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Corrosion inspection and monitoring pdf

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counted as direct costs. The NACE. Corrosion Monitoring, Detection, and. Measurement. Equipment manufacturers are helping organizations control costs. Fig. This text is broken into five chapters. The first chapter,. Corrosion and Its Cost In a Modern World, introduces the topic of corrosion of metals and highlights issues. Index. Corrosion: importance of corrosion. Corrosion monitoring: ER prototype. 2 ·. Corrosion inspection: Active thermography.


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Strategic corrosion inspection and monitoring can improve asset management and life cycle assessment and optimize operational budgets. Corrosion Inspection and Monitoring WILEY SERIES IN CORROSION caite.infon Revie, Series Editor Corrosion Inspection and Monitoring · Pierre R. Roberge. Request PDF on ResearchGate | Corrosion Inspection and Monitoring | Half TitleWiley Series PageTitleCopyrightContentsPreface.

The subsequent corrosion attack is the result of hydromechanical effects from liquids in regions of low pressure where flow velocity changes, disruptions, or alterations in flow direction have occurred. Some general guidance in carrying out failure analysis is also provided since such process can generate very valuable information for subsequent inspection tasks. Should include all the on-line data as well as the data collected manually coupons etc. Wiley-Interscience, ; pp. It can also occur under scale and surface deposits and under loose-fitting washers and gaskets that do not prevent the entry of liquid between them and the metal surface. After weighing, the specimens should be examined for localised attack pitting.

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Skip to Main Content. Corrosion Inspection and Monitoring Author s: Pierre R. First published: Print ISBN: About this book The comprehensive reference on modern techniques and methods for monitoring and inspecting corrosion Strategic corrosion inspection and monitoring can improve asset management and life cycle assessment and optimize operational budgets.

It covers: ROBERGE , PhD, a full professor at the Royal Military College of Canada, has conducted research on the development of accelerated tests for the characterization of the corrosion resistance of metallic materials, the performance of materials in service, and the production of energy with electrochemical power sources.

He is the author of numerous articles and papers and three books on corrosion engineering and testing. Free Access. Summary PDF Request permissions. In the following example, the deformation due to the corrosion of aluminum in lap joints of commercial airlines is accompanied by a bulging pillowing between rivets, due to the increased volume of the corrosion products over the original material. This problem was said to be the primary cause of the Aloha incident in which a year old Boeing , operated by Aloha airlines, lost a major portion of the upper fuselage Fig.

The Fig. Courtesy Wayne Senick Termarust Technologies www. Corrosion Factors 15 Fig. Photograph of the Boeing operated by Aloha airlines that lost a major portion of the upper fuselage in The prevalent corrosion product identified in corroded fuselage joints is hydrated alumina, Al OH 3 , with a particularly high volume expansion relative to aluminum as shown in Fig.

Corrosion Inspection and Monitoring - PDF Free Download

This build-up of voluminous corrosion products can lead to an undesirable increase in stress levels near critical fastener holes Fig. Material Factor In environments that can be reasonably well defined, unexpected corrosion may result from lack of definition of the material itself.

Defining a material by its specification is often, and especially for new designs, quite inadequate.

Pdf and monitoring corrosion inspection

Relative volume of aluminum corrosion products. Corrosion Factors 17 Fig. Analysis sequence for determining materials at a location for analysis LA matrix. A brief explanation of the individual elements of the process illustrated in Fig. The overall region where maximum pitting and biofouling occur is evidence of the passive state of the alloy.

However, a less obvious, but most important, consideration in defining materials is defining the compositions of their grain boundaries, since many degradation reactions either follow grain boundaries or are initiated at grain boundaries. The deficient alloy in this area can then be attacked so severely in certain environments that the entire grain is surrounded and will fall from the structure Fig.

Welding of the unstabilized stainless steels can be a major source of this problem Fig. The behavior of copper—nickel alloys in seawater Corrosion Factors 19 Fig. This particular problem occurred on Type H stainless steel after 7 years of service. This particular stainless steel is not recommended for welding. Courtesy Kingston Technical Software. The commonly accepted mechanism attributes intergranular corrosion to a difference in potential between a chromium-depleted zone at the grain boundaries and the chromium-rich central zones of the grains Fig.

Weld decay zone as a function of the welding temperature of stainless steel. Sensitization of stainless steel in the heat adjacent zone. Degradation reactions are also affected by the presence and distribution of second phases whether at grain boundaries or distributed through the grains. Such second phases are often loci of pitting or, when lined up, may provide preferential paths for chemical degradation.

Second phases also produce certain embrittlement, such as the formation of sigma phase in Fe—Cr base alloys. Iron—chromium phase diagram. This phase is important because its formation usually results in a reduction in the mechanical properties and corrosion resistance of the alloy.

Many wrought aluminum alloy products leave highly directional grain structures. Almost all forms of corrosion, even pitting, are affected to some degree by this grain directionality. However, highly localized forms of corrosion, such as exfoliation and SCC that proceed along grain boundaries, are highly affected by grain structure.

Long, wide, and very thin pancake-shaped grains are virtually a prerequisite for a high degree of susceptibility to exfoliation. Such products are highly anisotropic with respect to resistance to SCC Fig. Resistance, which is measured by magnitude of tensile stress required to cause cracking, is highest for aluminum alloys when the stress is applied in the longitudinal direction, lowest in the short-transverse direction, and intermediate in other directions.

These differences are most noticeable in the more susceptible tempers, but are usually much lower in tempers produced by extended precipitation treatments, such as T6 and T8 tempers for 2xxx alloys and T73, T, and T76 tempers for 7xxx alloys Schematic representation of the three-dimensional 3D grain structure typically present in rolled aluminum plates. SCC of alloy — plate. Shaded bands indicate combinations of stress and time known to produce 5CC in specimens intermittently immersed in 3.

Point A is minimum yield strength in the long-transverse direction for a mm thick plate During the design and prototyping processes, it is not uncommon for materials to be changed for reasons of performance, compatibility, or cost. When such changes occur, the materials should be reevaluated according to the steps defined in this section. Actually, something can and should be done to prolong the life of metallic structures and components exposed to the environments.

As products and manufacturing processes have become more complex and the penalties of failures from corrosion, including safety hazards and interruptions 1. Strategic Impact and Cost of Corrosion Damage 23 in plant operations, have become more costly and more specifically recognized, the attention that is being given to the control and prevention of corrosion has increased. This study attempted to measure the total costs associated to corroding components by summing up the cost for both the owner and operator direct cost and for the users indirect cost.

Corrosion costs studies of various forms and importance have since then been undertaken by several countries including, the United States, United Kingdom, Japan, Australia, Kuwait, Germany, Finland, Sweden, India, and China Several studies separated the total corrosion costs into two parts: The portion of the total corrosion cost that could be avoided if better corrosion control practices were used.

Costs where savings required new and advanced technology currently unavoidable costs. Most studies have categorized corrosion costs according to industrial sectors or to types of corrosion control products and services. All studies have focused on direct costs even if it has been estimated that indirect costs due to corrosion damage were often significantly greater than direct costs.

Indirect costs have been typically excluded from these studies simply because they are more difficult to estimate. Potential savings and recommendations in terms of ways to realize savings from corrosion damage were included in most of the reports as formal results or as informal directions and discussion.

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Two of the most important and common findings were 1. Better dissemination of the existing information through education and training, technical advisory and consulting services, and research and development activities. The opportunity for large savings through more cost-effective use of currently available means to reduce corrosion.

An amendment for the cost of corrosion was included in the Transportation Equity Act for the twenty-first century, which was passed by the U. The amendment requested that a study be conducted in conjunction with an interdisciplinary team of experts from the fields of metallurgy, chemistry, economics, and others, as appropriate.

The first approach followed a method where the cost was determined by summing the costs for corrosion control methods and contract services. The costs of materials were obtained from various sources, such as the U. Department of Commerce Census Bureau, existing industrial surveys, trade organizations, industry groups, and individual companies. Data on corrosion control services, such as engineering services, research and testing, and education and training, were obtained primarily from trade organizations, educational institutions, and individual experts.

These services included only contract services and not service personnel within the owner—operator companies. The second approach followed a method where the cost of corrosion was first determined for specific industry sectors, and then extrapolated to calculate a national total corrosion cost.

Data collection for the sector-specific analyses differed significantly from sector to sector, depending on the availability of data and the form in which data were available.

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In order to determine the annual corrosion costs for the reference year of , data were obtained for various years in the surrounding decade, but mainly for the years — A breakdown of these costs by individual sectors is shown in Fig. Since not all economic sectors were examined, the sum of the estimated costs for the analyzed sectors did not represent the total cost of corrosion for the entire U. By estimating the percentage of U.

GNP for the sectors for which corrosion costs were determined and by extrapolating the figures to the entire U. Corrosion costs breakdown across industrial sectors. Lifetime Prediction of Materials in Environments. Revie RW, ed.

New York: Wiley-Interscience, ; pp. Preventing Corrosion under Insulation. Chemical Engineering ; 97— Microbial Aspects of Metallurgy. American Elsevier, Corrosion ; Corrosion Testing Made Easy: Erosion-Corrosion Testing. Houston, TX: NACE International, Handbook of Corrosion Engineering. McGraw-Hill, Water Corrosion. Corrosion Basics. NACE International, ; — Iron and Steel. Uhlig HH, ed. The Corrosion Handbook. Corrosion Basics—An Introduction. Corrosion Science ; Corrosion control on aging aircraft: What is being done?

Materials Performance ; Materials Evaluation ; Corrosion of Aluminum and Aluminum Alloys. Metals Handbook: Corrosion Vol. Metals Park, OH: American Society for Metals, ; pp. The Cost of Corrosion in the United States. Chemical and Engineering News ; Chapter 2 Corrosion Detectability 2. Defects And Failures 2. What Is a Defect? What Is a Fault? What Is a Failure? Functional Failure 2. Potential Failure 2. What Are the Consequences of a Failure?

Safety Consequences 2. Operational Consequences 2. Nonoperational Consequences 2. Hidden Failure Consequences 2. Corrosion Failure Examples 2. Bhopal Accident 2. Carlsbad Pipeline Explosion 2. Guadalajara Sewer Explosion 2.

Inspection and pdf corrosion monitoring

El Al Boeing Crash 2. Nuclear Reactor With a Hole in the Head 2. Sinking Ships 2. SCC of Chemical Reactor: The Flixborough Explosion 2. Swimming Pool Roof Collapse 2. Age-Reliability Characteristics 2. Probability of Failure 2. Probability of Detection 2. Forms of Corrosion 2.

Uniform Attack 2. Pitting Corrosion 2. Crevice Corrosion 2. Galvanic Corrosion 2. Flow Influenced Corrosion 2. Fretting Corrosion 2. Intergranular Corrosion 2.

Dealloying 2. Environmental Cracking 2. Corrosion Fatigue 2. Loss of Ductility and Strength 2. Hydrogen Blistering 2. High-Temperature Effects References 2. Whereas Chapter 3 introduces management methodologies that have been created to reduce these consequences to manageable levels, this chapter discusses the possible types of corrosion damage that exist, their initiation and propagation rates, and their detectability.

A universal representation describing the interactions between defects, faults, and failures of a system is shown in Fig. The arrows in this figure imply that quantifiable relations possibly exist between a defect, a fault, and a failure. Consequence of a failure Failure Mode: Interrelation among defects, failures, and faults. Defects And Failures 29 2. In materials science, a defect is any microstructural feature representing a disruption in the perfect periodic arrangement of atoms in a crystalline material.

These fundamental defects and their distribution in a given material can have a great importance on the overall properties of that material. While such defects do not constitute flaws in the normal sense of the word they can nonetheless serve as anchors for the initiation of actual faults and subsequent failures.

There are four fundamental defect types: Point defects: Point defects or sites are vacancies that are usually occupied by an atom, but are presently unoccupied. If a neighboring atom moves to occupy the vacant site, the vacancy moves in the opposite direction to the site that used to be occupied by the moving atom.

The stability of the surrounding crystal structure guarantees that the neighboring atoms will not simply collapse around the vacancy. In some materials, neighboring atoms actually move away from a vacancy, because they can better form bonds with atoms in the other directions.

Line defects: Line defects are dislocations around which some of the atoms of the crystal lattice are misaligned. There are two basic types of dislocations: Dislocations are caused by the termination of a plane of atoms in the middle of a crystal.

In such a case, the surrounding planes are not straight, but instead bend around the edge of the terminating plane so that the crystal structure is perfectly ordered on either side.

Planar and surface defects: An important planar defect example is the grain boundaries that occur where the crystallographic direction of the lattice abruptly changes. This commonly occurs when two crystals begin growing separately and then meet. Many types of corrosion discussed later are directly related to the nature and geometry of grain boundary structures. Bulk defects: An example of bulk defects are voids where there are simply no structural atoms.

Another example are impurities that can cluster together to form small regions of a different phase, e. Impurities and precipitates also play an important role in the corrosion resistance of metallic materials. The growth of a defect into what becomes a fault or a faulty component really depends on a multitude of factors that include predominantly the type of corrosion that is indeed progressing, as will be described later in the chapter.

In the faulttree analysis context, the fault event of a component is defined as a state transition from the normal state to a faulty state of that component. These state transitions 30 Chapter 2 Corrosion Detectability are irreversible, which means that a faulty state does not return to the intended state even if the influences that caused the fault event in the first place disappear. Corrosion processes are irreversible by nature since they change a metal into more stable oxidized states.

In fact, the corrosion products can only be returned to metals by complicated and energetically expensive processes that eventually end up with molten metals. However, not all corrosion processes lead to faulty systems if, for example, a corrosion allowance has been included in the system at the design stage. Some clear examples of corrosion faults can be found in electronic components where even very small amounts of surface corrosion can drastically alter the intended behavior of components.

Connector corrosion is well understood as an age-related problem that contributes greatly to electrical wiring failures. Connector corrosion is also the prime suspect in several military and commercial aircraft incidents and accidents. Fretting corrosion in electronic components, for example, is the result of flaking of tin oxide from a mated surface on tin-containing contacts.

The problem becomes more frequent as tin is used to replace gold as a cheaper plating route. The only solution for this hard-to-diagnose, and often intermittent, problem is to replace the faulty part.

One problem of this type discovered by an air force corrosion engineer was the corrosion of tin-plated electrical connector pins mated with gold-plated sockets. Fretting corrosion between these very small contacts appears to have been implicated in at least six F fighter aircraft crashes when their main fuel shutoff valves closed uncommanded 1.

Figure 2. Courtesy David H. Defects And Failures 31 Fig. Courtesy David A. Another problem in which a microscopic quantity of corrosion products can create havoc in a complex electronic system is the formation of dendrites across circuit channels.

In the presence of moisture and an electric field, metals in their ionic state can migrate to a cathodically negatively charged surface and plate out, forming dendrites. Dendrites can be silver, copper, tin, lead, or a combination of metals. The dendrites grow and eventually bridge the gap between the contacts, causing an electric short and possibly arcing and fire.

Even a small volume of dissolved metal can result in formation of a relatively large dendrite Fig. Dendrite growth can be very rapid. Failures have been known to occur in 2.

A failure is an unsatisfactory condition or a deviation from the original condition which is unsatisfactory to a particular user. The determination that a condition is unsatisfactory, however, depends on the failure consequences in a given operating context 2. The determination will therefore vary from one operating organization to another. Within a given organization, however, it is essential that the boundaries between satisfactory and unsatisfactory conditions be defined for each item in clear and unmistakable terms.

The judgment that a condition is unsatisfactory implies that there must be some condition or performance standard on which this judgment can be based. However, an unsatisfactory condition can range from the complete inability of an item to perform its intended function to some physical evidence that it will soon be unable to do so.

For maintenance purposes, failures must therefore be further classified as either functional failures or potential failures. Functional Failure A functional failure is the inability of a system to meet a specified performance standard.

A complete loss of function is clearly a functional failure.

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However, a functional failure also includes the inability of an item to function at the level of performance that has been specified as satisfactory. To define a functional failure for any component or system, a clear understanding of its functions is required.

It is extremely important to determine all the functions of an item that are significant in a given operational context, since it is only in these terms that its functional failures can be defined.

Potential Failure Once a particular functional failure has been defined, some physical condition may often be identified to indicate that this failure is imminent. Under these circumstances it might be possible to remove the component or system from service before the occurrence of a functional failure.

When such conditions can be identified, they are defused as potential failures. A potential failure is an identifiable physical condition that indicates when a functional failure is imminent. The fact that potential failures can be identified is an important aspect of modern maintenance theory, because it permits maximum use of each system without the consequences associated with a functional failure.

Units are removed or repaired at the potential failure stage, so that potential failures preempt functional failures. For some items, the identifiable condition that indicates imminent failure is directly related to the performance criterion that defines the functional failure. The ability to identify either a functional or a potential failure thus depends on three factors: Clear definitions of the functions of a component or system as they relate to the equipment or operating context in which the item is to be used.

A clear definition of the conditions that constitute a functional failure. Defects And Failures 33 3. A clear definition of the conditions that indicate the imminence of this failure.

In other words, it is important not only to define the failure, but also to specify the precise evidence by which it can be recognized. Failure analysis is the traditional method of relating a failure to its consequences.

These may range from the modest cost of replacing a failed component to the possible destruction of a piece of equipment and the loss of lives.

The consequences of a failure determine the priority of the maintenance activities or design improvement required to prevent its occurrence. The more complex a piece of equipment is, the more ways there is by which it can fail. Failure consequences can be grouped into the four categories described in the following sections 2. Safety Consequences The first consideration in evaluating a failure possibility is safety, that is, does the failure cause a loss of function or secondary damage that could have a direct adverse effect on operating safety?

A critical failure is any failure that could have a direct effect on safety. Note, however, that the term direct implies certain limitations. The impact of the failure must be immediate if it is to be considered direct. In addition, these consequences must result from a single failure and not from a combination of this failure with one that has not yet occurred.

If a failure has no evident results, it cannot, by definition, have a direct effect on safety. Not every critical failure results in an accident. However, the issue is not whether such consequences are inevitable, but whether they are possible.

Safety consequences are always assessed at the most conservative level, and in the absence of proof that a failure cannot affect safety, it is classified, by default, as critical. In the presence of a possible critical failure, every attempt should be made to prevent its recurrence.

Often redesign of one or more vulnerable items is necessary. However, the design and manufacture of new parts and their subsequent incorporation in in-service equipment can take months, and sometimes years. Hence, temporary measures are often required in the meantime. Operational Consequences Once safety consequences have been ruled out, a second set of consequences must be considered, that is, has the failure any direct adverse effect on operational capability?

A failure has operational consequences whenever the need to correct a failure disrupts planned operations. Thus operational consequences include the need 34 Chapter 2 Corrosion Detectability to abort an operation after a failure occurs, the delay or cancellation of other operations to make unanticipated repairs, or the need for operating restrictions until repairs can be made.

A critical failure can, of course, be viewed as a special case of a failure with operational consequences. In this case, the consequences are economic and consist of imputed cost of lost operational capability. Nonoperational Consequences There are many kinds of functional failures that have no direct adverse effect on operational capability.

One common example is the failure of a navigation unit in a plane equipped with a highly redundant navigation system. Since other units ensure availability of the required function the failed unit can be replaced at some convenient time.

Thus the costs generated by such a failure are limited to the cost of corrective maintenance. Hidden Failure Consequences Another important class of failures with no immediate consequences consists of failures of hidden-function items. By definition, hidden failures have no direct adverse effects, that is, if they did these failures would not be hidden.

However, the ultimate consequences can be major if a hidden failure is not detected and corrected. In other words, the consequence of any hidden function failure is increased exposure to the consequences of a multiple failure.

Corrosion Failure Examples As mentioned in Chapter 1, corrosion failures are very environmentally context specific. As it is becoming obvious here, corrosion failures are also very consequentially context specific. As another example, in the development of a burial site for storing radioactive waste a corrosion failure would occur if a minimum amount of radioactivity would leach in the groundwater after somewhere in the range of 10 to 1 million years.

Thus, the overall concept of failure in this context may have nothing to do with the integrity of the storage container, but everything to do with the transport of radioactive species in the surrounding environment.

This particular problem is challenging since it is not so easy to monitor the performance of containers of the radioactive waste owing to the long times and their relative inaccessibility associated with radioactivity 3. The F fighter aircraft crashes mentioned earlier in this chapter and the Aloha incident described in Chapter 1 are good examples of documented corrosion related failures.

In addition to these, the following recent failures have been selected for their importance and consequences. Note at the onset that all these 2. Defects And Failures 35 accidents could have been prevented if proper maintenance and inspection had been carried out. Bhopal Accident Bhopal is probably the site of the greatest industrial disaster in history. Between and , Union Carbide India Limited, located within a crowded working class neighborhood in Bhopal, was licensed by the Madhya Pradesh Government to manufacture phosgene, monomethylamine, methylisocyanate, and the pesticide carbaryl, also known as Sevin.

The addition of water to the tank caused a runaway chemical reaction, resulting in a rapid rise in pressure and temperature. The heat generated by the reaction, the presence of higher than normal concentrations of chloroform, and the presence of an iron catalyst, produced by the corrosion of the stainless steel tank wall, resulted in a reaction of such momentum that gases formed could not be contained by safety systems 4.

Consequently, methylisocyanate and other reaction products, in liquid and vapor form, escaped from the plant into the surrounding areas. There was no warning for people surrounding the plant since the emergency sirens had been switched off.

The effect on the people living in the shanty settlements just over the fence was immediate and devastating. Many died in their beds, others staggered from their homes, blinded and choking to die in the street.

It has been estimated that at least people died as a result of this accident, while figures for the number of people injured currently range from , to ,, with an estimated , typically quoted.

The processing plant was closed down after the accident. The Bhopal disaster was the result of a combination of legal, technological, organizational, and human errors.

The immediate cause of the chemical reaction was the seepage of L of water into the methylisocyanate storage tank. The results of this reaction were exacerbated by the failure of containment and safety measures and by a complete absence of community information and emergency procedures.

The long-term effects were made worse by the absence of systems to care for and compensate the victims. Furthermore, safety standards and maintenance procedures at the plant had been deteriorating and ignored for months. Carlsbad Pipeline Explosion At 5: The released gas ignited and burned for 55 min. Twelve persons who were camping under a concrete-decked steel bridge that supported the pipeline across the river were killed and their 36 Chapter 2 Corrosion Detectability three vehicles destroyed.

Investigators visually examined the pipeline that remained in the crater as well as the three 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 perforation was visible.

No significant corrosion damage was visible on the outside surfaces of the three pieces or on the two ends of the pipeline remaining in the crater. The drip between the closest block valve and the rupture site was removed from the pipeline and visually examined.

The drip was found to contain a blackish oily powdery grainy material. No significant material was observed in the area just underneath and several centimeters away from the siphon drain at the closed end of the drip.

No significant internal corrosion was observed in the drip. Interconnecting pits were observed on the inside of the pipe in the ruptured area. Typically, these pits showed the striations and undercutting features that are often associated with microbial corrosion.

A pit profile showed that chloride concentration in the pits increased steadily from top to bottom. Increased chloride concentration can result from certain types of microbial activity. This accident created a sense of urgency in the corrosion engineering community that NACE International took seriously by forming a special training task group.

The Internal Corrosion for pipelines course that resulted from this effort was soon followed by the production of a field guide to help inspectors recognize this serious problem 6.

Guadalajara Sewer Explosion The following corrosion failure was also due to a combination of human errors and shared responsibilities. The sewer explosion that killed people in Guadalajara, Mexico, in April , also caused a series of blasts that damaged buildings and injured people. At least nine separate explosions were 2. Defects And Failures 37 Fig. Courtesy of Dr. Jose M. Malo, Electric Research Institute, Mexico.

The trench was contiguous with the city sewer system, and the open holes at least 6 m deep and 3 m across. In several locations, much larger craters of 50 m in diameter were evident with numerous vehicles buried or toppled into them. The sewer explosion was traced to the installation of a water pipe by a contractor several years before the explosion that leaked water on a gasoline line lying underneath.

Corrosion Inspection and Monitoring

The cathodically protected gasoline pipeline had a hole within a cavity and an eroded area, all in a longitudinal direction. A second hole did not perforate the internal wall. The galvanized water pipe obviously had suffered stray current corrosion effects that were visible in pits of different sizes Fig. The subsequent corrosion of the gasoline pipeline, in turn, caused leakage of gasoline into a main sewer line. The Mexican attorney general sought negligent homicide charges against four officials of Pemex, the government-owned oil company.

The cause of the crash was attributed to the loss of the number 3 and 4 engines from the wing that in turn caused a complete loss of control of the airplane. The reason for the number 3 engine separation was a breakage of the fuse pin. The pin was designed to break when an engine seizes in flight, producing a large amount of torque.

Both of the engines were stripped off the right wing causing the Boeing Freighter to crash as it maneuvered toward the airport 8. A possible reason for the shearing away of the two right engines was that corrosion pits and fatigue weakened the fuse pins that hold the strut to the wings. Constant pressure variance coupled with corrosion is a terrible force that can cause corrosion pits to expand into cracks, such as the 4. It is believed that in the El Al crash the inboard fuse pin failed due to corrosion cracking and fatigue, which caused the outboard fuse pin, already weakened by a crack, to fail.

With these two pins malfunctioning the No. This design of the fuse pin has been used since and in a 7-year period there have been 15 reports of cracked pins. It was discovered that these pin failures resulted from the absence of primer, cadmium plating, and a corrosion prevention compound. Since the El Al crash, Boeing has also been trying to upgrade the The reactor vessel head is the dome-shaped upper portion of the carbon steel vessel housing the reactor core.

It can be removed when the plant is shut down to allow spent nuclear fuel to be replaced with fresh fuel. The CRDM nozzles connect motors mounted on a platform above the reactor vessel head to control rods within the reactor vessel. Operators withdraw control rods from the reactor core to startup the plant and insert them to shut down the reactor. The reactor core at the Davis—Besse nuclear plant sits within a metal pot designed to withstand pressures up to 17 MPa.

The reactor vessel has carbon steel walls nearly 15 cm thick to provide the necessary strength. Because the water cooling the reactor contains boric acid, which is highly corrosive to carbon steel, the entire inner surface of the reactor vessel is covered with 0. Because the outer surface lacked a protective stainless steel coating, boric acid ate its way through the carbon steel wall until it reached the backside of the inner liner. High pressure inside the reactor vessel pushed the stainless steel 2.

Defects And Failures 39 outward into the cavity formed by the boric acid. The stainless steel bent, but did not break. Cooling water remained inside the reactor vessel not because of thick carbon steel, but due to the thin stainless steel layer.

The corrosion incident also exposed problems within the staff of the regulatory commission, which initially wanted prompt inspections of all 68 plants that could be vulnerable to the problem, but relented and gave the owners permission to delay, leaving time for the hole in the lid to grow. Plants are designed with emergency equipment to cope with leaks, but the designs do not contemplate failure of the thick steel in that location.

The commission had a photo taken during a refueling shutdown in that showed evidence of the corrosion damage, but, according to the inspector general, officials failed to act on it.

One of the injured men later died, bringing the total to five fatalities. The rupture was in the condensate system, upstream of the feedwater pumps. The pipe wall at the rupture location had thinned from 10 to 1. Although the carbon steel pipe carried the high temperature steam at high pressure, it had not been inspected since the power plant opened in Four days before the scheduled shutdown and inspection, superheated steam blew the cm wide hole in the pipe.

The steam that escaped had not been in contact with the nuclear reactor, and no nuclear contamination has been reported. Already slowed by local opposition, this program was in danger of being stalled by the accident, the most deadly in the history of nuclear power in Japan.

Some 19, tons were spilled. This is equal to the total amount of oil spilled worldwide in The sunken bow section still contained tons of cargo and the stern had a further tons. The bow section sank within 24 h. The stern section sank on December 13 while under tow. The economic consequences of the incident have been felt across the region; a drop in the income from tourism, loss of income from fishing, and a ban on the trade of sea products, including oysters and crabs, have added to the discomfort of local populations.

Corrosion problems had been apparent on the Erika since at least , with details readily available to port state control authorities and potential charterers. In addition, there were numerous deficiencies in her firefighting and inert gas systems, pointing to a potential explosion risk on the tanker.

However, no immediate remedial action had been taken. According to publicly available, U. Her certificate of financial responsibility, a document legally required by tankers wishing to trade in U. It was also found that there were holes in both the portside and starboard inert gas system risers, which are critical items of safety equipment.

Malfunctions would tend to increase vulnerability to explosions. In an inspection in in New Orleans, the U. Coast Guard ordered that no cargo operations requiring the use of inert gas systems should be conducted until permanent repairs had been effected. Pinhole leaks remained in the firemain, contrary to Safety of Life at Sea convention regulations.

Another example of major losses to corrosion that could have been prevented and that was brought to public attention on numerous occasions since the s, is related to the design, construction, and operating practices of bulk carriers. In , while operating off the coast of Australia, the complete bow section became detached from the vessel. Miraculously, no lives were lost, there was little pollution, and the vessel was salvaged.

Throughout this period 2. Defects And Failures 41 it seems to have been common practice to neither use coatings nor cathodic protection inside ballast tanks. Not surprisingly therefore, evidence was produced that serious corrosion had greatly reduced the thickness of the plate and that this, combined with poor design to fatigue loading, were the primary cause of the failure. There have been many others involving large catastrophic failures, although in many of these cases there was little or no hard evidence on what actually caused the ships to go to the bottom.

This catastrophic explosion has been traced to the failure of a bypass assembly introduced into a train of six cyclohexane oxidation reactors after one of the reactors was removed owing to the development of a leak.

The leaking reactor, like the others, was constructed of One of the factors contributing to the crack was SCC, resulting from the presence of nitrates from the contaminated river water being used to cool a leaking flange. Swimming Pool Roof Collapse In , 12 people were killed in Uster, Switzerland when the concrete roof of a swimming pool collapsed after only 13 years of use.

The roof was supported by stainless steel rods in tension, which failed due to SCC. There have been other incidents associated with the use of stainless steel in safety critical load bearing applications in the environment created by modern indoor swimming pools and leisure centers.

The collapse of this ceiling above a swimming pool showed how a simple structural concept could be sensitive to the loss, through corrosion, of support from one of many hangers.

The steel rods had been pitted, causing the roof to cave in. The roof collapsed in a zipper-like fashion, starting with the corroded rods. The collapse continued as the remaining rods were unable to bear the increased load.

The chloride was either already present in the concrete or came from the pool via water vapor. Chloride can overcome the passivity of the natural oxide film on the surface of the steel. The inspection of safety-critical stainless steel components for SCC and loss of section by pitting should be viewed as a priority. The following inspection procedures have since that accident been recommended: Although not definitive, a normal telltale sign is brown staining, varying from a pale, dry discoloration to wet pustules.

Where tests reveal the presence of SCC a full risk assessment of the affected components should be carried out by qualified personnel. Age-Reliability Characteristics The failure patterns of complex systems have been extensively studied to improve maintenance strategies and operational procedures.

Six basic patterns shown in Fig. Pattern A is often referred to in reliability literature as the bathtub curve. This type of curve has three identifiable regions: An infant-mortality region, the period immediately after manufacture or overhaul in which there is a relatively high probability of failure. A region of constant and relatively low failure probability. A wearout region, in which the probability of failure begins to increase rapidly with age.

Pattern B is characterized by a constant or gradually increasing failure probability, followed by a pronounced wearout region. Once again, an age limit may be desirable.

Pattern C shows a gradually increasing failure probability, but with no identifiable wearout age. It is usually not desirable to impose an age limit in such cases. Pattern D starts with a low failure probability when the item is new or just out of the shop, followed by a quick increase to a constant level. Pattern E, which is characterized by a constant probability of failure at all ages. Defects And Failures 43 a b c d e Fig. Six patterns of f failure 2.

Pattern F in which infant mortality is followed by a constant or very slowly increasing failure probability. This behavior is particularly applicable to electronic equipment. In the s United Airlines carried out a systematic study of component failures to reveal their failure patterns.

In this study, it was found that the relative frequency of each type of conditional-probability curve proved especially interesting.

In fact, after a certain age the conditional probability of failure continued on at a constant rate curves D, F. However, it is obvious that if the failure pattern of a system has a wearout behavior, that is, curves A and B, it would be justified to recommend that a corrective action be taken before this system enters the wearout zone in order to reduce the overall failure rate.

In such cases, allowing the system to age well into the wearout region would cause an appreciable increase in the failure rate. While the presence of a well-defined wearout region exists in only two of the six curves in Fig.

Since corrosion is definitively an aging process, its influence typically follows pattern B in Fig. Probability of Failure To determine the probability of a failure POF , two fundamental issues must be considered: What are the specific forms of corrosion and their rates?

What is the possible effectiveness of corrosion inspection or monitoring? The input of corrosion experts is required to identify the relevant forms of corrosion in a given situation and to determine the key variables affecting the propagation rate. It is also important to realize that full consensus and supporting data on the variables involved is highly unlikely in real-life complex systems and that simplification will often be necessary.

One semiquantitative approach for ranking process equipment is based on internal POF. The procedure requires a fair degree of engineering judgment and experience and, as such, is dependent on the background and expertise of the analyst.

The POF approach is based on a set of rules heavily dependent on detailed inspection histories, knowledge of corrosion processes, and knowledge of normal and upset conditions. The equipment rankings may have to be changed and could require updating as additional knowledge is gained, process conditions change, and equipment ages. Maximum benefits of the procedure depend on fixed equipment inspection programs that permit the capture, documentation, and retrieval of inspection, maintenance, and corrosion—failure mechanism information.

The POD concept and methodology have since then gained widespread acceptance and continuing improvements have enhanced its acceptance as a useful metric for quantifying and assessing nondestructive evaluation NDE capabilities.

Forms of Corrosion 45 2. The actual importance of each corrosion type will also differ between systems, environments, and other operational variables. However, there are surprising similarities in the corrosion failure distributions within the same industries as can be seen by comparing Fig. Both corrosion failure distribution charts represent data for two large chemical plants, but they are from two different continents.

These corrosion failure statistics are for a chemical plant located in Germany Fig. This surprising similarity indicates that corrosion problems are very similar worldwide in the chemical industry and thus, ways to prevent these corrosion service failures should be similar The multifaceted nature of corrosion damage has long been recognized.

The classification that seems to have gained the widest acceptance was first presented Group I: Main forms of corrosion attack regrouped by their ease of recognition Failure statistics of large chemical process plant in Germany a , and in the United States b. The forms of corrosion shown in Fig. Those recognizable with the unaided eye. Those that are more easily discerned with specific aids e. Forms of Corrosion 47 3. Those that can only be identified definitely by optical or electronic microscopy.

These types of corrosion could also be organized on the basis of other factors e. The degree of localization refers to the selective attack by corrosion at small special areas or zones on a metal surface in contact with an environment. It usually occurs under conditions where the largest part of the exposed surface is either not attacked or is attacked to a much smaller degree than at local sites.

The degree of localization is an important aspect of any type of corrosion for many reasons. One reason is that the degree of corrosion severity usually increases with the degree of localization, often leading to a more serious problem, such as stress corrosion cracking SCC. Another reason is that the detectability of a corrosion defect decreases with its degree of localization.

The most common type of localized corrosion is pitting, in which small volumes of metal are removed by corrosion from certain areas on the surface to produce craters or pits. Pitting corrosion may occur on a metal surface in a stagnant or slow moving liquid. It also may be caused by crevice corrosion, poultice corrosion, deposition corrosion, cavitation, impingement, and fretting corrosion.

Among the metallurgical features of importance, the grain structure of a metallic material is probably the most determining in relation to corrosion damage.

A common type of corrosion attack for which the grain structure is important is intergranular or intercrystalline corrosion, during which a small volume of metal is preferentially removed along paths that follow the grain boundaries to produce what might appear to be fissures or cracks.

The same kind of subsurface fissures can be produced by transgranular or transcrystalline corrosion. In this, a small volume of metal is removed in preferential paths that proceed across or through the grains. Intergranular and transgranular corrosion sometimes are accelerated by tensile stress. In extreme cases, the cracks proceed entirely through the metal, causing rupture or perforation. This condition is known as SCC.

In a completely different type of corrosion, which is highly dependent on the metallurgical make-up, one of the metals in an alloy may be selectively leached out without producing visible pits or cracks and without changing the dimensions of the metal. At a casual glance, the metal may appear to be intact. Under a microscope, however, it can be seen to be porous.

The mechanical properties of the alloy are greatly reduced by the selective attack. The most common example of this type is dezincification of brass in which the zinc is selectively dissolved out of the alloy. While the types of corrosion identified in Fig. The unfolding of a 48 Chapter 2 Corrosion Detectability crevice situation, for example, will typically create an environment favorable for pitting, intergranular attack and even cracking.

Uniform Attack General corrosion is usually the least threatening type of attack, allowing one to forecast with some accuracy the probable life of equipment. Except in rare cases of a grossly improper choice of material for a particular service, or an unanticipated drastic change in the corrosive nature of the environment or complete misunderstanding of its nature, failures of metals by rapid general attack wasting away are not often encountered.

From a corrosion inspection point of view, uniform attack is relatively detectable and its effects predictable, hence it may be less troublesome than other forms of corrosion unless the corroding material is hidden from sight. The internal corrosion of pipeline and that of any other buried or immerged structures or the corrosion of hidden components are good examples that even the simplest corrosion process needs to be monitored.