a new approach corrosion monitoring chemengjune07

7/28/2019 A New Approach Corrosion Monitoring ChemEngJune07

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Most assets depreciate, losing

value over time as a resultof wear and tear, age, or ob-solescence. Corrosion, like

depreciation, results in the often hid-

den cost of a non-cash expense mea-surable in terms of reduced operatinglife that reduces the value of as-sets. Many engineers in the chemicalprocess industries (CPI) see corrosionon a straight-line basis in terms ofrepair, maintenance and replacementduring fixed-interval turnaround in-spections. New technology, however,can assess corrosion deterioration inrealtime, using the plant control-and-automation system.

The latest technology links corro-

sion to process conditions more di-rectly and immediately. It also allowscorrosion depreciation to be assessedin much-shorter time intervals withthe ability to control and mitigate therate of damage, and more accuratelyfactor-in its true economic impact onplant operations.

Illustrating the importance of cor-rosion depreciation is the fact thatcorrosive attack leads to plant break-downs with some very considerablecosts. Consider these figures based on

recent studies: The annual cost of corrosion in the

U.S. is estimated to be about $300billion (about 4% of the gross domes-tic product)

For the petrochemical and pharma-ceutical sectors, the annual cost isabout $2.5 billion

The annual corrosion cost in the CPIis over 10% of the annual plant capi-tal expenditures across these indus-trial sectors

Globally, the cost of corrosion in theCPI appears to be about $50 billionper year and is projected to climbstill higher over the next five years

Indeed, corrosion gives a whole newmeaning to the term depreciation,particularly when both immediate-and longer-term effects of corrosion

are considered.Still, to many CPI engineers, corro-

sion is simply a routine part of plantoperations and a cost of doing busi-ness. A corrosion specialist is calledwhen a problem arises. Once the prob-lem is solved, the plant operates moreor less as before, until the next upsetoccurs. The major impact of corrosionto the business lies in costs associatedwith lost production, health, safetyand environmental issues, and legalliabilities.

New technology allows corrosionmonitoring via the plant distributedcontrol system (DCS), whereby corro-

sion measurement is coupled to a suiteof key, realtime process variables. Thisprocess can lead to gains in many partsof the corporate balance sheet.

Process optimization often bringsan immediate reduction in direct costsand also helps increase plant produc-tivity and revenues while minimizingcorrosion damage. Ultimately, it canprovide major gains through reducedcorrosion depreciation allowance andincreased plant asset life.

Staying ahead of the damageIn many regards, the corrosion engi-neers job is viewed as that of a histori-cal record keeper. This is because tradi-tionally, the tasks to measure corrosiondamage have been documented overrelatively long time intervals typi-

Feature Report

34 ChemiCal engineering www.Che.Com June 2007

Cover Story

A New Approach toCorrosion MonitoringRussell D. Kane

Honeywell Process SolutionsThe impact of corrosion on assets and processes

is great. Advances in technology allow engineers

to assess corrosion in a whole new way,

with realtime monitoring and the ability

to link deterioration with process conditions

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Figure 1. These data, which depict realtime corrosion data on a hydrocarbon/water stream, show that the rate of corrosion is not steady over time. Peak corrosionepisodes occur


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cally months to years using corro-sion coupons and periodic inspections.This historical information is thenused to confirm or predict the effective-ness of corrosion control measures, therisk of future failures, and the need formaintenance. This approach, however,

has a major limitation.Modern plant operations are likely

to encounter changes in feed, processconditions and control limits that arebased on current market conditions. Inone recent case, a plant feed changedevery two-to-three days based on de-liveries of particular constituents,which were being purchased on aglobal basis and influenced by marketprices. Unfortunately, these constitu-ents also had widely varying impuritylevels that led to corrosivity changes,which made historical corrosion mea-surement worthless.

Now, however, emergence of online,

realtime corrosion monitoring can im-prove the relevance of corrosion mea-surements. This approach reduces themanual effort and the high expensesrequired to obtain this information.Most importantly, corrosion informa-tion can be obtained quickly some-

times in a matter of minutes andin a manner consistent with that usedfor collecting other key process data.

This new approach utilizes exist-ing data acquisition and automationsystems found in production facilities.For example, the plant DCS is used tomonitor and control processes, trendkey process information, and manageand optimize system productivity. Cor-rosion monitoring can be integratedinto this system, and the data canbe automated and viewed with otherprocess variables (PVs). Advantagesof this approach over stand-alone sys-tems include the following:

more cost effectiveness less manual labor to accomplish

key tasks a greater degree of integration with

in-place systems to record, controland optimize

efficient distribution of importantinformation (corrosion and processdata, related work instructions andfollow-up reports) among differentgroups required for increased workefficiency and ease of documentation

The rate of corrosion

The perception of constant-ratecorrosion. In field and plant opera-tions, corrosion is typically viewed

as the difference between two mea-surements performed over a ratherlong interval of time. These corrosionmeasurements commonly come frommeasured changes in metal thickness(such as from ultrasonic inspectionreadings made on components andelectrical-resistance measurementstaken by probe elements) or mass-loss readings (such as weight-lossof coupons). The measurements aretaken on the order of weeks, monthsor sometimes years.

There are two major shortcomingsto this approach: data indicate cor-rosion only after the damage has ac-cumulated, and they provide only anaverage rate-of-metal loss during themeasurement interval. Peak corro-sion rates are not documented and,most importantly, the specific time pe-riods of peak corrosion rates and thecorresponding process conditions arenot identified.

This scenario has led to the gener-ally held misconception that corrosion

in chemical processes occurs at a rela-tively constant rate over time. In real-ity, a majority of corrosion experiencesin these processes actually occurs dur-ing short periods when specific processconditions develop.Actual monitoring shows peakcorrosion rates. An example of thiseffect is shown in Figures 1 and 2.The data was obtained from a studyconducted by the U.S. Dept. of Energyto identify best practice corrosion-measurement techniques for corro-sion monitoring [1,2]. In this case,the environments were primarily oil(with varying water fraction, as may

ChemiCal engineering www.Che.Com June 2007 35

Figure 2. Realtime corrosion data in a dehydrated hydrocarbon-gas streamshows six episodes of corrosion over two months (upper graph). The bottom plothighlights a shorter interval to reveal the detail of a single upset that is likely relatedto upsets in dehydration

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occur during normal production con-ditions) and dehydrated hydrocar-bon gas.

The system was monitored with re-

altime corrosion measurements usingelectrochemical techniques and probesthat were specifically selected for theircompatibility with these low-waterenvironments. The data were obtainedwith a totally remote and automatedcorrosion-measurement system thatinvolves multiple electrochemical tech-niques, solar power and wireless datatelemetry back to a control center.

The data in Figure 1 shows that thecorrosion rate was mostly minimalover an approximately two-month pe-

riod. However, there were about 20 ep-isodes of high corrosion rate (corrosionupsets that were one to two orders ofmagnitude above baseline levels) dur-ing this period. Generally, the trend incorrosion rates increased with watercontent, but it is clear that water con-tent was not the only factor another

variable was likely in play. In oil/watersystems, periodically stratified flowconditions can develop at low flow-rates where the water separates fromthe oil. This can lead to an increase in

corrosion activity, particularly at thesix oclock position in piping. In thiscase, the realtime corrosion measure-ment was more reflective of corrosionupsets than the infrequent processmonitoring being performed.

A similar situation was found for areportedly dehydrated gas streamthat was susceptible to periodic dew-point conditions due to plant upsets.Figure 2 shows electrochemical moni-toring data from a dehydrated hy-drocarbon gas stream. During a two-

month period, six episodes of highercorrosion rate were observed. Whereasthe magnitude of the corrosion excur-sions was not as great as in the oil/brine system, the excursions do consti-tute periodic and significant increasesin corrosivity, particularly since cor-rosion allowances are typically muchsmaller in these dry systems.

These cases highlight situationsthat could be remedied by better pro-cess control (separation, dehydrationand/or flow control), or more effec-tive dosing of inhibitors at intervalsdefined by the realtime corrosionmeasurement, rather than based on

historical, average corrosion rates. Arelated condition in many gas streamsis the need to maintain inlet gas qual-ity to reduce out-of-specification con-

ditions from moisture, CO2 or H2S.

Understanding the techniquesOffline measurement. Corrosioncoupons have been the backbone ofindustrial corrosion monitoring formore than 50 years. Coupons must bepre-weighed, distributed to remote lo-cations, installed, retrieved, examined,cleaned and re-weighed before data areprocessed. Therefore, a good deal of cor-rosion engineering and related techni-cal-staff time is consumed with manual

and often routine tasks, as well as withmanipulating and viewing historicallyaveraged, offline data. Coupon mea-surements are offline, labor intensiveand not easily configured for automa-tion and control systems.

Approaching corrosion assess-ment from an automation and con-trol point of view frees up staff time.Rather than spending time manuallyretrieving corrosion data, personnelcan, for example, use their time toexamine, interpret and understand

critical underlying system attributesand relationships.Online measurement. In some cases,corrosion probes used to monitor indus-trial plants and pipelines are connectedto field dataloggers that take corro-sion-rate measurements over a periodof weeks or months. This approach isoften referred to by corrosion engineersas online monitoring despite the factthe data cannot be accessed, viewed oracted upon in an online, realtime man-ner. These techniques can retrospec-

tively identify peak corrosion rates andtime periods.

Corrosion probe data using conven-tional methods are, however, typicallyconsidered qualitative, at best, due tolimitations in the 1960s measurementtechniques used in most field instru-ments. This information is viewed inisolation, without the PVs that allowits interpretation (PVs that relateto periods of corrosion upsets). It istherefore up to the corrosion engineerto locate and piece together relevantprocess information and manuallybuild correlations to understand thecauses of corrosion upsets.

With these remote online measure-ments, technical staff often travel tothe remote locations in order to re-trieve corrosion data files. Then, they

manually analyze the logged data.Under these conditions, the corrosionengineer is viewed as a bearer of badnews, because the information is usu-ally available only after the damagehas occurred or, even worse, after criti-cal failures have taken place.

The current perception is that thereis a high per-point cost associatedwith conventional corrosion monitor-ing approaches, largely due to the highcost of a separate infrastructure andlarge commitment of time and labor.

Additionally, there is a low perceivedvalue because the data is historicaland is viewed weeks and months pastdue. Given this perception, there is atendency to limit resources for corro-sion monitoring because the approachis expensive with only a limited chanceof success. In many cases, problemsare viewed after the fact, and there isno way to directly link cause and effectin a time frame that allows the dam-age to be cost effectively preventedor minimized. Accordingly, corrosion

measurement is relegated to mainlya confirmational reading of second-ary importance rather than a primary

variable that can be controlled and op-timized with the process.

This perception is somewhat sur-prising. Many plant operators aretrying to squeeze out a 12% improve-ment in efficiency and productivity.Corrosion costs are, however, one ofthe few areas where double-digit cost-reduction improvements could be ob-tained, particularly if lost production

opportunity is included.Estimates indicate that between 25

and 40% of the approximately $300billion lost to corrosion in the U.S. eachyear could be saved with better controlefforts. In several petrochemical cases(such as fractionator overhead andhydroprocessing), the cost of a singlecorrosion failure can be in the range of$35 million to $60 million [3]. Even afew days of lost production can involveover $500,000 in losses.Online, realtime measurement.Feedback from realtime corrosion-rate data and adjusted chemical dos-age can offer additional gains in ef-

Cover Story



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ficiency and reduced operating costs,as well as extended run time. Fur-ther confirmation of the potentialcost savings reaped through betterand faster corrosion information andimplementation of improved processcontrols are apparent in the recentU.S. Cost of Corrosion Study [4] andreferenced in recent NACE technicalcommittee reports [5].

Corrosion monitoring has developedfrom a manual, offline process to an on-line, realtime measurement (Figure 3).The initial driving force for this migra-tion is the benefit of automation; thatis, reduced time and effort to obtaincorrosion data with high data reliabil-ity. Corrosion monitoring takes on newmeaning when it can be viewed at ahigher frequency (within minutes) thatis consistent with the way process vari-ables are measured. More data bringincreased statistical relevance, quicker

response time, and a greater ability tounderstand corrosion in the context ofthe process being monitored.

The second driver for this migrationis the ability to integrate the corrosiondata immediately with process data.This is done in an automated man-ner, within the plant DCS, rather thanby the manual methods traditionallyavailable to the corrosion engineer.Some of the usual PVs that are usedand measured in CPI control systemsinclude the following: temperature;pressure; flowrate; chemical injectionrate; moisture content; valve actua-tion (opening/closing); level measure-

ment; and analytical data, such aspH, dissolved oxygen and others.

One historical barrier to integrat-ing corrosion measurements withinthe plant DCS is that online corrosionmeasurements have been qualitativerather than quantitative due to limi-tations of single technique transmit-ters with limited on-board processingcapacity. For use as a process vari-

able, corrosion measurements need tobe quantitative, since the system willutilize the data to make automatedassessments, generate alarms, anddetermine the economic consequencesof process changes and/or upsets.With this requirement also comes theconcomitant need to accurately assesscorrosion modality (such as generalcorrosion, pitting, local area attack).

It is generally accepted that thereis no perfect method for assessing allcorrosion mechanisms. In most cases,

however, corrosion involves electrontransfer in an electrically conductivelocal or bulk environment. It has beenshown that electrochemical methodscan be used to monitor corrosion fordew point conditions, many multi-phase (oil/water) conditions with aslittle as 12% water, and even somefireside high-temperature corrosionsituations in fossil-fueled boilers andwaste incineration [611]. Therefore, ifproperly used, accurate corrosion mea-surements can be made in a matter ofminutes in most chemical processes.

One recently released multivari-able corrosion transmitter employs a

Figure 3. Corrosion monitoring has evolved from offline to online, and online,realtime measurements

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suite of automated elec-trochemical techniquesthat run in the on-boardmemory of a single trans-

mitter and are used tocomplement one another.This transmitter gener-ates general corrosion-rate data by combiningLinear Polarization Re-sistance (LPR) and Har-monic Distortion Analy-sis (HDA) for greatercorrosion-rate accuracy.The transmitter alsoprovides completely newinformation obtained on

the localized nature ofcorrosion from Electro-chemical Noise (ECN)measurements. When

joined in an automatedcycle, these techniquescan provide two critical, operator-levelcorrosion PVs at a similar frequencyof measurement as expected for cur-rent process variables. These opera-tor-level corrosion PVs are: Corrosion rate: LPR corrosion rate

adjusted for a measured B value

(see below) determined by HDAPitting factor: Derived from ECN

and LPR measurements, providing athree-decade logarithmic scale rang-ing from general corrosion, througha cautionary zone, to localized pit-ting corrosion

Two additional PVs can also be pro-vided through the process control sys-tem for specialist observation, diag-nostics and intervention:B value: Also called the Stern Geary

constant, the B value is derived from

HDA involving the realtime mea-surement of the anodic and cathodicTafel slopes. This value is used toadjust the LPR corrosion rates withthe electrochemical processes inthe system

Corrosion Mechanism Indica-tor (CMI): Indicating conditionsand trends of passivity in stain-less alloys, corrosion inhibition orscale formation

In addition to these types of realtimemeasurements, there may be a need toinclude other online-compatible mea-surements into the process-controland automation system, when they

can bring additional value or longer-term corroboration for uses in assetassessment and integrity evaluation.

These corrosion assessment tech-niques are even more attractive ifthey can be easily automated and cou-pled with the modern communication

methods such as wireless technologies.Techniques include electrical-resis-tance-corrosion measurements, ultra-sonic thickness, pulsed-eddy currentand fiber-optic strain measurement,as well as other ancillary techniquesthat may become available as thesecomplementary technologies develop.

ImplementationIn a modern chemical operation, theentire facility is controlled by automa-tion and control systems. The arrange-

ments of process equipment, vesselsand piping are far too complex foroperators to personally control everyaspect of their operations. Therefore,they rely on a system of data acquisi-tion and associated computer routinesand applications to analyze the dataand apply rule-based methodologiesfor assessing variations in processconditions and prioritizing responses.In modern industrial environments,these systems also provide manage-ment of safety and security. This infra-structure has vastly improved chemi-cal plant productivity.

In the 1970s, when process automa-

tion-and-control technologies were firstemployed, chemical plants operated atabout 70% of daily productivity levels.With newer technologies, productivityhas progressed to over 90%. With cur-rent technology and initiatives such asabnormal situation management, the

goals are to increase the number ofoperating days per year and increaseproductivity levels to over 95%.

A 2004 survey indicates that corro-sion is by far the major factor account-ing for chemical plant failures (Figure4). Comparing the 2004 survey resultswith data from a similar 1984 sur-

vey shows the situation appears un-changed over the past 20 years. There-fore, it is a foregone conclusion that amore proactive (realtime) approach tocorrosion mitigation is needed. This

approach must integrate into automa-tion and control strategies if the above-mentioned productivity goals are to beachieved while keeping a critical eyeon plant reliability and safety [12].

Examples of integrating corrosioninto the process-control environment,where data is displayed in the sys-tem historian together with other keyperformance indicators (KPIs), areshown in Figures 5 and 6. In Figure 5,the screen shows the major parame-ters that are normally used to monitorthe health of a cooling-water system.The electrochemical corrosion mea-surement captures a corrosion event

Cover Story


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Figure 4. A2004 survey of causes for failure in refining and petrochemical plants in Japanshows that a majority of the failures were due to corrosion (left chart). The right side shows failuresby type of material of construction


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where the LPR/HDA corrosion ratesjump when the blowdown occurs. Itis also demonstrated that a large in-

jection of corrosion inhibitor (as anautomated process) decreases thecorrosion rates until they returned tonormal levels. Figure 6 shows a simi-lar configuration for a lean, aminesystem reboiler circuit.

Corrosion monitoring in actionAn important aspect of integrationwith the automation and control sys-tem is the seamless connectivity be-tween varying job functions. An ex-

ample of this integration in a chemicalplant is illustrated by Rohm and Haas,Deer Park plant near Houston, Tex. In2006, Rohm and Haas became one ofthe early adopters of online corrosionmonitoring technology.

At the Deer Park site, the companyplanned an alloy upgrade of more than$500,000 after failing to determinewhy two similar chemical units wereshowing widely different signs of cor-rosion damage. While one of the plantshad low corrosion rates, the other cor-roded at very high rates, causing rapidfailure of stainless-steel piping.

After traditional monitoring meth-ods proved ineffective, the companyinstalled corrosion transmitters. Bycommunicating via the HART proto-

col, the transmitters fed corrosion datadirectly in the process control system,allowing it to be alarmed, histor-ized, trended and assigned to processgroups. With this information, the cor-rosion data was then seamlessly cor-related with other process variables,providing a broader and realtime viewof plant operating conditions.

The results benefited both operatorsand the corrosion experts. Plant oper-ators could access current, actionableprocess-variable information, includ-

ing a time-trended general (uniform)corrosion rate. Additionally, the solu-tion indicated the mode of corrosion(localized or pitting) detection calleda pitting factor. Corrosion staff couldaccess the same information with theadded capability to review data for di-agnostic purposes.

Using this new system, Rohm andHaas identified two process scenariosthat contributed to the difference incorrosion rates. First, one units cor-rosion rate was higher immediately

after a shutdown. The company thendiscovered and replaced a leaky valvethat was allowing water into the sys-tem. Secondly, process corrosion wasmore severe when a particular recir-culation condition occurred. Engineersmodified the process, and the plantavoided this condition on the second,more corrosive unit.

The solution saved Rohm and Haasmore than $500,000 in capital expen-diture, and the company devised anoperating strategy that avoids corro-

sion. Additionally, operators utilizedrealtime corrosion data in combina-tion with process information to im-prove equipment reliability, stability,integrity and uptime.

Whereas corrosion is a knownquantity to corrosion engineers, iteludes most operators and processengineers. The above-mentionedexample shows how coupling corro-sion data with process data creates atighter working relationship betweencorrosion, process engineers andplant operators. Including corrosionas an online process variable makesplant personnel aware of the process

ChemiCal engineering www.Che.Com June 2007 39

Figure 5.This display shows corrosion with other KPIs for a heat exchanger inthe plant data historian

Figure 6. In this example, corrosion monitoring is displayed together with otherprocess variables for a lean, amine reboiler line


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conditions that can initiate corrosion.Examples of such conditions includeunintentional aeration by venting ofequipment to atmosphere, additionsof oxidizing agents and aggressivecatalysts, lack of dew-point control in

normally dehydrated systems, and ex-cessively high velocities in attemptsto increase unit productivity.

Online corrosion detection in a pro-cess-control environment will giveplant operators immediate feedbackon the state of corrosion relative towhat they are doing so that they canactively participate in managing ex-cessively high corrosion costs.

New values and insightsIntegration of corrosion with modern,

industrial process-control technolo-gies offers substantial operational andcost-saving opportunities for plantoperators. Consider the following ex-amples of value propositions obtainedfrom discussions with refinery opera-tions and corrosion personnel: Increased ability to process crudes

with higher margins big savingsand increased profits

Reduced cost of unscheduled shut-downs as an example, a 400,000-bbl/d unit could shut down for three daysto repair a corrosion leak. The costat a $5 margin on feed is $6,000,000.With better integration of corrosion

monitoring and plant economics, thecost of unscheduled shutdowns (dueto accelerated corrosion depreciation)can be properly evaluated and consid-ered by plant management. Typically,a plant will have to run at a higher

throughput to make up the unplannedshort fall

Improved asset reliability resultingin improved run length 10% re-duction in maintenance costs

Improved unit operation as a re-sult of better corrosion monitoringthat may result in a 2% increasein throughput, or potentially theability to process more of a lower-quality feed

Reduced health, safety and envi-ronmental exposure resulting from

fewer unscheduled emissions to theenvironment 3% savings

Improved safety record as a resultof fewer shutdowns 5% reductionin cost

Savings due to optimized chemicalcost resulting from better monitor-ing 10% reduction

Increased operator effectiveness bybringing the corrosion data onlineand in the control room. This leadsto improved decision making withnew insights and improved issueresolution time

The benefits from the final bullet itemcan be seen in a recent implementa-

tion of online, realtime corrosion mon-itoring in a hydrocarbon oxidationprocessing plant [11]. This exampleinvolves monitoring performed at aplant where much of the equipmentwas constructed of carbon steel and

304L and 316L stainless steels.Decades of debottlenecking and

other process modifications led to cor-rosion problems. After a year of unsuc-cessful efforts to untangle material-related problems offline, an online,realtime, electrochemical corrosion-monitoring system was installed. Ma-terials engineers, process engineers,and plant operators saw immediatechanges in corrosion behavior causedby specific variations in the process,enabling them to work together to

identify process modifications and re-medial actions to substantially reducedamage to equipment.

Based on the results of the initialprocess evaluation that required onlya few weeks, five predominant fac-tors were confidently identified thatrelated to the chemical aggression ofthe plant environment, which variedsubstantially with process and opera-tional variables. These included: An upstream vessel was on an auto-

matic pump-down schedule so thatit pumped its contents into a reac-tor approximately once per hour.Every time the vessel pumped down,

Feature Report


New froNtiers: wireless

One potential barrier to rapid acceptance of corrosion as anonline PV stems from past practices. Since corrosion mea-

surement has traditionally been offline, corrosion-monitor-ing points that accepted corrosion coupons or probes to be readby data loggers have not been connected to the DCS. There is,therefore, no existing wiring to these points in the plant. In manycases, the cost of the wiring is many times higher than the trans-mitter cost.Wireless technology, however, is making its way into the plantautomation-and-control environment. One approach to this tech-nology is to establish a wireless mesh of monitoring points aroundthe chemical plant. This wireless net is particularly valuable forbringing many new types of information into the plant control-and-automation system. Initially, this new information will bemainly used for diagnostics, documenting work flow, staff safety,and many other non-control functions. This is also likely to be thecase for corrosion in its new realtime form.In this regard, wireless technology is the enabler for setting up a

much wider-ranging network of realtime corrosion data points inthe process plant than would be possible using conventional wiredtransmitters. Locations can be dictated by critical need rather thanthe convenience of wire placement. This expanded network alsobrings more complete coverage and redundancy. Since corrosion

can be a localized phenomenon, the ability to monitor more lo-cations provides greater assurance that key locations have been

included. Data from different probes can also be used to corrobo-rate each other, making the approach to corrosion control morerobust than possible with conventional approaches.After integrating corrosion data with other PVs, existing pro-

grams (such as the advanced process-control applications avail-able around the plant DCS) can provide further assessment toidentify key relationships between corrosion and other variables.Examples of functions handled in these applications are linearand non-linear modeling capabilities and data-validation tools.These programs provide a means to positively identify single andmulti-variant relationships between corrosion and other PVs.

Early event detection is another functionality of the automationand control system, whereby correlations can be made betweencorrosion and other variables so that the sequence of processevents leading to corrosion upsets can be identified. Finally, animportant milestone for corrosion as a critical PV is its use inclosed-loop, process-control functions. These functions can includemulti-variant process control to optimize production while control-ling corrosion within specific operational boundaries, and dosingcorrosion inhibitors and other anti-corrosion chemicals, so that theapplication is based on need rather than historical trends.


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the corrosiveness of the stream

increased Operators had varied the concentra-

tion of a neutralizing chemical in the

process. However, contrary to expec-tations, it was found that increasingfeedrate of a neutralizer increased

corrosion rates rather than reducingthem. This new information helped

to both reduce corrosion rates andprovide chemical engineers with

new insight into the chemistry ofthe process

Following an initial evaluation ofthe corrosion data, a plant techni-

cian pointed out that an increase incorrosion rate of the 304L occurred

right after; they mixed a new batchof catalyst and it varied with fee-

drate, which was controlled to mini-mize corrosive attack

The corrosion rate also varied quitesignificantly with process and oper-

ational events. These included not-ing that the corrosion rate of carbon

steel correlated with the quantityof a key gaseous chemicals used in

the process Short-term spikes to very high cor-

rosion rates were observed week

after week. The corrosion-ratespikes coincided with the pumpingof a laboratory waste stream into

the process. Operators changed theirprocedure to dispose of lab samples

another way, thus stopping the cor-rosion spikes

Conclusion

Corrosion behavior in process envi-ronments has a number of influenc-

ing factors that can vary with timeand cause dynamic corrosion events.

The long intervals associated withinspections and offline measure-

ments do not afford the operator theopportunity to correlate corrosion ex-

cursions with operating and processparameters, making control a diffi-

cult proposition. By implementing anappropriate and correspondingly dy-

namic means of corrosion appraisal,chemical manufacturers can better

manage industrial processes andrelated corrosion prevention treat-

ments, minimize corrosion upsetsand failures, and maximize the avail-

ability of the plant assets.

EditedbyDorothyLozowski

References

1. Bullard, S. J., others. Laboratory Evalua-tion of an Electrochemical Noise System forDetection of Localized and General Corro-sion of Natural Gas Transmission Pipelines,Corrosion/2003, Paper No. 03371 (San Diego,

Calif., March 1720, 2003), NACE Interna-tional, Houston, Tex.

2. Covino, Jr., B. S., others. Evaluation ofthe Use of Electrochemical Noise Corro-sion Sensors for Natural Gas TransmissionPipelines, Paper No. 04157, Corrosion/2004(New Orleans, La., March 28-April 1, 2004),NACE International, Houston Tex., 2004.

3. Kane, R. D., others. Major Improvement inReactor Effluent Air Cooler Efficiency, Hy-drocarbon Processing, Sept. 2006, pp. 99111.

4. Corrosion Costs and Preventive Strategiesin the United States, Supplement to Materi-als Performance, NACE International, Hous-ton, Tex., July 2002, p. 3.

5. Alawalia, H., Corrosion Technology Gaps

Analysis, Report Prepared for the NACETechnical and Research Committee (TRAC)and Technical Coordinating Committee(TCC), Presentation at CTW/06, NACE In-ternational, Houston, Tex., 2006.

6. Kane, R. D., others. Online, Real-Time Cor-rosion Monitoring for Improving PipelineIntegrity Technology and Experience,Corrosion/2003, Paper No. 03175, NACE In-ternational, March 2003.

7. Kane, R. D. and Trillo, E., Evaluation ofMultiphase Environments for General andLocalized Corrosion, Corrosion/2004, PaperNo. 04656, NACE International, March2003.

8. Eden D. A. and Srinivasan, S., Real-time,On-line and On-board: The Use of Computers,Enabling Corrosion Monitoring to Optimize

Process Control, Corrosion/2004, Paper No.04059, NACE International, March 2004.

9. Kane, R. D. and Campbell, S., Real-TimeCorrosion Monitoring of Steel Influenced byMicrobial Activity (SRB) in Simulated Seawa-ter Injection Environments, Corrosion/2004,Paper No. 04579, NACE International, March2004.

10. Covino, Jr., B. S., others. Fireside CorrosionProbes for Fossil Fuel Combustion, Corro-sion/2006, Paper No. 06472, NACE Interna-tional, March 2006.

11. Eden, D. C. and Kintz, J. D., Real-time Cor-rosion Monitoring for Improved ProcessControl: A Real and Timely Alternative toUpgrading of Materials of Construction,Paper No. 04238, Corrosion/2004, NACE In-ternational, Houston Tex., 2004.

12. Yamamoto, K., Technical Proposals toPrevent Material Failures And Accidentsin Chemical Process Industries, Corro-sion/2006, Paper No. 06211, NACE Interna

Author

Dr. Russell Kane, an inter-nationally recognized expertin corrosion evaluation andmodeling, is the director ofcorrosion services at Honey-well Process Solutions (14503Bammel N. Houston Road,Suite 300 Houston, Tex.;Email: [email protected]; Phone: 281-444-2282

X32). Kane received NACEsA.B. Campbell and Techni-

cal Achievement Awards and ASTMs Sam TourAward for distinguished contributions to corro-sion research, development, and evaluation. Hisdoctorate is in metallurgy and materials sciencefrom Case Western Reserve University.

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