Indi an Journal of Experimental Biology Vol. 4 1. September 2003, pp. 101 2- 1022

Microbiologically influenced corrosion in petroleum product pipelines - A review

N Mulhukumar, A Rajasekar, S Ponmari appan, S Moh,ll1an , S Maruth::uTIuthu *, S Muralidharan, P Subramanian , N Palaniswamy & M Raghavan

Elec troche mi ca l Protcction and Biofoulillg Group, Corrosion Science and Eng ineering Division. Central Elec trochemical Rcsearch Institute. Karaikudi , 630 006, Indi a.

Microbiologically influenced corrosion is responsible fo r most of thc internal corrosion problems in oi l transportati on pipelincs and storage tanks. One problematic area in treat ing gas lines is the occurrence of the strati fica tio n of water in the line. Under these conditions, corros io n inhibitors do [lot come into contact properly and oil and inhibitors undergo degradation. The ro le o f bacteria on o il degradation, the consequences of oil degradation in fuel systems and its influ ence on corrosion have been explained in detail. Besides, factors influencing o n degradatio n of o il and corrosion inhibitors have also been discussed. Mechanism of microbiologicall y influenced corrosion in o il pipeline has been explained . Many of the mi sappl icati on of biocidesli nhibito rs occ ur mainl y because the charac teri stip of biocides/inhibitors are not conside red before usc in pipc line indu stry. Li st of biocides and monitoring programme have been collected from lite rat ure and presented.

Keywords: Biocides, Corrosion, Degradation o f o il , Mi crobial corrosion, Oil pipelines, Pe troleum prod uct, Storage tan ks

Corrosion refers to the deterioration of the material s (metallic and non-metallic) due to their reaction with the environment. Rusting of iron with the formation of iron oxide is a typical example of cOITosion. Corrosion of metals and alloys leads to enormous losses to the country. Large amount of coating materials like paints, as well as corrosion res istant alloys are needed for controlling corrosion. By understanding the mechani sm of corrosion and the principle involved in the methods of protection of the same, the country would be able to save at least 15-20% of the total loss, amounting to about Rs. J 5,000 crores annu all i .

Microbiologically intluenced corrosion (MIC) Microbial corrosion is recogni zed as one of the

major problems in various fields. The biological growth causes foulin g and corrosion problems. A large variety of bio-organi sms can enhance the corrosion rate of metals through their metabolic processes. The ways in which these organisms influence corrosion have been described in the literature2

.3 . Particularly it has been shown that the presence of bio-organisms in any environment results in locali zed rather than general corrosion . However,

*Correspondent author: E-mail : maruth a_ m @yahoo.com Phone: 04565- 227550-59 Fax : 9 1-4565 -227779

the ability of these bio-organi sms in deposits, relatively in large amounts with meta l ions, sugges ts that they participate in corrosion processes4

•

Microbiolog ically influenced corrosion (MIC), is responsible for most internal corrosion found in o il transmission pipelines. The type of corrosion caused by microbes results in sharp-sided rounded pits and often with pits within the pits. These are typically scattered randomly along the pipe whenever the line has become water-wet, either when low ve locitie result in water lying i.n low spots in the line, or when the water is more than about 30% of the liquid phase. The pitting occurs in the bottom of the line, and often occurs as linear strings of pits associated either with the oil-water contact phase or along the edge of sediment deposits. Water can stratify and collect in pipelines when the velocity is too s low, typically below 3-4 fUsec, or if the pipeline is operated in a 'srop-start' mode.

When bacteria grow on the walls of the pipe, they develop into coloni es containing many types of bacteria, which help each other in li fe. Well-known types, which cause corrosion , include acid-producing bacteria (APB), sulphate-reducing bacteria (SRB), iron bacteria (IB) and manganese oxidizing bacteria (MoB), SRB and ac id producing bacteria are the two types of bacteria commonly found in oil and gas pipe lines. SRB produce hydrogen sulphide, while APB generate acetic acid/sulphuric ac id, both of

.....

MUTHUKUMAR 1.:1 al.: MICROBIOLOGICALLY INFLUENCED CORROSION 1013

which are highly corrosive to the pi, le. Many other types of bacteria like manganese ox idizing bacteria and heterotrophic bacteria are pre~CIll. Iron bacteria precipitate the iron present in sol uti on arising from corrosion and form a tubercle on the top of the corrosion pit.

The present review deals with t\\ O parts : (1) role of oil degradation on microbio ll)gically induced corrosion and (2) oil degradation d llt to microbes .

Microbial corrosion is one amclI lg the many forms of corrosion that contributes to substantial losses to the economy. This is an interdi~.ciplinary subject, which requires at least a basic u ll derstanding in the field of microbiology, chemistr). biochemistry and metallurgy. By definition, it refe, " to the degradation of metallic structures resulting due to the activity of a variety of microorganisms, wili l;h either produce aggressive metabolites to rem'..: r the environment corrosive or able to particip ~\ l e directly in the electrochemical reaction occu iT ing on the metal surface.

Microorganisms present in aqueous environment form biofilm on solid surfaces. Biofilm consists of populations of microorganisms and their hydrated polymeric secretions. Numerous types of organisms may exist in any particular biufilm, ranging from strictly aerobic bacteria at the water interface to anaerobic bacteria such as sulphate reducing bacteria (SRB) at the oxygen depleted metal surface. The presence of biofilm can contribute to corrosion in three ways:

1. Physical deposition, 2. Production of corrosive by-products, and 3. Depolarization of the corrosion cell caused by chemical reaction .

Many of the by-products of microbial metabolism including organic acids and hydrogen sulphide are corrosive. These materials can concentrate in the biofilm causing accelerated metal attack. Corrosion tends to be self-limited due to the build-up of corrosion reaction products. However, microbes can absorb some of these materials in their metabolism, thereby removing them from the anodic and cathodic sites. The removal of reaction products, termed depolarization, stimulates further corrosion. The surface exhibits its scattered areas of localized corrosion, unrelated to the flow pattern . a .

Microorganisms associated with corrosion

Fung; Two forms of fungi that are commonly associated

with corroding metal are filamentous forms (mould)

and unicellular forms (yeasts). The filamentous forms are branched and a tangled mass referred to as mycelium. This releases organic acids as metabolites, which enhances corrosion. Fungi are the most desiccant resistant microorganisms and can remain active down to aw = 0.60. Most of the 'fungi are aerobes and are only found in aerobic habitats. Furgi are non-photosynthetic organi sms, having a vegetative structure known as hypae. The outgrowth is a single microscopic reproductive cell or spore. A mass or thread like hypae make up a mycelium, mycelia are capable of almost wide finite growth in presence of adequate moisture and nutrients so that fungi often reach macroscopic dimensions. Spores, the non-vegetative dormant stage, can survive long periods of unfavourable growth conditions e.g. drought and starvation . When conditions are favourable, spores germinate. Fungi ubiquitous in atmospheric and aquatic environment where they assimilate organic material and produce organic acids including oxalic, formic , acetic and citric acid. Fungal contamination and decomposition of hydrocarbons are well documented . Cladosporium resinae, the kerosene fungus, grew in 80mg water per litre of kerosene.

Little and Ra/ demonstrated metal ion binding by fungal mycelia, resulting in metal ion concentration cells on the metal surface. Differential aeration caused by the adhesive or fungal mats can cause crevice corrosion. Besides the decrease in bulk pH also accelerates corrosion due to metabolites produced during the growth by fungi.

Bacteria These organisms can either be autotrophic or

heterotrophic and either aerobic or anaerobic. Heterotrophic bacteria derive their energy and carbon requirements from organic sources. Autotrophs are bacteria, which obtain their energy from the light or by the oxidation of inorganic materials and the carbon by assimilation . Anaerobic bacteria do not require oxygen for their growth . It is the major group in moist soil and water contributing to corrosion process. Sulphate reducing bacteria (SRB), sulfur-oxidizing bacteria are the major group involved in microbial corrosion .

Sulphate reducing bacteria (anaerobic corrosion) The role of hydrogenase activity in SRB related

corrosion of mild steel is unclear. Hydrogenase positive SRB can oxidize the molecular hydrogen generated at the cathodic sites to facilitate 'cathodic

1014 INDIAN J EXP BIOL, SEPTEMBER 2003

depo lari zation6. In this mechani sm, the combination of adsorbed H-atoms produces H2S gas and thi s is considered to be the rate-controlling step. Bacteria effectively increase the hydrogen evolution rate and thereby the activity increases the corrosion rate. Besides, stimul ation of anodic reaction by bacteriall y produced sulphide has also been suggested. Moreover, the initi a l corrosion rate that was accele rated by iron sulphide in a biofilm system, has been attributed to both "anodic and cathodic depolarization7. However, corros ion engineers consider the role of corrosion process in oxygen free environment that is princ ipa lly dependent on their ability to produce ferrous suphide as suggested by King et al8

• Besides these sul phides have been claimed as semiconductors.

Acid producing bacteria The most corrosive metabolites produced directly

by microorganisms seem to be ac id producers9. Acetic

and butyric ac ids are exa mpl es of such corrosive microbial products. The sulfur ox idi zing bacte ri a e.g. Thiobacillus sp. produce sulfuric ac id from sulfur or sulfide. They occur commo nl y in solids, so ils and water that contai n sulfide minerals . In some buried pipelines, production of sulfuri c ac id has been reported 10. Corrosio n of concrete and steel pipes carrying muni c ipa l water has a lso been related to locali zed production of sulfuric acid by Thiobacillus Sp9.

Iron reducing bacteria Various Pseudomonas sp. have been implicated in

the reducti on of ferric (Fe3+) to ferrous ion (Fe2+) 1 I. As ferric ion is insoluble except at very low pH, ferric salts protect the metal surface from further corrosion due to chemical acti vity. Ferrous salts are mostly soluble and therefore reduction of ferric salts resul ts in the removal of the protective layer. Thus, iron reducing Pseudomonas sp. promotes corrosion directl y.

Iron oxidizing bacteria The aerobic iron ox idi z ing bacteria namely

Pseudomicrobiwn sp. and Gallionella sp. ox idize ferrous (Fe2+) to ferric io n. Tubercles are initia ll y formed by the deposition of iron and manganese ox ide9

. The tubercles have a steep pH gradient, the pH inside being very 10wQ.

Manganese oxidizing bacteria It has been fo und that the active ly metabolizing

manganese ox id izing bacte ria deposi t Mn02 creating anaerobic arena that would favour the grm" ti, of sulfur reducers whose ac ti vity at low va lues of

electrochemical potent ia l might further stimul ate the corros ion process initiated by the Mn02 ennoblement. Xu et al. 12 proposed that the loss of pass ivity or inte rference with repass ivatio n mig ht arise from the production of strong e nvironmenta l ox idants such as Mn (lII ) complexes, which may initi ate loca li zed corros io n of passive metals .

SRB stimulates a pre-existing acti ve corros ion in mild steel and the biogenic sulfide reacts w ith ferrous io ns a lready solubili zed from the metal substratum. The biominerali sed Mn02 arises from the ox idati on of so luble manganese in the bulk medium and makes corros ion poss ibl e th at would not o therw ise occur. SRB sews to initi ate a series of reactions that are the refore autocatalyti c. In the case of Mn02. it is reduced as the cathod ic reductant and must, therefore, be continuously repleni shed by ongoi ng mi crob ial activity. The two microbi a ll y influenced cathod ic reaction s occur at different e lec trochemica l potentials but the essential redox characte ri stics remain as suc h. Thi s considerably strengthens the e lec trochemical! physiological e lectro n transfer hypothes is l 3

.15 in a

microbially influenced corrosion by ex tending its va lidity to acti ve, mild and pass ivated stai nless steels.

Role of microbes on oil degradation ZoBell 16 reviewed the ac ti o n of microorgani sms on

hydrocarbons. He recogni zed that many microorganisms have the ability to ut ili ze hydrocarbons as sole source of energy and these microorgani sms are w idely di stributed in nature. He further recogni zed that microbial utili zat ion of hydrocarbons was hi ghl y dependent on the che mical nature of the compounds within the petroleum mi xtures and on the enviro nmental determinants.

Twenty-one years after ZoBel I ' s 16 c lass ic rev iew, the super tanker Torrey Canyon sank in the Eng li sh Channel. With thi s inc ident , attentions of the sc ientific community were dramatically focused on problems of oil pollution . After this event, several studies were initi ated on the fate of problems of o il pollution . Several studies were a lso initi ated o n the fate of petroleum in varied ecosystem. Biodegradation of petroleum in natura l ecosystem is compi ex . The evol ution of the hydrocarbon mi xture depends on the nature of the o il , the nature of the microbial community, a nd a vari ety of environmental facto rs, which influence mi crobia l activ ities 17.19.

Hydrocarbon utilizing microorganisms The ab ility to degrade petroleum hydrocarbons is

not restricted to a few microbia l genera. A di verse

MUTHUKUMAR el (I/.: MICROBIOLOGICALLY INFLUENCED CORROSION 1015

group of bacteria and fungi have been shown to have this ability. Zobell 16 in his review noted that more than 100 species representing 30 microbial genera had been shown to be capable of utilizing hydrocarbons. In a review, Bartha and Atlas20 too listed 22 genera of bacteria. 1 algal genus and 14 genera of fungi, which had been demonstrated to contain members, those utilize petroleum hydrocarbons. All of these micro­organisms had been isolated from aquatic environments. The most important (based on frequency of isolation) genera of hydrocarbon utilizers in aquatic environments were Pseudomonas sp., Achromobacter sp., Micrococcus sp., Nocardia sp., Candida sp., Vibrio sp., Acinetobacter sp., Brevibacterium sp. , Rhodotorula sp., Sporobolomyces sp., Corynebacterium sp. , and Flavobacterium Sp20. Walker et al. 21

compared the abilities of bacteria and fungi in the degradation of hydrocarbons. The following genera were included in their study Candida sp., Sporobolomyces sp., Hansenula sp., Rhodotorula sp., Cladosporium sp. , Penicillium sp. , Aspergillius sp., Pseudomonas sp., Vibrio sp., Nocardia sp. and Rhobium sp. Walker et al. 22 isolated Vibrio sp, Pseudomonas sp. and Acinatobacter sp. from oil­contaminated sediments and Pseudomonas sp. and Coryneform sp. from oil free sediment. A large number of Pseudomonas sp. have been isolated that are capable of utilizing petroleum hydrocarbons. The genetics and enzymology of hydrocarbon degradation

h b . I d' d23.?5 by Pseudomonas sp. ave een extensive y stu Ie -. The genetic information for hydrocarbon degradation in these organisms generally has been found to occur on plasmids. Numerical taxonomy has also been used to examine petroleum-degrading bacteria26

. Recently Rahaman et al. 27 reported 130 bacterial culture as crude oil degrades in Bombay high.

Factors influencing oil degradation

Nitrogen and phosphorous There is some confusion and considerable apparent

conflict in the literature regarding the limitation of petroleum biodegradation by available concentrations of nitrogen and phosphorous. Lepetit and Barthelem/

g reported that the concentration of

available nitrogen and phosphorus in water are severe limiting factors for microbial hydrocarbon degradation . Kinne/ 9

, however is of the opinion that nitrogen and phosphorus are not the limiting factor, since microorganisms require nitrogen and phosphorous for their incorporation into biomass and that the availability of these nutrients within the same

area as that of hydrocarbon is critical. Colwell et al. 30

concluded that Metula oil was degraded slowly in the marine environment most probably because of the limitations imposed by the relatively low concentrations of nitrogen and phosphorus availability. The cultures studies have indicated that the available concentra­tions of nitrogen and phosphorus severely limit the extent of hydrocarbon degradation of the most major oil spills. Rates of nutrient replenishment generally are inadequate to support rapid biodegradation of large quantities of oil. The addition of nitrogen and phosphorous containing fertilizers can be used to stimulate microbial degradation of hydrocarbon.

Oxygen As with nutrients, there has been controversy over

whether oxygen is absolutely required for hydrocarbon degradation or whether hydrocarbons are subject to anaerobic degradation. The recent literature by Grishchenkov3 1 and Zinjarde32 supports the view that anaerobic degradation by microorganisms at best proceeds at negligible rates in nature. The existence of microorganisms, which are capable of anaerobic hydrocarbon metabolism, has not been excluded l9

.

During storage of ' oil products, underground conditions are usually limited in oxygen and it is of special concern if hydrocarbon degradation is possible under anaerobic conditions. The initial attack on hydrocarbon requires oxygen, but for the subsequent steps, anaerobic processes may degrade partially oxygenated intermediates further. Under oxygen limited conditions and accumulation of degradation products in the form of fatty acids occur. It has been shown that the sulphate-reducing bacteria in the fuel , and even in a relatively static system. The microbes themselves can produce biosurfactants and gaseous by-products which carry up into fuel, increasing the surface area available for microbial activity.

r n fact, there have been several reports of isol ated microorganisms, which are capable of alkane dehydrogenation under anaerobic conditions 19. These organisms have enzymatic mechanisms, which should permit addition of water across the double bond, forming a secondary alcohol, and therefore permit anaerobic growth. In the case of Pseudomonas sp. strain studied by Senez and A7.0ul i 3

, the organi sms consumed oxygen when grown on heptane even though it had an n-heptane dehydrogenase enzyme. The importance of oxygen for hydrocarbon degradation is well indicated by the fact that the major degradative pathways for both saturated and aromatic

1016 INDIAN J EXP BIOL, SEPTEMBER 2'1(,3

hydrocarbons, involve oxygenases and molecular oxygen.

Degradation of hydrocarbons has been reviewed by Atlas 19, SRB can use a wide range of fatty acids including acetate , lactate, propionate, butyrate and fatty acids up to C IR and some phenyl substituted acids34

. The generally accepted view is that anaerobic degradation Of hydrocarbons is a very slow process as compared to aerobic degradation. Over very long periods, however, it might be significant. Reports on the anaerobic degradation in natural ecosystems have suggested that nitrate or sulphate could serve as I . I f 19 e ectron acceptors 111 pace 0 oxygen .

Temperature and pressure Schwarz et al. 35 cxamined the growth and

utilization of hydrocarbons at ambient and in situ pressure for deep-sea bacteria . The rate of hydrocarbon utili zation at hi gh pressurc and ambient temperatures were fo und to be signi fica ntly lower than the rates fo und under condi tions of ambient temperatures and atmospheric pressure, whereas 94% hexadecane was utili zed within 8 weeks at I bar while at 500 bars it took 40 weeks for similar degradation. it appears that oil , whi ch enters deep-ocean ~n vi ronmen ts, will be degraded very slowl y and persist for long periods of time. Biodegradati on ca n occ ur over a wide range of temperatures from below 0° to 70°C llJ.36.

Most hydrocarbon degrading microorganis m prefers a nea r neutral pH while source organi sm can tolerate ex treme va lues.

Consequences of oil degradation in fuel systems

Physical debris The most obv ious and recogni zabl e conseq uence of

microbia l acti vity is the formati on of visibl e so lids. These are the combinations of li ving and dead ce llul ar materi al, inorganic by-product and extraneous debri s and biologicall y generated membranous materi al. The 'class ic' hi stori cal problems are centered on Cladosporium resinoe, but many yeasts and bacteria can contribute signifi cantly too to thi s physical load. Th is material may block fuel lines, inj ectors, pi pes, filters and oil/water separators as well as adding potential corros ion problems.

Fuel turbidity/cloudiness For a fu el to be of marketable quality , it must be

clear and bright (C+B ). Microbial growth can often cause severe turbidity and cloudiness. Thi s arises in

one of two ways. Any mlxll1g of in terfaci al growth can often produce particles of such a density that they remain in components. The hydrocarbon range of gasoline, CS - C9 is less likely to be degraded, but kerosene with a hydrocarbon range of C IO-C IR is more susceptible3

? The preferenti al remova l of CIS - C35 n-alkanes relat ive to branched and cyc li c a lkanes is recogni zed as standard featu re in bio­degradation of crude oil s38

.39

. Degradat ion normally proceeds by a monotenninal attack wherein usuall y a primary alcohol is fo rmed followed by aldehyde and a mono carboxy li c ac id.

Chemical alteration of fu els Often linked with the increased corrosivity as

menti oned above are mi crobi all y produced by­products that can often change the ac tual chem ical propert ies of fu els in storage tanks and transport ing pipelines. Gaseous by-products from mi crob ial metaboli sm such as H2S, S01 and CO2 are often generated in such quantiti es that they can dissolve in the fuel, increasing the sil ver strip corros ivity index. The H2S generati on can also be a seve re hea lth hazard to the operatin g staff. Other metabolites , such as biosurfactants, can increase the emu ls i ficat ion of fu els.

Control of biodegl'adation of fu els

Physical cOlltrol Apart from maintaining fuels at temperatures

unsuitabl e for microbioiog ica l growth, whi ch is OnCil

very difficul t, the more obvious methoci of control is to eliminate water. by good house keeping techni ques, but thi s is often very difficu lt to ach ieve for the fo llow ing reasons: ;.... Ma ll Y fu els conta in a degree of dissolvcd or

chemi cally bound water, which can later condense out during temperature changes and form free mi crob iological 1 y a va i lable water.

);- At mospheric moi sture may of tell en ter the storagt' sys tems through breather vents , floati ng tan k tops, i neffecti ve seals etc .

);- Other systems may actuall y purge de livery lines with va ri ous sources of water, fo r example cleaning of pi g on muck collect ing tanks.

.,. Compl ete water removal may be very difficult du e to tank design etc. Thus, given that temperature control and water elimination , wh ich is oftcn imprac ti ca l or cost ly to implement, the alternati ve is to look fo r some means of chemi cal cont rol for

MUTHUKUMAR 1'1 01.: MICROBIOLOGICALLY INFLUENCED CORR OSION 10 17

the growth of fungi , yeasts and bacteri a, I.e. , a microbi ocide or microbios tal.

Chemical cOlltrol One of the main considerati ons in choosing

microbiocide is whether the aim is to treat the water phase, fuel ph ase or bo: h. There are advantages and disadvantages of treating either the water-fuel phase, but for long-term protection, a bioc ide that can treat the whole sys tem appears to be an ideal so lution.

Generally the bacteri al ph ysiology in oil pipeline undergoes in two ways:

( I ) Consumption or degradation of oil , (2) Conversion or storage or deposition of metals. Since these two processes are interlinked and dependent during the physiolog ical acti vity of microbes, the corrosion action w ill be high in oil pipelines. Hence, MIC is an important aspect In oil industry and it should be considered as a major factor by maintenance engineers.

Role of oil degradation on corrosion The biodegradati on of al i phatic and aromatic

hydrocarbons present in diese l oi I by PselidolllOIl (/S sp. was stud ied by Trzes icka-Ml ynarz and W ard.!!) and reported that degradation of al i phat ic than aromatic compounds occurred w ithin 20 days of incubation. Identica ll y, CECRI has noti ced that the rates of degradation of aliphati c hydrocarbons were found to be high when compared to the rates of degradati on o f aromatic hydrocarbons. The rate of addition of oxygen (consu mption of hydrogen) to vari ous strains is given below by Muthukumar et a14 1

. which was co ll ected from an oil pipeline in Northern Indi a.

Bmcefla sp. < Sltl{obaciflus sp. < Thiobacililts sp. < Moraxe fl a sp. < Galfioll e fla sp.

CECRl also observed4 1 th at, Brucella sp. was the most prevalent and dominant aromatic hydrocarbon degrad ing bacteri a. Similarl y, the works of Daughter et al. ,42 on the pol ycyclic aromatic hydrocarbon (PAH) degrad ing bacterial strains showed Pseudomonas pUlida , P .j7l1orescens, and P.aeruginosa isolated from the oil contaminated soil , which were further characteri zed for spec ifi c features regarding PAH degradati on. The soil fun gus Cfadophialopho ra sp. was also capable o f degrading alky lated benzenes (toluene, eth yl ben zene, xy lene) by a combination of assimilat ion and cometaboi ism. To luene and Eth y l benzene were used as sources of carbon and energy. The eth yl benzene was degraded by monooxygenase enzyme4

, . Besides RllOdococclIs rh odocl/J"OlIs S-2

produces ex tra cellular polysaccharides that help to sustain in aromatic fraction44

. Since Gallionella sp. ox idi zes ferrous ions into ox ide in presence of oxygen, it utili zes energy from carbon and hydrogen during oil degradation. Besides, it can be assumed that Brucella sp. help for the formation of more al iphatic protons in diesel which may be utili zed by Gallione fla sp.

Fe 2+ --7 Feh

(-CH z -CH , -) . . --7 (-O-CH ~-)Il - Bactenal metabolIsm

Internal corrosion control in oil pipelines Enormous amount of money is being spent every

year on prevention, monitoring, inspection, and land rcpair of the corrosion-related damages. Intern al corrosion contro l programmes usuall y involve chemica l trea tment w ith corrosIon inhibitors. Corrosion inhibitors are marketed iri several bas ic types, such as oil-soluble, water-di spersible, water-solubl e. limited­so lubility (gunkers), and volatile, etc., and each performs uniquely in different pipeline cond itions. It can be applied in a batch procedure where the persistent nature o f a heavy pro tec tive film may last fo r weeks or months. Or they can be continuously metered into the pipeline in low concentrations through a continuous injec tion programmer, in which a thin film is graduall y laid down and maintai ned overtime. The chemical s work very well. provided that they can reach the wall of the pi pe and form an effecti ve film.

Corrosion inhibitors are based on cation ic surfactant chemicals, which chemicall y bind to any negati vely charged surface. Included in thi s grouping are metal and corrosi on products such as iron carbonate, iron sulphide, iron ox ide, sand and clay. If deposits of dirt, corros ion products, and bacteri a are inside the pipe, they can both consume chemicals meant to treat the wa ll s o f the pipe, and prevent the chemical from contacting the wall s of the pipe beneath the depos its. For these reasons, pipel ines should be as cle:ln as poss ible when corrosion inhibitors are appli ed.

A pi gging programme is the most cost-e f fec ti ve and efficien t method of cleaning the pipc surface. for the appli ca ti on of liquid inhibitors.

Degl"adation of inhibitol's/biocides in petroleum pipeline

In general , organic filming inhibitors used in oil and gas producti on, transport and storage systems

1018 INDIAN J EXP BIOL. SEPTEMBER 2003

could be susceptible to microbial degradation during their use with a consequent loss in their efficiency for corros ion inhibition. Many of the misapplications of biocides/inhibitors occur because of the characteri stics of the biocide/inhibitors that are not considered before use. Genetic di versity and molecular evolution among microbial consorti a make them more potent and competent enough to transform or utilize the h ydrocarbon/i nhibi tors.

Benzo ic acid is read il y decomposed by the . . A' b I . 45 microorgani sm clI1ela acler ca coaceliCus , among

ot hers. The biodegradati on o f both n-al kane and several carboxylated cyc lo alkanes in o il sand tailings are also reported. Ingram46 descri bed yeast. that could degrade ben zo ic acid but onl y with the concomitant degradation of sugars. lone of the organisms were able to utili ze methy l p- hydroxybenzoate for growth but 1-1 ugo and Foster47 showed that Pse lldol/l ol1as aerugillosa NCTC 7244, an organism not examined

4 ~ by Beveridge and 1-1 ugo was ab le to do so. Beveridge and l-I art49 made further in ves ti gati ons

on the decompositi on or es ters of p-hydroxy benzoic acid by microorgani sms. They found that A lcalige// s

sp ., AerO///o//os sp. . Pselldolllo//as aerllg i//usa,

Pj 7l1orescell s and Bacilllls sp. were iso lated from a va riety of environment th at could degrade the este rs.

Soko lski cl al..'iO demonstrated the hydrol ys is or meth y I p-h ydrox ybenzoate by C/oslidi lllli r e.\i//(/c

(now HOJ"llloco//ic resillac) . The paren t ac id was decomposcd by all but one of the nine organisms tested by Beveridge and l-Iug04R bu t these workers round no allack upon the methy l ester. Sorb ic ac id is L1 sed as a preservati ve in the food and oil industry. It can be deg rackd to I . 3-pentad iene by certain moulds of the gcnus PellicilliulIl .

The path\vays di scussed so far have all dca lt w ith the decomposition of preservati ves under aerobi c conditions. In fact, many of the studies and ancill ary biochemica l investigations were carried out in air by Warburg respirometry. The anaerobic degradat ion or aromat ic compounds could be of importance in prese rved preparations packed in airtight containers. Anaerobic catabolism of these compounds has been reviewed by Slea t and Rob inson'; l . Of the compounds ciccomposed anaerob ica ll y, the follow ing preservati ves were identified: ben7.oate. benzy l alcohol, phenol. crcsols. cinnamic ac id and vanillic acid. The 0-. 1Tl- and p-hydroxybenzoic acids area also known to be metaboli zed alld it would be interes ting to see if their alkyl esters suffered decompos ition. It is clear that the ability to decompose compounds trad itionally regarded

as preservatives is a property of many microorganisms ranging from bacteria to fungi ancl this facet of microbial acti vity cannot be ignored during formul ation as a possible causati ve factor for microbiologica l spoil age.

One problematic area in treating gas lines is that stratifi cation of liquids in the line may occur. Therefore, the fl ow pattern or regimes must be considered when applying corros ion inhibitors. When multi phase conditions exist, liquids stratify along the pipe bottom, with water forming a separate layer beneath the hyd rogen liquids. Under these conditions, certain corrosion inhibitors do not corne into contact properl y with upper walls of the pipes, thereby leaving a good portion of it unprotected. The changes in !low regimes that develop due to changes in pipeline elevation or hindrance to the stratified tlow or slug flow when flu ids start flowing uph ill or downhill often result in the failure of inhibitor contacting the pipe wall s.

Corrosion fai I ure can occur when strati fi eation of pipeline liquids prevents the corrosion inhi bitor from reaching the upper wa ll s of the pipe. In oil lines, water can strati fy also at th e bOllom of the line w ith ve locit y is less than required to entrai n the water and sweep it through the system. Using o il so lu ble. water dispersible, f ilming amine- type corrosion inhi bi tors that can di sperse sufficientl y into stratifi ed water layers to prevent corrosion beneath th e water bes t inhibit s oil lines. Co tro l o f bacteria and bacteriall y induced corros ion in pipelines is anoth er area where chem ical app li cati on is enhanced greatl y when used in conjunction w ith pigg ing. Organic corros ion inhi bitors func ti on by chemi sorpti on of the molecule on a metalli c substrate, cO lllplex ing of the molecule w i th the meta l ion that remains in a so li d lalti ce , neutrali zing corrodent and or absorb ing the corrodenl. Bioc ides reduce the prolifera ti on of bacteri a in the product and on metals. M any of th e mi sapp li cations o f" bioc idesli nhi bitors occur mainl y because the characteri sti cs or bioc ides/inhibitors are not considered befo re use and thi s pl ays an important role of M I C5~ .

The petroleum industries are uni versa ll y fac ing a tough time due to corros ion in the pipel ine transporting the petroleum product. M any pipeline users li ke Indian Oil Corporati on, Bharath Petroleum Corporati on and Oil and Natu ral Gas Commiss ion are using many inhi bitDrs/bioc ides (Figs I &2) to overcome the microb ial corros ion in the storage tank s and in the pipeli ne transporting petroleum products. Many oil pipelines in India employ ing bioc ide/inhi bitors are fac i ng severe corros ion and microfoul i ng problems in their pipeline due to degradati on of" preservat i ves.

MUTHUKUMAR el al .. · MICROBIOLOGICALLY INFLUENCED CORROSION 1019

This article also presents the MIC and control measures associated with the selec ti on of vari ous inhibitors/biocides5J to make the oil f ield personnel. especiall y the non-biologists aware of the problems assoc iated with the applications of biocides even though the chemicals selected has been reported by biologists, to be effective against corrosion.

corros ion in condensing liquids at the top of the pipe. This can provide protection to the initial portion in the line where conden. at ion rates are high, although volatile inhibitors are generall y considered for their limited travel ability not go ing very far down the line.

Biocides Volatile inhibi tors, such as diethy lamine, can al so

be injected at the same time in order to prevent Biocides are the most underused, misunderstood.

and mi sapp lied chemica l products in the petroleu lll

Imidazolines /.f - CH2

R-C I , N-CH2

I

Primary Amine Rl

R-NH2

Diamines A - NH - C3HS - NH2

Amido-amines H I N - C2H4 - N - C2H4 - NH2 I I C::aO

I A

c-=-o I R

H H 0 0 H H

Dimerized amido-amines I '"...t II I C u. ~ C u. N _ H H-N-C2H4-N-C2H4-N-C-n -C-N- 2· ... - - 2 .... -,

I C=O I R

Dime( acid amido-amines ~ NH2- C2H4-N-C--A1

I

C=o I R

o 1\

H R4 ) ___ R3 --c - ~ - C2H4 - NH2

Oxyethylated primary amines

Alkyl pyridine

Quaternary amines

R" I

/c~ fi 9

R' - C"'" N /c - R'

R' may be CH3 10 C3H7 or higher

(CH3}3 - N+ - Ct -I R

Fig. I - Oi l I"ield corrosion inhibitors - Cat ionic molecular structures

H

1020 I DI AN J EX P BIOL. SEPTEMBER 2003

industry for many reasons. Bioc ides are used to combat a problem that is subtl e and difficult to detect. I n general , bioc icles are needed to control the acti vity of the bacteria in a system. However, biocides al one cannot sol ve a mi crobi olog ical problem.

Very few sample and reli able means of monitoring are available to the supplier or the end user, and the benefit s of bi ocide use tak e a long ti me to become ev ident. Finally, once bacteri a are well establi shed it is nearly impossible to control without dras tic

Dimer-trimer acids (C18 average)

Fatty acids

Naphthenic acids

----HR1----r ft

)---R2-_-C-OH o

J----R" ---~ - OH

o II

R-C-OH

Dodecyl benzene sulfonic acids

ft #,C-C, HO-~-Q C-R

H "C=C/

R= C12 branched or straight chained

Petroleum oxidates Petroleum-derived oxidates (from petrolatum, paraffin wax, lubricating oil, or fuel distillate) are complex mixture composed primarily of organic acids and esters, but also contain alcohols, ketones hydroxy and keto acids, estolides, lactides, and lactones.

Phosphate Esters of Ethoxylated alcohol

Other organic Acids I . Acc ti c 2. Hydroxyacctic .I. I3 cll zo ic

Fi g. 2 - Oi l f ield corrosion inhibi tors - A nionic molecular struc tures

M UTHUK UMAR el 01.: MICROB IOLOG ICALLY INFLUENCED CORROSION 102 1

measures54. Hence. identificati on of microbes and also

the role of inhibitors on mi crobi al growth are to be studi ed in detail.

Examples of chemicals used as fuel system biocides (fud+/or water soluble) • Methylene bi sthi ocyanate • Hexahydro-I ,3,5-tris (2- hydroxyeth yl)-S-triazine • Mi xture of 5-chloro-2-methyl-4-i sothi azolin-3-one

and 2-methyl-4-i sothiazol ine-3-one • Ethylene or diethylene glycol monomethyl ether • Mi xture of 4-(2-nitrobutyl ) morpholine and 4.4 ' -(2-

ethyl-2-nitromethylene-dimorpholine • Mi xture of 2' s-oxy-bis(4,4,6-trimethyl- 1 ,3,2-dioxa­

borinane) and 2, 2-( I-methyl-trimethylene di -oxy) bis-(4- methyl-I ,3,2-dioxaborinane)

• Methyl-I -(butyIcarbomoyl)-2-benzimidazole carba-mate-I-(2-hydroxyethyl-)-2-alkyl-( -C-1 8)-2-imidazo­line etc.

Monitoring program Initi al and continuous care IS better than later

preventi on beca use once metal is mi cro fouled, the fi lm can be eradicated onl y with the additi on of a microbi oc ides at very strong doses or by scrapping, which usuall y in volves much trained labours and high operational costs. Hence, it is necessary to formul ate a co ntinuous monitoring programme by weight loss assess ments and by mi crobiological analyses, if untreated water IS used. A simple monitoring programme is given below: • Chemi cal analys is of the water/oil used. • Sampling and identificati on of the microbial

population in the water/o il. • Identi fi cat ion of mi crobes that form sessi Ie

consorti a on the metals used in the site. • Detecti on of low veloc ity/stagnant points In the

now lines. • The quantity and the nutri ent contents of the water,

the interface betwee n inhibitor and biocide, the degradati on of inhi bitors have to be analysed for effecti ve usage of bioc ides.

• Selecti on of specifi c mi crobi oc ides with respect to the exact populati ons encountered in the site.

• Determi nation of exact conce ntrati on of microbioc ide at whi ch it ensures hi ghest percen t efficiency over sess ile bac teri a.

• If needed. di spersa nt ca n also be suppl emented with the microbi ocide.

• immedi ately aft er pigging the line, a hi gher concentrat ion of the mi crobiocide ca n be added

followed by peri odical additi ons at lower co ncentration (shoc k treatment). The quantity added should not be below the prescribed level. since a mi crob iocide at insufficient concentrati on promotes the microbial growth .

• Monitoring the magnitude of bacteri a before and after every four hours of biocide addition has to be carri ed out.

• Periodical monitoring of MIC by weight loss method/electrochemical probe technique is to be followed .

• The persistency and the leve l of the inhibitor/bi ocide should be checked by taki ng samples peri odicall y at vari ous pumping stations. In general, applied work towards the contro l of

MIC in oil pipeline is very much limited. Oil pipeline industri es require immedi ate solution to their problems of MIC rather than the mechani sms in vo lved. More research work on the insiru identifica tion of MIC and al so the ways to control MIC instantaneously is the need of the hour. A continuous monitoring programme must be es tabli shed in the industri es, which would be helpful in know ing the alarming concentrati on of mi crobes present in oil pipelines

References Sa ill ant A K .(personnel cO lllllluni ca tion). Insti tute of Enginee ring and Ocean Technology. Oil & Natural Gas Comilli ssion. Panve l 4 10 22 1, New Mu mbai .

2 Iverson N P. (cd) Advances in corros ion sc ience. Vol.2. (Plenu lll Press, New York) 1972. I .

3 Till er A K, Aspects of microb ial corros ion in corrosion process. App Sci Pub, 23 ( 1982) 185.

4 Ghi rose W C & Hirsch, A n ult ra structural studies of iron and manganese depos ition associated with extra-cellular polymers. Arch MicroiJ iol, 123 ( 1979) 2 13.

5 Li ttle B & Ray R. A rev iew of fu ngal innuencecl corrosion, Corrosioll Rei', 19 (200 I ) 40 I .

6 Vonwolzogcn kuhr C A H & Vander vlugt L K , DegraFiteering vangieb i fier also £Ieclrochelllislrv tlmeess il/ (II/aerobe grodel/. water (den Haag). 18 ( 1934) 147 Tr~ln s l ated in corros ion, 17 ( 196 1) 293.

7 Lec W. Z Lewandowski. S Okabe. W G Charackli s & R Avu, A corros ion of mild stecl underneath aerobic biofi lms containing sulphur reducing bJcteria. iJiofoul. 7( 1993) 197.

8 King R A & Mi ller J D A. Corrosion by SRB. Nalure 283 ( 197 1).

9 Ford T E and M itchell J S. Invo lvement of bacterial exopoly illers in biodetcri ora ti on of metals. IIIl Bindel iJideg. 7 ( 1990) 378.

10 Ive rson W P. M IC corrosion of metals. Ad\1 Appt MicroiJiol. 32 ( 1987) I.

II Obuekwe C O. M icrobial corrosion of crude oi l pipel ines. Ph D thesis. Universi ty of A lberta , Ed mondlon, 1981.

1022 INDIAN J EX P BIOL. SEPTEMBER 2003

12 Xu J S C. Dex ter & Luther III C W. Volta metric microe lectrodes for bi ocorros ion studi cs. J Sci EII~g Corr. 54 ( 1998) 8 14.

Ll Dex ter S C & M aruthailluthu S, Response of pass ivc alloys with n- and p- type pass ive films to manganese in bi ofilms. Corrosioll 200 1. Paper no. 01 267. Pub. NACE, Houston, Texas.

14 Shi X , A vc i R & Lewandoswski Z. Microbiologica lly depos ited m:lnganese and iron oxides on passi ve metal s -Their chcmi stry. distributi on and consequenccs for material s. Corrosioll. Paper No 02456 (2002).

15 Maruthamuthu S, Stella C. Jcyaprabha C. Mani A & Rengaswamy N S. Rolc of sulphate rcducing bacteria on COllusion process - A new mechanism. Pmc corrosion ({li d ils cOlll rol (Elscvier. NACE India Scction . Bombay). 19LJ7, 89 I.

16 ZoBe11 C E. Action of microorgani sms on hydrocarbon, B({ClerioIRcl'. 10 ( 1946) I .

17 Gibson D T. M icrobia l degradati on of arom ~lli c compollnd s. Sc icnce. 161 ( 1908) 1093.

18 ZoBelL C E. Microb ial degradati on o f oil. BaCferial Rcv. 2 ( 1973) 3.

19

20

2 1

22

') ~ _.'

25

26

27

A tl::!s R M. Microbi al deg rad ati on o f bydrocarbons and environllleillal perspec ti ve. Microbiol ReI'. 45 ( 198 1) 180. Barth a R & Atl as R M . The microbiology aquati c oil spi l ls. Adv Mlcm biol. 22 ( 1977) 685. Walke r. J D. Utili za ti on or mi xed bydrocarbon substrate by pctro leum degrad ing microorgani sms. J CCII Afifli M icmbiol 2 1 ( 1975)27. Walker J D. Petrol eulll degradati on by es tuarine microorg:.IIli sms. I lldiall J MicrolJiol. ( 1976) 197. Chakrabarty A . M . Geneti c hasis or the biodcgradat ion or sa li cy late, in Pselldollloll as J MicroiJ io l ( 1972) 8 15. Chakrabarty A . M , Chou G & Gun sa lus I C. Geneti c rcgulation or octane dissimilati on pl asmid in PsellllollloIlO.\'. Proc Acod Sci. USA, 70 ( 1973) 11 37. Dunn N W & Gunsa lus I C, Transmmisable pl as illid cod ing early enzymes of naphtbalene, ox idati on in PsclIdo /l /o ll as f1l1fida. J Nacleriol. 14 ( 1973) 974. A ustin 13 J, Caloillini s J. Walker .I D & Co lwe ll R R. Numeri ca l taxonomy and eco logy of petro leulll degrading bac teri a. API' Enviroll M icrobiol. 34 ( 1977) 60. Rahillan K S M . Thahira ·Rahman J. Lakshmanaperuillal samy P & Banat I M. Towards crri eient crude oil degradati on by a mixed bacteri al consortium. /J iores Tech. X5 (2002) 257.

28 Lcpet it J. & Barthelcmy H. Les hydroca rbon on mcracle problc me del' epuration des zoncs lillarates par les microorganisms. A 1111 I llS Puslcllr Par is. 11 4 (19()8) 149.

29 Ki nney D. Biodegradation or hyd rocarbons in the marine cnvironment. Appl EIII 'iroll Microbiol. 27 ( 196R) 125.

30 Colwe ll R R. Mil ls A L. Walker J D. Garcia P, Tell o & Campos V. Microbia l eco logy studi es or the M etull a spill in the m its or Mage llan . .I Fish Re.\' BOl/rd Call . 35 ( 1978) 573 .

31 Gri shehcnKov V G. Townsend R T. M cDonald T .I.

'I .L

Autenrieth R L. Bonner S & Boronin A M. Degradation of petroleum hyd rocarbon by facultati ve anaerob ic bacteri a uncle I' ae robi c and anaerobi c conditions, Process IJiochelll . 35 (2000) 8R9. Z injarde S S & Pant A A , Il ydroca rbon degraders from trop ica l environl1lents. Mar ill l! POllll l ioll /J IIII. 44 (2002) 118.

33 Sencz J C & Azoulay E. Dehydrogenat ion 01' pararfi nic hydrocarbon by res ting ce ll s and free extract or PseudOIlWllflS I/cn rg ill 0.\'(1 , Biochilll BioIJII)'.\· ACla. 47 1 ( I Y6 1) 307.

34 Widdel E, Degradation of hydrocarbons by sul phate. reducing bacteri a. J Appl nucleriol , ( 1980) 27 1.

35 Schwarz J R. Walker J D & Colwell R R. Decp·sea bacteria growth and utili zJtion or n-hcxa ne de ca ne at i ll si((( temperaturc and pressure. CUll J M icrobiol. 2 1 ( 1945) 6R2.

36 A tlas R M . in PClrolcrll1l microb iology (Macmi l lan . New YOI'k) 19R4 .

37 H i ll E C. Biocleg radati on of petroleu m products. In Pelmil' lIl11 lII icrobiologv. edited by R M At las (M acmi l lan Ncw York ). 1984. 579.

38 Cannan J. Biodegrad ati on or erude oi l ill reservoirs. in Ai/mll ce ill pel ro l £' 11111 geocilelllislr,l'. edited by J Brooks and D H. Welbe (Academic Press London). 19R4, 299.

39 Cannan J. BiOdegradati on of crude oi l in resc rvoirs. in Microbial pmhlcl/ls ill Ihe ojf:\'ho re oil illdllsfI ),. cd ited by E C Rirl, (Academic Press, UK ). 1987.48.

40 Tri 7.cs icka ml ynerz and ward 0 P, Call J M icrobiol. 41 ( 1995)470

4 1 Mut hukumar N. Syed Arir Su ltan J. Rap sekar A. el (/1 communica ted to 111 1. Biodel olld liior/eg. (2002 ).

42 Daughter F, E Dazicl. P li nell e. J G Bi sa i llon & Vi l lcmus. Comparati ve slUdy of rive polyaroilla tic hydl'Ocarbon degrading bacteri al strains iso lated from contami nated so i ls. Microbiologv. 43 ( 1997) 368.

43 Prenafeta-Bo ldu F X . Vervoort J, & Gvnesti.l n, J T C. J Appl l~'II V i roll Microb iol. 68 (2002) 2660.

44 Noriyuki Iwabuchi. Michi o Sunairi . M aka lO Urai. Ch iaki I toh, Hi roshi A nzai . Mutsuyasu Nakaj iona & Shigeak i Harayama,. Appl Enviroll Microbiol . 68 (2002) 2337.

45 Neidle E L & Omston L N. Benzoatc and muconatc structurJll y di ss imi lar rncta bol itcs induced ex press ion or cat A in AcineloiJacler calcoaccl ic lIs, .I liuclcriol. 169 ( 1987) 4 14.

46 Ingralll M , Benzoate re, istJnt yeasts . .I / ll'p l /Jacleriol. 22 ( 1959) 6.

47 Hugo W 13 & Foster J 1-1 S, Growth of PselldO/I/Olla.\' aerug ill osa in so lutions o f es ters of p-hyd rox ybenzo ic acid . .J Pha/'ll lOcol, 16 ( 19M) 209.

48 Beveridge E G & Hugo W B. T he res ist: lnce of ga lli c ac id and i ts alky l es ters to allack by bacteri :1 ab le to degrade aroillati c ring structures, Appll3acleriol. 27 ( 19M) 3()4.

49 Beveridge E G & Hart A . Thc utili zat ion for growth and the degradati on of p-hydroxybcnzoilte CSlc r, by b:lC teri a. 111 1

/Jiudc I('I'io /Jil l!. 6 ( 1970) 9. 50 Sokoloski W T. Chichester C G & Honeywe ll G E. Tbe

hydro lys is or IIlcth y l parah ydroxybenzoatc by Cladosporill lll res il/ {/e. Deve lop illd M icroh iol. 3 ( 1962) 179 .

5 1 Sleat R & Robinson J P. The bactcri ology o f anaerobic degraciJti on of aromati c compounds. J Ap,,1 IJIICf('l'iol. :; 7( 1984) 38 1.

52 Sm:lrt J S & Smith G L. Pigg ing and cheill ica l treatillen t for oi l Jnd gas pipelincs. Mal Per. 42 ( 1992) 47.

53 Treseder R S, Baboian R & Munger C G. NACE corrosion engineer' s reference book, Second Ed ition (NACE. 144() South Creek Dri ve Houston. T X) 199 1.

54 Boivin J, Oil indust ry bioc ides, Mm Per. 27 ( I ()9:;) 65.