation and phenolChromic acid can causes severe skin irritation and phenolcan cause severe burns or death through skin absorption.can cause severe burns or death through skin absorption.

-- Other materials may also cause mild burns or skinOther materials may also cause mild burns or skinirritations and must be handled carefully. And someirritations and must be handled carefully. And somechlorinated solvents are toxic.chlorinated solvents are toxic.

--

provided with safety clothing. Protective rubber gloves andprovided with safety clothing. Protective rubber gloves andgoggles are mandatory; rubber suits and hat may also begoggles are mandatory; rubber suits and hat may also benecessary.necessary.






3

-- The most serious hazards in chemical cleaning are created byThe most serious hazards in chemical cleaning are created bytoxic gases and vapors which are generated during thetoxic gases and vapors which are generated during thecleaning process.cleaning process.

-- Particularly hazardous are the volatile hydrides of sulfur,Particularly hazardous are the volatile hydrides of sulfur,arsen c an p osp orous. ny o ese, w en con ac e yarsen c an p osp orous. ny o ese, w en con ac e ysolvents, can generate toxic gases. These gases are formedsolvents, can generate toxic gases. These gases are formedby two methods:by two methods:

1. By the action of dilute acid on sulfides,1. By the action of dilute acid on sulfides, phosphidesphosphides andandarsenidesarsenides..

2. By the solution of nascent hydrogen on compounds of these2. By the solution of nascent hydrogen on compounds of thesemetals. Nascent hydrogen may be formed by attack of acidmetals. Nascent hydrogen may be formed by attack of acidon steel and copper.on steel and copper.



-- Hydrogen sulfideHydrogen sulfide can be vented to the atmospherecan be vented to the atmosphere

providing a convenient high point is available and only smallproviding a convenient high point is available and only smallquantities are generated.quantities are generated.

-- Sulfide depositsSulfide deposits, which from hydrogen sulfide when, which from hydrogen sulfide whenrea e w y roc or c ac are common n a re nery.rea e w y roc or c ac are common n a re nery.

Cyanides are formed in fluid catalytic cracking and theseCyanides are formed in fluid catalytic cracking and thesedeposits can be found in the vapor recovery units. Thesedeposits can be found in the vapor recovery units. Theseare primarilyare primarily ferroferro--ferriferri cyanides characterized by bluishcyanides characterized by bluishdeposits.deposits.

-- Arsenic Arsenic may come from admiralty brass, crude or frommay come from admiralty brass, crude or fromcooling or process water. Some inhibitors contain arsenic.cooling or process water. Some inhibitors contain arsenic.These inhibitors should not be used to inhibit acid forThese inhibitors should not be used to inhibit acid forchemical cleaning.chemical cleaning.






3

-- Phosphorus is found in steel and could producePhosphorus is found in steel and could produce phosphinephosphine ininthe presence of nascent hydrogen.the presence of nascent hydrogen.

-- These gases may be detected by specially designed detectorsThese gases may be detected by specially designed detectorsor by laboratory methods. The presence of hydrogen sulfideor by laboratory methods. The presence of hydrogen sulfidecan be determined qualitatively with a MSA ( Mine Safetycan be determined qualitatively with a MSA ( Mine Safety

Appliance) Hydrogen Sulfide detector or qualitatively with a Appliance) Hydrogen Sulfide detector or qualitatively with astrip of filter paper moistened with lead acetate.strip of filter paper moistened with lead acetate.

-- MSA Hydrogen Cyanide Detector is satisfactory to detect thisMSA Hydrogen Cyanide Detector is satisfactory to detect thisgas. However, any hydrogen sulfide andgas. However, any hydrogen sulfide and mercaptansmercaptans presentpresentmust be scrubbed out with lead acetate and acetic acid.must be scrubbed out with lead acetate and acetic acid.

-- HydrogenHydrogen released during acid cleaning operations canreleased during acid cleaning operations cancause a serious explosion when mixed with air and ignited.cause a serious explosion when mixed with air and ignited.



-- Inhibitors retard this reaction, however, hydrogen evolutionInhibitors retard this reaction, however, hydrogen evolutioncannot be stopped completely and must be vented properly.cannot be stopped completely and must be vented properly.

-- Carbon Dioxide is evolved from deposits containingCarbon Dioxide is evolved from deposits containingcarbonates when reacted with hydrochloric acid. It is notcarbonates when reacted with hydrochloric acid. It is not

can cause suffocation. The gas is heavier than air and tendscan cause suffocation. The gas is heavier than air and tendsto settle in low places.to settle in low places.

-- Sulfur dioxide is formed from deposits containing sulfates. ItSulfur dioxide is formed from deposits containing sulfates. Ithas an extremely disagreeable odor and is severely irritatinghas an extremely disagreeable odor and is severely irritating

. .

-- The hazards created by gases evolved during the cleaningThe hazards created by gases evolved during the cleaningprocess can be eliminated if proper precautions are used.process can be eliminated if proper precautions are used.NonNon--toxic gases can usually be safely vented to thetoxic gases can usually be safely vented to theatmosphere.atmosphere. 72





3

-- If chemical cleaning is being done in a confined place orIf chemical cleaning is being done in a confined place orenclosed building vent hoses should be extended out ofenclosed building vent hoses should be extended out ofdoors.doors.

-- Occasionally, solvent return hoses can be used as vents,Occasionally, solvent return hoses can be used as vents,ox c gases may e ven e o a are w ere ey can eox c gases may e ven e o a are w ere ey can e

burned safely.burned safely.

-- Disposal of such gases by venting up a chimney is not alwaysDisposal of such gases by venting up a chimney is not alwayseffective, however, with un favorable atmospheric conditions,effective, however, with un favorable atmospheric conditions,the gas could settle back to the ground and create a seriousthe gas could settle back to the ground and create a serioushazard.hazard.

-- No smoking or welding should be permitted during any stageNo smoking or welding should be permitted during any stageof the cleaning operation.of the cleaning operation.



The following table lists various gases occasionally encountered,The following table lists various gases occasionally encountered,

their source and reasons why they are dangerous.their source and reasons why they are dangerous.

GasGas SourceSource EffectEffect

H dro en Sulfide de osits PoisonousH dro en Sulfide de osits Poisonous

Sulfide mainly iron sulfideSulfide mainly iron sulfide

Arsine Arsenic compounds Poisonous Arsine Arsenic compounds Poisonous

also from metals & oilsalso from metals & oils

PhosphinePhosphine Phosphorous compounds PoisonousPhosphorous compounds Poisonous

& Phosphorous in steel& Phosphorous in steel

Hydrogen Cyanide compounds found PoisonousHydrogen Cyanide compounds found Poisonous

Cyanide in cat. crackingCyanide in cat. cracking 74 AV Santos & Associates : August 2010 :





3

Gas Source EffectGas Source Effect

Sulfur Dioxide Sulfite compounds dangerous to eyesSulfur Dioxide Sulfite compounds dangerous to eyessuffocating odorsuffocating odor

irritatin toirritatin to res ires i--

ratoryratory organs.organs.

Carbon Dioxide Carbonate deposits nonCarbon Dioxide Carbonate deposits non--toxic.toxic.

causes suffocationcauses suffocation

Hydrogen Acid attack on steel ExplosiveHydrogen Acid attack on steel Explosive

Nitrous oxide HCL reaction with AsphyxiatingNitrous oxide HCL reaction with Asphyxiating

nitrate compoundsnitrate compounds

used forused for passivatingpassivating 75 AV Santos & Associates : August 2010 :


HAZARDOUS SYMBOLSHAZARDOUS SYMBOLS






3

OTHER CHEMICAL CLEANING METHODSOTHER CHEMICAL CLEANING METHODS

--

Several other specialized chemical cleaning techniques haveSeveral other specialized chemical cleaning techniques havebeen successfully applied to a limited extent to clean variousbeen successfully applied to a limited extent to clean variousequipment. These may entail greater expense and have lessequipment. These may entail greater expense and have lessversa y so a e occas on o use s rare. ese me o sversa y so a e occas on o use s rare. ese me o sinclude the following:include the following:

a.a. Ultrasonic vibrationUltrasonic vibration

b.b. Pressure fracturin of tube de ositsPressure fracturin of tube de osits

c.c. Explosive methodsExplosive methods

d.d. Chlorinated solvent vapor phase methodChlorinated solvent vapor phase methode.e. High circulation rateHigh circulation rate



ULTRASONIC VIBRATIONULTRASONIC VIBRATION






4

EXPLOSIVE METHODEXPLOSIVE METHOD



HIGH CIRCULATION RATEHIGH CIRCULATION RATE






4

-- Controlled oxidation is a technique being developed toControlled oxidation is a technique being developed toremoveremove carbonaciouscarbonacious deposits from towers. The principledeposits from towers. The principleinvolves the controlled flameless combustion of the cokeinvolves the controlled flameless combustion of the coke--likelike

deposits. Temperatures are controlled at approximately 900Fdeposits. Temperatures are controlled at approximately 900Fwith inert gas.with inert gas.

-- The vapor phase cleaning method is for tank cleaningThe vapor phase cleaning method is for tank cleaningapplication and utilizes an airapplication and utilizes an air--steam mixture to atomizesteam mixture to atomizesolvents selected to remove heavy layers of oil impregnatedsolvents selected to remove heavy layers of oil impregnatedrust deposits from the tank shells.rust deposits from the tank shells.

COORDINATION AND CONTROL OF CHEMICALCOORDINATION AND CONTROL OF CHEMICALCLEANINGCLEANING

-- Considerable technical control and coordination are requiredConsiderable technical control and coordination are requiredin order to make a chemical cleaning program most effective.in order to make a chemical cleaning program most effective.



-- A prime objective is to minimize equipment turnaround times A prime objective is to minimize equipment turnaround times

and thorough preplanning and scheduling are extremelyand thorough preplanning and scheduling are extremelyimportant if this is to be achieved. Capable and adequateimportant if this is to be achieved. Capable and adequatesupervision must be provided.supervision must be provided.

-- ur ng ma or urnaroun s, mproper sc e u ng an con rour ng ma or urnaroun s, mproper sc e u ng an con rocan result in having in having large groups of men waiting forcan result in having in having large groups of men waiting forequipment or materials or for other units to be completedequipment or materials or for other units to be completedbefore they can proceed with their particular jobs.before they can proceed with their particular jobs.

-- The interdependence of various operating units makes itThe interdependence of various operating units makes it

essential that schedules be adhered to as closely as possible.essential that schedules be adhered to as closely as possible.






4

GOOD DESIGN APPROACH CAN PREVENT CORROSIONGOOD DESIGN APPROACH CAN PREVENT CORROSIONPROBLEMSPROBLEMS

1. Structural Steel Shape1. Structural Steel Shape -- always present a problem. However,always present a problem. However,because they are a basic building materials, they must bebecause they are a basic building materials, they must be

“lived with”. The outside of an angle is difficult to coat “lived with”. The outside of an angle is difficult to coatbecause coatings tend to pull away from a point or shapebecause coatings tend to pull away from a point or shapeedge.edge.

2. Sharp edge or square2. Sharp edge or square--cut steel should be eliminatedcut steel should be eliminatedwherever possible. Coating materials tend to run away fromwherever possible. Coating materials tend to run away froman edge. If the coating is applied by brush and the painteran edge. If the coating is applied by brush and the painter

brushes away from the edge, the coating is invariablybrushes away from the edge, the coating is invariablybrushed off.brushed off.



STRUCTURAL STEEL SHAPESTRUCTURAL STEEL SHAPE






4

SHARP EDGE 0R SQUARESHARP EDGE 0R SQUARE

CUT STEELCUT STEEL



3. Riveted structure or tank can cause difficulty; the coating3. Riveted structure or tank can cause difficulty; the coating

discontinuities are formed around rivets. There are 3discontinuities are formed around rivets. There are 3ordinary rivet shapesordinary rivet shapes – – round, pointed and countersunk.round, pointed and countersunk.

4. Welded Joints4. Welded Joints – – in process equipment, steel tanks, andin process equipment, steel tanks, andstructures are preferable to bolted or riveted joints, from astructures are preferable to bolted or riveted joints, from acorrosion design standpoint.corrosion design standpoint.

5. Rough Welding5. Rough Welding – – is another difficulty: rough welds should beis another difficulty: rough welds should beground smooth. All welds should be double coated for sureground smooth. All welds should be double coated for sureprotection. Weld flux is a strongly alkaline hydroscopicprotection. Weld flux is a strongly alkaline hydroscopic

material.material.

6. Skip6. Skip--WeldingWelding-- is widely used in the construction ofis widely used in the construction ofequipment. This is the technique of welding a 2 in. bead,equipment. This is the technique of welding a 2 in. bead,then skipping 2,4,8 and 10 in. before laying another 2 in.then skipping 2,4,8 and 10 in. before laying another 2 in.bead.bead.






4

RIVETED STRUCTURERIVETED STRUCTURE



WELDED JOINTWELDED JOINT






4

ROUGH WELDINGROUGH WELDING



SKIP WELDINGSKIP WELDING






4

7. Lap7. Lap--weldingwelding-- is yet another method of tank construction.is yet another method of tank construction.Here welding is continuous on the outside only, leaving theHere welding is continuous on the outside only, leaving theplates lapped on the inside. As can readily be seen, thisplates lapped on the inside. As can readily be seen, thisprovides a crevice extremely difficult to coat properly, intoprovides a crevice extremely difficult to coat properly, intowhich moisture, corrosive gases and corrosive liquids canwhich moisture, corrosive gases and corrosive liquids can

..

8. Steel angles8. Steel angles – – placed back to back, are often used to formplaced back to back, are often used to formtrusses for a building structure, these angles are ordinarilytrusses for a building structure, these angles are ordinarilyseparated approximately ¼ in. gap is difficult to protectseparated approximately ¼ in. gap is difficult to protectproperly wherever corrosive conditions exist. Corrosiveproperly wherever corrosive conditions exist. Corrosiveumes pene ra e rea y.umes pene ra e rea y.

9. Cone roofs or9. Cone roofs or unbrellaunbrella--type roofstype roofs-- on storage tanks usuallyon storage tanks usuallyconsists of a center pole with Iconsists of a center pole with I--beam rafters extending out tobeam rafters extending out tothe edge of the tank and the steel plate roof laid directly onthe edge of the tank and the steel plate roof laid directly ontop of these Itop of these I--beams.beams. 91


LAP WELDINGLAP WELDING






4

STEEL ANGLESSTEEL ANGLES



CONE ROOFCONE ROOF






4

PipePipe – – should be an ideal type of surface to protect againstshould be an ideal type of surface to protect againstcorrosion. It is cylindrical and, in general, does not have anycorrosion. It is cylindrical and, in general, does not have anysharp or supports for any structure exposed to severesharp or supports for any structure exposed to severe

corrosion.corrosion.

oa ng nsu a onoa ng nsu a on – – s ano er prac ce w c requ res a en ons ano er prac ce w c requ res a en onand which often causes considerable difficulty. In areas ofand which often causes considerable difficulty. In areas ofsevere corrosion in a plant, the insulation itself maysevere corrosion in a plant, the insulation itself maydeteriorate if there is any way for fumes to reach it.deteriorate if there is any way for fumes to reach it.



NONNON--DESTRUCTIVE TESTING/INSPECTIONDESTRUCTIVE TESTING/INSPECTION

INTRODUCTIONINTRODUCTION

--examination of materials or manufactured articles, in orderexamination of materials or manufactured articles, in orderto determine their fitness for certain purposes, withoutto determine their fitness for certain purposes, withoutimpairment of their desirable properties.impairment of their desirable properties.

LIQUID PENETRANT INSPECTIONLIQUID PENETRANT INSPECTION

-- ququ pene ranpene ran processes are nonprocesses are non-- es ruc ve es nges ruc ve es ngmethods for detecting discontinuities that are open to themethods for detecting discontinuities that are open to thesurface. They can be effectively used in the inspection ofsurface. They can be effectively used in the inspection ofnonporous, metallic materials, both ferrous and ferrous.nonporous, metallic materials, both ferrous and ferrous.PenetrantPenetrant inspection is basically a simple process.inspection is basically a simple process.






4

LIQUID PENETRANTLIQUID PENETRANT

INSPECTIONINSPECTION



MAGNETIC PARTICLE INSPECTIONMAGNETIC PARTICLE INSPECTION

-- Magnetic particle inspection is a nonMagnetic particle inspection is a non--destructive method ofdestructive method ofdetecting the presence of cracks, laps, burst, tears, splits,detecting the presence of cracks, laps, burst, tears, splits,seams inclusions, segregations, laminations, shrinks, coldseams inclusions, segregations, laminations, shrinks, coldshuts, porosity, lack of fusion and similar discontinuities inshuts, porosity, lack of fusion and similar discontinuities in

-- , ., .will detect discontinuities that are open to the surface, butwill detect discontinuities that are open to the surface, buttoo fine to be seen with the naked eye.too fine to be seen with the naked eye.

EDDY EDDY--CURRENT INSPECTIONCURRENT INSPECTION

-- It is consists of observing the interaction betweenIt is consists of observing the interaction between

electromagnetic fields and metals. Eddyelectromagnetic fields and metals. Eddy--current methods ofcurrent methods ofinspection are effective with bothinspection are effective with both ferroferro--magnetic andmagnetic andnonferrononferro--magnetic metals.magnetic metals.






MAGNETIC PARTICLEMAGNETIC PARTICLE

INSPECTIONINSPECTION



EDDYEDDY--CURRENT INSPECTIONCURRENT INSPECTION






Application of Eddy Application of Eddy--current and Electromagnetic methods ofcurrent and Electromagnetic methods ofinspection to castings can be divided into the categories:inspection to castings can be divided into the categories:

1.1. Detecting nearDetecting near – – surface flaws such as cracks, voids,surface flaws such as cracks, voids,inclusions, blowholes and pinholes (eddyinclusions, blowholes and pinholes (eddy – – currentcurrentnspec onsnspec ons

2.2. Sorting according to alloy, temper, electrical conductivity,Sorting according to alloy, temper, electrical conductivity,hardness and other metallurgical factors (primarilyhardness and other metallurgical factors (primarilyelectromagnetic inspection)electromagnetic inspection)



THE ENDTHE END






REMINDERREMINDER

Always refer to the appropriate codes and standards Always refer to the appropriate codes and standards



If you need further assistance, you may contactIf you need further assistance, you may contact

Victor Lachica and Tony SantosVictor Lachica and Tony Santos

Mobile: +63Mobile: +63--917917--867867--58785878

-- -- --Email:Email: [email protected]@gmail.com

[email protected]@gmail.com






Thank you very much!!!Thank you very much!!!



We would like to acknowledgeWe would like to acknowledge

all persons, and/or organizationsall persons, and/or organizations

for the information used in this training materialfor the information used in this training material

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Fundamentals of Inhibitors

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