SKR Term Paper-libre

8/11/2019 SKR Term Paper-libre

1/11

A REPORT SUBMITTED AT COMPLETION OF THECOURSE ON CORROSION & ENVIRONMENTAL

DEGRADATION OF MATERIALS (MT41013) .

CASE STUDY ON SOME OF THEMAJOR CORROSION CATASTROPHEIN THE HISTORY.

SUBMITTED BY:NITIN SINGH09MT3010


2/11

INTRODUCTION: While mankind has made remarkable progress in the last century,there have been some instances in the past where innocent human lives were consumeddue to some mishappenings as the unwanted byproduct of the same. Corrosion in itselfis not important, but the consequences of corrosion failure may well be. While corosionis almost always unwanted, the consequences of corossion are very costly. Littlesurprise, therefore, that a substantial engineering effort is directed towards its

prevention and control. In this report, those events are disucssed where corossion wasresponsible for taking the lives of hundreds of individuals. What lead to their occurrenceand their causes are discussed aswell .

BHOPAL GAS TRAGEDYThe Bhopal disaster, also referred to as the Bhopal gas tragedy, was a gas leak incidentin India, considered one of the world's worst industrial disasters. It occurred on the night

of 2 3 December 1984 at the Union Carbide India Limited (UCIL) pesticide plantin Bhopal, Madhya Pradesh. Over 500,000 people were exposed to methyl isocyanate gasand other chemicals. The toxic substance made its way in and around the shantytownslocated near the plant.Estimates vary on the death toll. The official immediate death tollwas 2,259.

[ The above pictures show the aftermath of the Bhopal Gas Tragedy where individualsdied within hours of the leakage of gas and its expansion in the atmosphere of Bhopal ]

FROM A CORROSION ENGINEERS STANDPOINT: The Bhopal disaster was theresult of a combination of legal, technological, organizational, and human errors. However,the immediate cause of the chemical reaction was the seepage of water (500 liters) into theMIC storage tank. Many investigators and researchers have agreed that corossion ofpipelins, values and other safety equipments as the main culprit for this catastrophy. Thefollowing evidences are presented to support the argument.

MIC was stored in three double-walled, partly buried stainless steel tanks codenamed 610, 611 and 619. While thousands slept in their huts around the pesticide
http://en.wikipedia.org/wiki/Gas_leakhttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/List_of_industrial_disastershttp://en.wikipedia.org/wiki/Union_Carbide_India_Limitedhttp://en.wikipedia.org/wiki/Pesticidehttp://en.wikipedia.org/wiki/Bhopalhttp://en.wikipedia.org/wiki/Methyl_isocyanatehttp://en.wikipedia.org/wiki/Methyl_isocyanatehttp://en.wikipedia.org/wiki/Bhopalhttp://en.wikipedia.org/wiki/Pesticidehttp://en.wikipedia.org/wiki/Union_Carbide_India_Limitedhttp://en.wikipedia.org/wiki/List_of_industrial_disastershttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Gas_leak


3/11

factory on the night of December 2/3, a skeleton staff of 120 workers inside the factoryended its evening shift around 10.45 pm and a new shift took over around 11 pm. Oneof the workers then noticed that the pressure in tank 610 the tank from which all theMIC finally escaped had risen from the two lb per square inch (psi), recorded by theearlier shift, to around 10 psi. Corresponding tank temperatures were not available asthey were not logged normally. The five-fold increase in pressure within an hour wasdismissed in the belief that the pressure recording instrument could be faulty. ShakilQureshi, the super isor o duty, said later, I stru e ts ofte did t ork. They gotcorroded. Crystals would form on them.

How the water entered the pipelines connected to the MIC containing stainless steeltank is altogether a different story, but its entry inside the MIC containing tanks couldhave been everted had the proper maintanince of the valves connecting the pipelines tothe tank being done. Carbon steel valves were used for this purpose. Carbon steelvalves easily corrode in acidic environment, which was actually happening in UCL

plant. Moreover, slip-blind plates which would have prevented the entry of waterthrough faulty valves were not installed. Once the water entered inside the MICcontaining tanks through faulty valves, the MIC found its way to escape from thetanks as well and hence to the atmosphere.

What happened inside the tank?The precise sequence of eve ts still re ai s o s ure. Car ides report has lai ed thatit was an unique combination of large amounts of water (120 to 240 gallons), higherthan normal amounts of chloroform in the stored MIC (several per cent instead of amaximum of 0.5 per cent), and an iron catalyst , that led to the violent reaction in MIC,stored at a higher than specified temperature. The heat released by the reactionbetween the water and MIC raised the temperature in the tank. Simultaneously, MICgot polymerised , the reaction being catalysed by iron resulting from the corrosion ofthe tank walls due to the high temperatures . Carbide claims that the corrosion rateincreased markedly because of the presence of an abnormally high level ofchloroform . The rapid release of carbon dioxide in large quantities then helped to buildup high pressures, which forced the foaming mass of chemicals out of the tank.

A file picture of the plant at Bhopal,showing the plight due to corrodedsections and components


4/11

The series of misforfortune did not stop here as the final blow to the safety of thepeople of Bhopal came when it was found out that Flare Tower could not be used asthe length of piping was corroded and and had not been replaced . The flare tower wasdesigned to burn off MIC escaping from the scrubber. The tower, however, wasinadequately designed for its task, as it was capable of handling only a quarter of thevolume of gas released, but still it could have lessened the amount of damage incurred to

human lives.

The Bhopal gas tragedy took place because of the corroded pipelines and valves.Despite the importance of corrosion prevention and control, many people in India stillprefer to ignore corrosion, which is considered to be a natural part of wear andtear. O e ight argue this as a result of UCLs egligie e for orrosio o trol or forthe value of human life, the relatives and friends of those who died are never going toreturn, added to this the environmental hazars that the MIC release had for years. Theabove amalysis of the Bhopal gas Tragedy proves how much corrosion control isimportant for an industry dealing with hazardous chemicals not just to avoid its ownloss but also the loss of innocent lives as well.

PRUDHOE BAY 2006 OIL SPILL

The Prudhoe Bay oil spill was an oil spill that was discovered in March, 2006 atapipeline owned by BP Exploration, Alaska (BPXA) in western Prudhoe Bay, Alaska .OnMarch 2, 2006 a BP Extration well pad operator discovered a leak in the transit linethat delivers oil to the trans-Alaska pipeline from Gathering Center 2 in the westernoperati g area of the gia t Prudhoe Bay oil field o Alaskas North Slope.The leakoccurred in the transit line segment between GC-2 and the point where the productionfrom Gathering Center 1 enters the line.BP launched an immediate response to what,with an estimated volume of around 200,000 gallons, proved to be the largest spill inthe history of Prudhoe Bay.

The cause of the leak became obvious within a few days of itsdiscovery: internal corrosion had caused a one-quarter-inch hole in the bottom of thetransit pipeline. The hole had formed in a section of line buried under what is termed acaribou crossing, a culvert designed to allow animals to cross over a pipeline asopposed to going under an elevated pipeline.The winter snow covered the leaking oil,so the spill remained undetected, probably for several days. It was odor the smell ofoil that ultimately exposed the leak to a worker.
http://en.wikipedia.org/wiki/Oil_spillhttp://en.wikipedia.org/wiki/Pipeline_transporthttp://en.wikipedia.org/wiki/BPhttp://en.wikipedia.org/wiki/Prudhoe_Bayhttp://en.wikipedia.org/wiki/Alaskahttp://en.wikipedia.org/wiki/Alaskahttp://en.wikipedia.org/wiki/Alaskahttp://en.wikipedia.org/wiki/Prudhoe_Bayhttp://en.wikipedia.org/wiki/BPhttp://en.wikipedia.org/wiki/Pipeline_transporthttp://en.wikipedia.org/wiki/Oil_spill


5/11

FROM A CORROSION ENGINEERS STANDPOINT: What happened in PrudhoeBay was Microbial Corrosion. All indications were that the corrosion that caused thehole in the transit line was biological in origin, caused by sulfate reducing bacteriainside the pipeline . The corrosion pits confirmed this and also the way in which thecorrosion in the pipeline accelerated over time was characteristic of the way in whichmicrobiological corrosion develops, as the bacteria grow and multiply.

The bacteria forms in water, so that problems associated withmicrobiological corrosion were suspected to be associated with the water carryingpipelines, such as the lines which were used for waterflood operations .

Transit lines less corrosion prone : BP had viewed oil carrying transit lines, suchas the line from GC-2 that developed a leak, as much less susceptible to corrosionthan a water bearing line. But the company had regularly monitored the Prudhoe Bayoil transit lines for internal corrosion using two techniques: ultrasonic testing and theuse of corrosion coupons.

Ultrasonic testing involves the use of an ultrasonic device to measurethe thickness of the pipeline wall a thinning of the wall indicates the presence ofcorrosion. A corrosion coupon is a small metal plate placed inside the pipeline andinspected for corrosion every 90 days

For straight 29 years, BP noted nothing of significance. It was only in fallof 2005 that evidence of increasing corrosion activity started to appear. The increasingamount of corrosion found in the fall of 2005 caused BP to step up the inspectionprogram on the pipeline the company increased the number of inspection points,increased the frequency of inspections at some points and scheduled a smart piginspection for the summer of 2006, according to the BP report.

However, an inspection of the line after the March2006 leak showed evidence of high rates of corrosion, even in place that had beenfree of corrosion in the fall 2005 inspection. Clearly, there had been an exponentialgrowth of corrosion, culminating in the hole that caused the oil spill.

Why did the corrosion accelerated so rapidly?BP investigation report theorized two main factors that came together at the sametime.

The first factor related to corrosion inhibitors . BP added about 3 million gallonsper year of these inhibitors to Prudhoe Bay production fluids; the fluids carried theinhibitors into production facilities such as GC-2. But the corrosion inhibitorsappeared to have been present in relatively low concentrations in the GC-2production facilities, when compared with the other Prudhoe Bay facilities. It wasthus concluded that the fluids passing down the GC-2 transit line from GC-2 containedonly small amounts of the inhibitors, thus providing opportunities for corrosion-causing bacteria to grow. The corrosion inhibitor shortfall may have occurred


6/11

because GC-2 was the only facility at Prudhoe Bay which processed viscous oil. Theviscous oil production introduces more solids into the processing facilities thantraditional production and BP thought that these additional solids may have adsorbedsome of the inhibitor.

The second possible factor was the relatively low flow rate in the GC-2transit line, upstream of GC-1. With Prudhoe Bay production in decline, the transit line

was carrying much smaller volumes of oil than the line was designed to handle theresulting sluggish flow may have enabled an increased build up of water in the line andprovided an environment conducive to the incubation of bacteria. There was much lesscorrosion downstream from GC-1, where the addition of the fluids from GC-1 wouldhave increased flow rates in the line.

There was also a build up of solids in the GC-2 transit line over a period ofseveral years, as sediment carried by the fluids from the GC-2 processing facilitiessettled in the pipeline. It is not possible to discount the possibility that these solidscontributed to the corrosion.

[A file photograph showing clean up crews recovering more than 19,000 gallons of

crude oil leaked from athe pipeline leaken in Prodhoe bay]

Summary of what happened in Prodhoe Bay : Sulphate reducing bacteria (SRB)are small anaerobic microorganisms. When conditions are right they can multiply tothe level of millions of cells per gram and generate significant quantities of hydrogensulphide (H2S). The H2S together with the stagnant conditions formed by the colonyon the pipewall lead to enhanced pitting corrosion rates . The corrosion in thesespecial cases caused by microbials is termed as Microbial Corrosion .


7/11


8/11

At the origin of the accidental sequence, the deficiency of Reactor no. 5 stemmed fromcracking corrosion caused by nitrates contained in the water used in the past to spraythe small cyclohexane leaks, in an effort to limit the risk of ignition. This water hadpenetrated into the insulation and, during evaporation, deposited nitrates onto theequipment steel.

The cause of the leak on Reactor no. 5 should have been analyzed priorto any unit reactivation and the other reactors should have been verified with respectto the degradations sustained by Reactor no. 5. Such an approach however would haverequired shutting down the plant for a few days; the concern over minimizing plantdowntime and production losses actually motivated the stopgap configuration thateventually gave rise to the accident.

The crack in Reactor no. 5, which served as the source of the accidentalsequence, stemmed from corrosion caused by spraying the reactor with drinking water(hence high in nitrates) in order to dilute cyclohexane discharge and limit the risk ofignition. The crack in Reactor no. 5 indicates that drinking water contains nitratescapable of causing steel corrosion when under tension. Thus , Nitrate-induced corrosion was held liable for Flixborough disaster.

GUADALAJARA SEWER EXPLOSIONS

The 1992 Guadalajara explosions took place on April 22, 1992, in the downtown districtof Analco. Numerous gasoline explosions in the sewer system over four hoursdestroyed 8 kilometers of streets . Officially, by the Lloyd's of London accounting, 252people were killed, nearly 500 injured and 15,000 were left homeless

[ Aftermath of the Guadalajara sewer explosions]
http://en.wikipedia.org/wiki/Guadalajara,_Jaliscohttp://en.wikipedia.org/wiki/Gasolinehttp://en.wikipedia.org/wiki/Sanitary_sewerhttp://en.wikipedia.org/wiki/Sanitary_sewerhttp://en.wikipedia.org/wiki/Gasolinehttp://en.wikipedia.org/wiki/Guadalajara,_Jalisco


9/11

FROM A CORROSION ENGINEERS STANDPOINT: The sewer explosion was tracedto the installation of the water pipe by a contractor sveral years before the explosionswhich leaked water on a gasoline line lying underneath. The cathodically protectedsteel gasoline pipeline had a hole inside a cavity and an eroded area, all in longitudinaldirection. A second wall did not perforate the internal wall. The galvanized water pipe obviously had suffered stray current corrosion effects that were visible in pits ofdifferent size ( see the picture below ).

The corroded water pipes lines lead to the leakage of water from them which furtherbecome responsible for the aqueous corrosion of gasoline pipelines . This lead toleakage of gasoline into the sewers.

CARLSBAD PIPELINE EXPLOSIONAt 5:26 a.m., mountain daylight time, on Saturday, August 19, 2000, a 30-inch diameternatural gas transmission pipeline operated by El Paso Natural Gas Company (EPNG)ruptured adjacent to the Pecos River near Carlsbad, New Mexico. The released gasignited and burned for 55 minutes. Twelve persons who were camping under a

Pits formed in waterpipelines due to straycurrent corrosion


10/11

FROM A CORROSION ENGINEERS STANDPOINT:Post-accident on sight inspection - The force of the rupture and the violent ignition ofthe escaping gas created a 51foot-wide crater and ejected three large pieces.Investigators visually examined the pipeline that remained in the crater as well as thethree ejected pieces. All three ejected pieces showed evidence of internal corrosion damage, but one of the pieces showed significantly more corrosion damage than the

other two. Pits were visible on the inside surface of this piece, and at various locations,the pipe wall evidenced significant thinning. At one location, a through-wall perforationwas visible. No significant corrosion damage was visible on the outside surfaces of thethree pieces or on the two ends of the pipeline remaining in the crater.

Internal Corrosion in line 1103 - Interconnecting pits were observed on the inside ofthe pipe in the ruptured area of line 1103. Typically, these pits showed the striations andundercutting features that are often associated with microbial corrosion . A pit profileshowed that chloride concentration in the pits increased steadily from top to bottom.

Increased chloride concentration can result from certain types of microbial activity . Allfour types of microbes (sulfate reducing, acid-producing, general aerobic, and anaerobic)were observed in samples collected from two pit areas in the piece of line 1103 whereinternal corrosion was discovered after the accident about 2,080 feet downstream of therupture site. Though the individual contribution of various microbes in the corrosionprocess could not be estimated, the damage morphology and the corrosion productanalyses data suggest that microbiological activity contributed to the corrosion process.

Dissolved O 2 in an electrolyte could cause pitting by creatingconcentration cells . CO2 is soluble in water and will form carbonic acid, which is corrosiveto carbon steel.

When dissolved in water, H 2S forms a weak acid that could corrode carbon steel .In combination with dissolved O 2, it could cause pitting. Though generally present in lowconcentrations, these potentially corrosive constituents were present in the gas that wasbeing transported in line 1103. Also, upset conditions occasionally increased theconcentrations of these constituents in the transported gas.

Chlorides were observed in all corrosion product/deposit samples.Anions, such as chloride, cause pitting and, typically, chloride concentration in a pit maybe much higher than the chloride concentration outside the pit (bulk concentration).

Chemical analyses showed that the pH ( 6.7-6.8 ) of the liquid collected at thePecos River compressor station plant inlet separator scrubber was more acidic than thepH (8.2 ) of the liquid collected at Keystone compressor station inlet scrubber. Also, thematerial collected at line 1100 and 1103 pig receivers ( pH 6.2-6.3 ) and the inside materialcollected from a low spot on line 1103 west of the rupture (pH - 6.4) were more acidicthan the material collected near the siphon drain area of the line 1103 drip ( pH 8.9 ). Theobserved low pH in the samples could be a result of dissolved CO 2, and/or H 2S in thewater, and/or intrusion of low-pH ground water into the gas supply. Typically, acidic( pH7 ).


11/11

Thus, water and contaminants such as chlorides, O 2 , CO2 , H 2S and microbes alllikely contributed to the observed corrosion damage.

CONCLUSION: While the occurrence of corrosion and environmental degradation ofthe materials seems inevitable, It can be avoided to certainly a large extent. The timelymeasures taken on the part of engineers can result not only in cost reduction of theindustry or organization but can also become a saving cause for hundreds of valuablehuman life. Histroy always has its way of delivering lessons, time has come that adeveloping contry like ours takes steps at every possible level to reduce the risk of anycatastrophe occuring due to corrosional degradation .

SKR Term Paper-libre

Documents

Transcript of SKR Term Paper-libre