Corrosion Guide

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Faqeer, Saudi Aramco. We're sorry, something went wrong. We are unable to complete this action. Please try again at a later time. Use this error code for reference:. You have previously purchased this item. Remaining Credits. Please review your transaction. An ex- ample is shown in Fig. Biological corrosion results from a reaction between the pipe material and organisms such as bacteria, algae, and fungi.

It is an important factor in the taste and odor problems that develop in a system, as well as in the degradation of the piping materials. Controlling such growths is compli- cated because they can take refuge in many protected areas, such as in mechanical crevices or in accumulations of corrosion products. The bacteria can exist under tubercles, where neither chlorine nor oxygen can destroy them.

Mechanical cleaning may be necessary in some systems before control can be accomplished by residual disinfectants. Preventative methods include avoiding dead ends and stagnant water in the system. Other types of corrosion in the waterworks industry that are not found as commonly as those discussed previously include 1 stray current corrosion and 2 dealloying or selective leaching.

Stray current corrosion is a type of localized corrosion usually caused by the grounding of home appliances or electrical circuits to the water pipes. Corrosion takes place at the anode, the point where the current leaves the metal to return to the power source or to ground.

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Stray current corro- sion is difficult to diagnose since the point of corrosion does not necessarily occur near the current source. It occurs more often on the outside of pipes, but does show up in house faucets or other valves. Dealloying or selective leaching is the preferential removal of one or more metals from an alloy in a corrosive medium, such as the removal of zinc from brass dezincification. This type of corro- sion weakens the metals and can lead to pipe failure in severe cases.

An exam- ple of this is shown in Fig. Pitting of steel pipe. Tuberculation in a cast iron pipe. Galvanized steel pipe from a domestic hot-water system showing almost complete clog- ging by corrosion products. Extreme example of stray current corrosion in an outside water faucet caused by lightning leaving the pipe. The purpose of this and the following sections is to point out some of the easiest, as well as the most effective, methods of identifying, monitoring, and correcting corrosion-related problems.

In other words, these sections answer the questions how do you know if your utility has a corrosion problem, and what can you do to control or reduce the effects of the corrosion. The effects of corrosion, which may not be evident without monitoring, can be expensive and may even affect human health. Monitoring methods most useful to the small water utility are emphasized; that is, those methods which are the least expensive and the simplest to implement in terms of manpower and technical requirements.

Methods for control- ling or reducing corrosion are covered in the following section. Just as there is no one cause of corrosion, there is no one way to measure or "cure" corrosion. Since corrosion in a system depends on a specific water and the reaction of that water with specific pipe materials, each utility is faced with a unique set of problems. There are, however, general1 methods of measuring and monitoring for corrosion that can provide a basis for a sound corrosion control program for any utility.

Although no one method may provide an absolute or quantitative measure of corrosivity, several methods used together over a period of time will indicate if corrosion is occurring and will point out any undesirable effects on the system. The indirect methods do not measure corrosion rates. Rather, the data obtained from these methods must be compared and interpreted to determine trends or changes in the system. The indirect methods dis- cussed here are 1 customer complaint logs, 2 corrosion indices, and 3 water sampling and chemical analyses.

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The direct corrosion measurements call for the actual examination of a corroded surface or the measurement of corrosion rates, particularly actual metal loss. The direct methods discussed here are 1 examination of pipe sections and 2 rate measurements. The most common symptoms are listed in Table 6. The Table 6. For example, red water may also be caused by iron in the raw water that is not removed in treatment.

Therefore, in some cases, further investigation is necessary before attributing the complaint to corrosion in the system. Complaints can be a valuable corrosion monitoring tool if records of the complaints are organ- ized. The complaint record should include the customer's name and address, date the complaint was made, and nature of the complaint. The following information should also be recorded: 1.

Type of material copper, galvanized iron, plastic, etc. Whether the customer uses home treatment devices prior to consumption softening, carbon filters, etc. Whether the complaint is related to the hot water system and, if so, what type of material is used in the hot water tank and its associated appurtenances; and 4. Any follow-up action taken by the utility or customer.

These records can be used to monitor changes in water quality due to system or treatment changes. The development of a complaint map is useful in pinpointing problem areas. The complaint map would be most useful when combined with the materials map discussed in Sect. If complaints are recorded on the same map, the utility can determine if there is a relationship between complaints and the materials used.

To supplement the customer complaint records, it might be useful to send questionnaires to a random sampling of customers. These questionnaires should be short but thor- ough. A sample questionnaire used by the city of Seattle is shown in Fig. Customer complaint records and questionnaires are useful monitoring tools that can be used as part of any corrosion monitoring and control program.

The low costs associated with keeping a good record of complaints can be well worth the time. The resulting information would indicate the real effect of water quality at the customer's tap and would show the effect of any process changes made as part of a corrosion control program. Corrosion Indices Many attempts have been made to develop an index that would predict whether or not a water is corrosive; unfortunately, none of these attempts has been entirely successful.

However, several of Do you ever have rusty water? Yes If so, how often? Yes No Where? L Sample questionnaire. These indices can be calculated by all small utili- ties and can be used in an overall corrosion control program. Since the LSI and AI are the two most commonly used corrosion indices in the waterworks industry, they are the only indices discussed in detail in the following paragraphs.

However, several of the less frequently used indices are briefly described to acquaint the reader with their usefulness and method of calculation. A thin layer of CaCO3 is desirable, as it keeps the water from contacting the pipe and reduces the chance of corrosion. Although the pipe is protected from corrosion, excessive scaling can result in loss of carrying capacity in the system, as is shown in Fig. If the reaction proceeds to the left, the scale is dissolved, leaving the surfaces that had been protected exposed to corrosion.

Langelier Saturation Index. The LSI is the most widely used and misused index in the water treatment and distribution field. At pHs, a protective scale will neither be deposited nor dissolved. The LSI is defined by the following equation:. Excessive CaCOj scaling resulting in loss of carrying capacity. Values for A and B are tabulated in Tables 6. The log of the calcium and alkalinity is obtained from Table 6. Now, let's take as an example Chicago's tap water, which has the following characteristics: Calcium as CaCO3 , The step-by-step calculation of the LSI, using Tables 6. Source: Federal Register, Table 6.

The above examples show two important factors. First, they show the effect of the change in temperature and pH on the calculated LSI value. This demonstrates the need for accurate, onsite pH and temperature measurements. There are several limitations to the LSI. First, it is generally agreed that the LSI may only be used to estimate corrosive tendencies of waters within a pH range of 6. More importantly, the LSI only indicates the tendency for corrosion to occur. It is not a measurement of corrosivity. Pipe sections were physically examined to establish whether or not the water was corrosive.

The results confirm that the LSI, by itself, does not indicate corrosiveness. It is, however, a valuable monitoring tool where a protective CaCO3 film is being used or when used in conjunction with other indirect or direct corrosion monitoring methods. A useful procedure for estimating the pHs is an experimental method commonly called the Mar- ble Test. In this test, duplicate samples of the water are collected.

After a time interval usually 1 h or longer , aliquots from both samples are filtered and analyzed for alkalinity or pH. If the alkalinity or pH in the untreated sam- ple is greater than that of the sample with CaCO3, the water is supersaturated with CaCO3 and may be scale forming.

If the alkalinities or pHs of the two samples are equal, the water is just saturated with CaCO3. Aggressive Index AI. The AI was developed at the request of consulting engineers to govern the selection of the proper type I or II A-C pipe and to ensure long-term structural integrity. However, it can be a useful tool in select- ing materials or treatment options for corrosion control. A sample calculation for the AI follows.

Other corrosion indices commonly seen in the literature are 1. This curve is shown in Fig. The values obtained apply to the soft waters of the eastern seaboard of the United States, but not to the harder waters of the middle part of the country. The major contribution of this index is that it introduces factors other than CaCO3 solubility, such as dissolved oxygen, chloride ion, and noncarbonate hardness, as well as the useful effect of silica.

It can be useful in estimating the amount of precipitate that may be formed. There have been attempts to use other water quality parameters to predict the tendency of a water to attack metal pipes. The classic studies of the Illinois State Water Survey by Larson, Sollo, and their co-workers have shown that other factors, such as the ratios of various anions, velocity, pH, and calcium ion concentration, affect the rates of corrosion of mild steel and cast iron.

It was shown that increasing the Cl" to HCOs" ratio, particularly above 0. Graphic representation of the various degrees of corrosion and encrustation. These stu- dies have led to a much better understanding of corrosion but have not resulted in a corrosion index. Sampling and Chemical Analysis Since corrosion is affected by the chemical composition of a water, sampling and chemical anal- ysis of the water can provide valuable corrosion-related information. Some waters tend to be more aggressive or corrosive than others because of the quality of the water.

It is generally desirable to collect water samples at the following locations within the system: 1. Water entering the distribution system i.

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Water at various locations in the distribution system prior to household service lines, 3. Water in several household service lines throughout the system, and 4. Water at the customer's taps. Water entering the distribution system at the plant can be conveniently sampled from the clearwell, the storage tank, or a sample tap on a pipe before or after the high-service pump.

To represent conditions at the customer's tap, "standing" samples should be taken from an inte- rior faucet in which the water has remained for several hours i. The sample should be collected as soon as the tap is opened. A representative sample from the household service line between the distribution system and the house itself can be obtained by collecting a "running" sample from the customer's faucet after letting the tap run for a few minutes to flush the household lines.

Frequently, the water tempera- ture noticeably decreases when water in the service line reaches the tap. By letting the same faucet run for several minutes following the initial temperature change, the running water sample at the tap is representative of the water recently in the distribution main itself. If a comparison of the sampling results shows a change in the water quality, corrosion may be occurring between the sampling locations. Analysis of Corrosion By-product Material. Valuable information about probable corrosion causes can be found by chemically analyzing the corrosion by-product material.

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Scraping off a por- tion of the corrosion by-products, dissolving the material in acid, and qualitatively analyzing the solution for the presence of suspected metals or compounds can indicate the type or cause of corro- sion. These analyses are relatively quick and inexpensive. If a utility does not have its own labora- tory, samples of the pipe sections can be sent to an outside laboratory for analysis. The numerical results of these analyses cannot be quantitatively related to the amount of corrosion occurring since only a portion of the pipe is being analyzed.

However, such analyses can give the utility a good' overview of the type of corrosion that is taking place. The compounds for which the samples should be analyzed depend on the type of pipe material in the system and the appearance of the corrosion products. For example, brown or reddish-brown scales should be analyzed for iron and for trace amounts of copper. Greenish mineral deposits should be analyzed for copper. Black scales should be analyzed for iron and copper. Sampling Technique. Since many important decisions are likely to be made based on the sam- pling and chemical analyses performed by a utility, it is important that care be taken during the sampling and analysis to obtain the best data.

Samples should be collected without adding air, as air tends to remove CO2 and also affects the oxygen content in the sample. To collect a sample without additional air, fill the same container to the top so that a meniscus is formed at the opening and no bubbles are present. The sample bottle should be filled below the surface of the water. To do this, slowly run water down the side of a larger container and immerse the sample bottle in the larger container. Cap the sample bottle as soon as possible.

Recommended Analyses for Additional Corrosion Monitoring. The parameters which should be analyzed for in a thorough corrosion monitoring program depend to a large extent on the materials present in the system's distribution, service, and household plumbing lines. In all cases, temperature and pH should be measured in situ in the field. Dissolved gases, such as hydrogen sulfide H2S , oxygen, CO2, and chlorine residual, also should be measured as part of a corrosion monitoring pro- gram. These parameters can be measured in situ or fixed for laboratory measurement.

Total hard- ness, calcium, alkalinity, and TDS or conductivity must be measured if a protective coating of CaCO3 is used for corrosion control or if cement-lined or A-C pipe is present in the system. These analyses are also necessary to calculate the CaCO3-based corrosion indices. Measurement of anions, such as chloride and sulfate, may also indicate corrosion poten- tial. Frequency of analysis depends on the extent of the corrosion problems experienced in the sys- tem, the degree of variability in raw and finished water quality, the type of treatment and corrosion control practiced by the water utility and cost considerations.

Interpretation of Sampling and Analysis Data. Comparing sampling data from various locations within the distribution system can isolate sections of pipe that may be corroding. Increases in levels of metals such as iron or zinc, for instance, indicate potential corrosion occurring in sections of iron and galvanized iron pipe, respectively.

The presence of cadmium, a minute contaminant in the zinc alloy used for galvanized pipe, also indicates the probable corrosion of a galvanized iron pipe. Corrosion of cement-lined or A-C pipe is generally accompanied by an increase in both pH and calcium throughout the system, sometimes in conjunction with an elevated asbestos fiber count. The following example illustrates the changes that can take place between a distribution system and a customer's tap. The analytical results in Table 6. In this case, A-C pipe is used throughout the distribution system.

The home plumbing systems are mostly copper. The water in the distribution system had no traces of copper or lead, and the LSI, calculated from the data as the water entered the distribution system, was slightly positive or potentially non- corrosive. Data in Table 6. Further investigation of the household plumbing showed that the customer's hot water system was corroding.

Another example of the importance of data interpretation to an overall corrosion monitoring program is discussed below for A-C pipe. Recommended analyses for a thorough corrosion monitoring program In situ measurements pH, temperature Dissolved gases Oxygen, hydrogen sulfide, carbon dioxide, free chlorine Parameters required to calculate CaCOa-based Calcium, total hardness, alkalinity, total dis- indices, or required for cement-lined or solved solids, fiber count A-C pipe only A-C pipe Heavy Metals Iron or steel pipe Iron Lead pipe or lead-based solder Lead Copper pipe Copper, lead Galvanized iron pipe Zinc, iron, cadmium, lead Anions Chloride, sulfate Source: Environmental Science and Engineering, Inc.

Water quality data from a Florida water utility 0 , , ,. Cu Pb Samp e ocation , ,, , , ,. The following conditions indicate situations in which the water may not attack A-C pipe; 1. An initial AI above about 11; 2. No significant change in the pH or the concentration of calcium at different locations in the system; 3.

No asbestos fibers consistently found in representative water samples after passage through A- C pipe; a. Significant asbestos fiber counts being found in representative water samples at one time but not another at a location where water flow is sufficient to clean the pipe of tapping debris recent tapping can cause high fiber counts not related to pipe attack and b.

Significant asbestos fiber counts being found only in water samples collected from low- flow dead ends or from fire hydrants nonrepresentative samples and nowhere else in the system. The following conditions indicate situations in which the water may be attacking A-C pipe: 1. An initial AI below about 11, 2. A significant increase in pH and the concentration of calcium at different locations in the sys- tem, 3. Significant asbestos fiber counts being found consistently in representative water samples col- lected from locations where a the flow is sufficient to clean the pipe of debris and b the pipe has been neither drilled nor tapped near or during the sampling period, and 4, Inlet water screens at coin-operated laundries become plugged with fibers.

The data obtained by sampling for corrosive characteristics can be used as a guide to water quality changes that might be required to reduce or control corrosion, such as pH adjustment or the addition of silicates or phosphates. Results of additional sampling, conducted after starting a corro- sion control program, can indicate the success of any water quality changes.

For example, a high concentration of calcium in a scale may shield the pipe wall from DO diffusion and thereby reduce the corrosion rate. Methods used to examine scale on pipe walls include physical inspection [both macroscopic human eye and microscopic], X-ray diffraction, and Raman spcctroscopy. Physical inspection is the only method of practical use to utility personnel, as X-ray diffraction and Raman spectroscopy require expensive, complicated instruments and experienced personnel to interpret the results.

Physical Inspection. Physical inspection is usually the most useful inspection tool to a utility because of the low cost. Both macroscopic human eye and microscopic observations of scale on the inside of the pipe are valuable tools in diagnosing the type and extent of corrosion. Macroscopic studies can be used to determine the amount of tuberculation and pitting and the number of crev- ices. The sample should be examined also for the presence of foreign materials and for corrosion at joints. Utility personnel should try to obtain pipe sections from the distribution or customer plumbing systems whenever possible, such as when old lines and equipment are replaced.

If a scale is not found in the pipe, an examination of the pipe wall can yield valuable information about the type and extent of corrosion and corrosion-product formation, such as tubercles , though it may not indicate the most probable cause. Examination under a microscope can yield even more information, such as hairline cracks and local corrosion too small to be seen by the unaided eye. Such an examination may provide addi- tional clues to the underlying cause of corrosion by relating the type of corrosion to the metallurgi- cal structure of the pipe. Photographs of specimens should be taken for comparison with future visual examinations.

High magnification photographs should be taken, if possible. X-ray Diffraction. The diffraction patterns of X-rays of scale material can be used to identify scale constituents. The diffraction of the X-rays will produce a pattern on a film strip which can be compared with X-ray diffraction patterns of known materials. It is possible to identify complex chemical structures by their X-ray "fingerprint. Raman spectroscopy is a technique for identifying compounds present in corrosion scale and films without removing a metal sample.

In Raman spectroscopy, an infrared beam is reflected off the surface to be analyzed, and the change in frequency of the beam is recorded as the Raman spectrum. This spectrum, which is different for all compounds, is compared with Raman spectra of known materials to identify the constituents of the corrosion film. Raman spectroscopy and X-ray diffraction are useful in corrosion research and in corrosion stu- dies where the nature of the scale is unknown.

However, the cost of the analyses makes them too expensive to be used in solving most corrosion problems. Nearly all corrosion problems can be solved without the detailed information provided by these techniques. Rate Measremcnts Rate measurements are another method frequently used to identify and monitor corrosion.

The corrosion rate of a material is commonly expressed in mils 0. Common methods used to measure corrosion rates include 1 weight-loss methods coupon testing and loop studies and 2 electrochemical methods. Weight-loss methods measure corrosion over a period of time. Electrochemical methods measure either instantaneous corrosion rates or rates over a period of time, depending on the method used.

Coupon Weight-Loss Method. This method uses "coupons" or pipe sections as test specimens. It is used for field, pilot-, and bench-scale studies, provided the samples are cleaned and installed in the corrosive environment in such a way that the attack is not influenced by the pipe or container. The coupons usually are placed in the middle of the pipe section. The weight of the specimen or coupon is measured on an analytical balance before and after immersion in the test water. Coupon weight-loss test results do not measure localized corrosion but are an excellent method for measuring general or uniform corrosion.

Coupons are most useful when corrosion rates are high so that weight loss data can be obtained in a reasonable time. The ASTM method above should be followed. Following are lists of the advantages and disadvantages of the coupon method: Advantages 1. Disadvantages 1.

Loop System Weight-Loss Method. Another method for determining water quality effects on materials in the distribution system is the use of a pipe loop or sections of pipe. Either the loop or sections can be used to measure the extent of corrosion and the effect of corrosion control methods. Pipe loop sections can be used also to determine the effects of different water qualities on a specific pipe material.

The advantage is that actual pipe is used as the corrosion specimen. The loop may be made from long or short sections of pipe. Water flow through the loop may be either continuous or shut off with a timer part of the time to duplicate the flow pattern of a household. Pipe sections can be removed for weight-loss measure- ments and then opened for visual examination. Following are lists of the advantages and disadvantages of a loop system; Advantages 1. Electrochemical Rate Measurements. These methods are based on the electrochemical nature of corrosion of metals in water.

An increasing number of these instruments are now on the market. However, they are relatively expensive and probably not widely used by smaller utilities. They are discussed here for completeness. One type of electrochemical rate instrument has probes with two or three metal electrodes that are connected to an instrument meter to read corrosion in mpy. The electrode materials can be made of the material to be studied and inserted into the pipe or corrosive environment. For the other type, the loss of material over time is detected by an increase in the resistance of an electrode made of the metal of interest.

Measurements made over a period of time can be used to estimate corrosion rates. Following are lists of the advantages and disadvantages of electrical resistance measurements: Advantages 1. A schematic representation of a general approach to solving corrosion problems is shown in Fig, 7. To completely eliminate corrosion is difficult if not impossible. There are, however, several ways to reduce or inhibit corrosion that are within the capability of most water utilities.

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This sec- tion describes several methods most commonly used to control corrosion. The utility operator should use common sense in selecting the best and most economical method for successful corrosion control in a particular system. Because corrosion depends on both the specific water quality and pipe mate- rial in a system, a particular method may be successful in one system and not in another. Corrosion is caused by a reaction between the pipe material and the water in direct contact with each other. Consequently, there are three basic approaches to corrosion control: 1, modify the water quality so that it is less corrosive to the pipe material, 2.

The most common ways of achieving corrosion control are to 1. As discussed in Sect. In general, the less reactive the material is with its environ- ment, the more resistant the material is to corrosion. When selecting materials for replacing old lines or putting new lines in service, the utility should select a material that will not corrode in the water it contacts.

Admittedly, this provides a limited solution since few utilities can select materials based on corrosion resistance alone. Usually several alternative materials must be compared and evaluated based on cost, availability, use, ease of installation, and maintenance, as well as resistance to corrosion. In addition, the utility owner may not have control over the selection and installation of the materials for household plumbing. There are, however, several guidelines that can be used in selecting materials.

First, some materials are known to be more corrosion resistant than others in a given environ- ment. For, example, a low pH water that contains high DO levels will cause more corrosion damage in a copper pipe than in a concrete or cement-lined cast iron pipe. Other guidelines relating water quality to material selection are given in Table 4. Second, compatible materials should be used throughout the system.

Two metal pipes having different activities, such as copper and galvanized iron, that come in direct contact with others can set up a galvanic cell and cause corrosion. The causes and mechanisms of galvanic corrosion are discussed in Sect. As much as possible, systems should be designed to use the same metal throughout or to use metals having a similar position in" the galvanic series Table 3.

Galvanic corrosion can be avoided by placing dielectric insulating couplings between dissimilar metals. Steps toward solving corrosion problems. A faulty design may cause severe corrosion, even in materials that may be highly corrosion resistant. Some of the important design considerations include 1. Many plumbing codes are outdated and allow undesirable situations to exist.

Such codes may even create problems, for example, by requiring lead joints in some piping. Where such problems exist, it may be helpful for the utility to work with the responsible government agency to modify outdated codes. Because of the differences among raw water sources, the effec- tiveness of any water quality modification technique will vary widely from one water source to another.

However, where applicable, water quality modification can often result in an economical method of corrosion control. Acid waters are generally corrosive because of their high concentration of hydrogen ions. When corrosion takes place below pH 6. In the range between pH 6. Most materials used in water distribution systems copper, zinc, iron, lead, and cement dissolve more readily at a lower pH. Increasing the pH increases the hydroxide ion OH" concentration, which, in turn, decreases the solubility of metals that have insoluble hydroxides, including copper, zinc, iron, and lead.

When carbonate alkalinity is present, increasing the pH, up to a point, increases the amount of carbonate ion in solution. The cement matrix of A-C pipe or cement-lined pipe is also more soluble at a low pH. Increasing the pH is a major factor in limiting the disso- lution of the cement binder and thus controlling corrosion in these types of pipes, 3.

The relationship between pH and other water quality parameters, such as alkalinity, carbon dioxide CO2 , and TDS, governs the solubility of calcium carbonate CaCO3 , which is com- monly used to provide a protective scale on interior pipe surfaces. To deposit this protective scale, the pH of the water must be slightly above the pH of saturation for CaCO3, provided sufficient alkalinity and calcium are present.

A protective coating of CaCO3, for instance, will not form unless a sufficient number of carbonate and calcium ions are in the water. Some metals, notably lead and copper, form a layer of insoluble carbonate, which minimizes corrosion rates and the dissolution of these metals. In low alkalinity waters, carbonate ion must be added to form these insoluble carbonates. The number of carbonate ions available is a complex function of pH, temperature, and other water quality parameters.

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Bicarbonate alkalinity can be converted to carbonate alkalinity by increasing the pH. If carbonate supplementing is neces- sary to control corrosion in a water system, pH also must be carefully adjusted to ensure that the desired result is obtained. The proper pH for any given water distribution system is so specific to its water quality and sys- tem materials that a manual of this type can provide only general guidance.

Other indices can be used to check this value. To start, the pH of the water should be adjusted such that the LSI is slightly positive, no more than 0. Keeping the pH above the pHs should cause a protective coating to develop. If no coating forms, then the pH should be increased another 0. It is important to watch the pressure in the system carefully as too much scale build-up near the plant could seriously clog the transmission lines. Soft, low alkalinity waters cannot become supersaturated with CaCOj regardless of how high the pH is raised.

In fact, raising the pH to values greater than about Excess hydroxide alkalinity is of no value since it does not aid in CaCO3 precipitation. For systems that do not rely on CaCO3 deposition for corrosion control, it is more difficult to estimate the optimum pH. Practical minimum lead solubility occurs at a pH of about 8. Phosphates and other corrosion inhibitors often require a narrow pH range for maximum effec- tiveness.

If such an inhibitor is used, consideration must be given to adjusting the pH to within the recommended range. Schematics of typical chemical feed systems are shown in Fig. The pH should be adjusted after filtration since waters having higher pHs need larger doses of alum for optimum coagulation.

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It is recommended that a corrosion monitoring program, such as that described in Sect. Evaluating the performance of chemi- cal feed systems for pH adjustment is the key to an effective corrosion control program. Addition of lime, soda ash, or other chemicals for pH control can be evaluated by continuous readout pH recorders.