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When steam has performed its work in manufacturing processes, turbines, building heat, etc. it transfers heat and reverts back to a liquid phase called steam condensate. However, not all the energy used in producing steam is lost when condensate is formed.

As most condensate return is still relatively hot (130OF to 225OF) , it is very valuable as a source of feedwater.

There is a significant fuel savings related to the heat required to raise the temperature of makeup water at (50OF to 60OF) to equal that of the return condensate, not to mention the additional cost in pretreating (softening) the makeup, as well as basic water cost itself.

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Attack of condensate and steam lines

Causes of condensate corrosion.

• Dissimilar Metals • Dissolved gasses • On / off operation

Effects of condensate corrosion The effects of condensate corrosion are either leaks or pipe blockage. Threaded joints are most susceptible to leaks as the metal has been thinned and stressed as a result of thread cutting. Horizontal pipes are more susceptible to attack than vertical ones.

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Carbon Dioxide

The presence of carbon dioxide and oxygen in the condensate are a serious problem. The gasses enter the system from either from leaks or thermal decomposition of carbonates and bi-carbonates in the boiler water and the carry over from dissolved oxygen in the feed.

The heat and pressure of the boiler break down the alkalinity in the boiler water to form carbon dioxide gas CO2. Leaving the boiler with the steam it travels throughout the plant supply system. When the steam condenses, the carbon dioxide dissolves in it to form carbonic acid. This reaction is chemically expressed as:

H2O + CO2 = H2CO3

which is a weak acid and drops the pH of the condensate.

As you can see by the table 1 ppm of CO2 will reduce the pH below neutral.

Once the carbonic acid has formed it becomes aggressive to iron and copper in the condensate system. The corrosion reaction for iron is shown below:

2H2CO3 + Fe => Fe(HCO3)2 +H2

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The resulting Fe(HCO3)2 is soluble and as such is removed by the condensate leaving behind nothing to protect the metal surface. Carbonic acid reveals itself as a general loss of metal. This takes the form of thinning of the metal on the lower diameter of the pipe. A corrosion problem in the condensate system usually first shows up as thinning of the pipe at threaded fittings and the downstream side of steam traps where abrupt pressure changes are present.

Fe(HCO3)2 can react with oxygen to form iron oxides thus freeing the carbon dioxide for further attack. This acid depresses the condensates pH and causes corrosion to take place. This corrosion appears as grooving or gouging in the bottom of steam headers or condensate return lines. Most often it weakens pipe walls at threaded joints and the resultant metal loss can lead to large amounts of copper and/or iron being returned to the boiler to cause troublesome deposits.

Oxygen, as in the boiler system, can cause localized attack in the form of pitting when present in the condensate system. This type of corrosion can generally cause equipment to fail more quickly than the generalized corrosion caused by carbonic acid attack due to it concentrating in a small area. Oxygen can infiltrate the system from open condensate receivers, poor deaeration or leaky siphons.

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Dissimilar metals Where dissimilar metals are in contact with one another galvanic corrosion will occur forming deposits downstream of the corrosion site, this leads to restricted flows in feed lines economizers and other equipment. If the condensate becomes contaminated with metallic compounds as a result of corrosion in the condensate corrosion will occur. Failure of boiler tubes can result if this deposition takes place on heat transfer surfaces.

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On / off operation

Considered a process steam consumption operating under on/off conditions. During normal operation (on) presents a corrosion rate of 2 mpy and produces dissolved iron as corrosion result of 0.05 ppm.

If operation turns to off, steam is condenced, pressure drops, and oxygen enters to the system as to brake the void.

Corrosion rate increases extremelly, and when system turns again to on extremelly high iron return is noticed.

During the off operation the deterioration of the system is very fast.

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There are three main chemical programs to control corrosion in the condensate system, being

• neutralizing amines, • filming amines and • mixtures of neutralizing and filming amines.

NEUTRALIZING AMINES are high pH materials which neutralize the carbonic acid formed in condensate systems. By raising and controlling pH level in condensate from 7.5 to 9.0, neutralizing amines retard acid attack and greatly reduce the amount of corrosion products entering the boiler. The three primary neutralizing amines in use today are:

• Morpholine - a low distribution ratio product. • Diethyleminoethanal (DEAE) - a medium distribution ratio product. • Cyclohexylamine - a high distribution ratio product.

The distribution ratio is used to predict the amine concentration in the steam and condensate phases and impacts significantly regarding proper amine selection.

Distribution Ratio = Amine in Steam Phase / Amine in Condensate Phase

Neutralizing amines have low flashpoints and therefore can be fed directly to the feedwater or boiler water, or they can be fed directly into the steam header. The feed rate is based on the amount of alkalinity present in the feedwater. Neutralizing amines offer excellent protection against carbonic acid attack, but little protection against oxygen attack.

FILMING AMINES are various chemicals that lay down a vary thin protective barrier on the condensate piping protecting it against both oxygen and carbonic acid attack. The protective film barrier is not unlike the protection afforded an automobile by an application of car wax.

The protective film barrier is continuously being removed (a little at a time), requiring continuous feeding of the filming amine based on steam flow rather than feedwater alkalinity.

Care must be taken to start this program slowly with an initial feedrate of one fifth that of the final feedrate to prevent the removal of old corrosion products from the system and their subsequent return to the boiler. Additionally, the filming amine should be fed using an injection quill to the steam header to insure proper vaporization and distribution throughout the steam system.

The formation of gunk balls (Gunking) can occur due to overfeed, contaminants in the condensate or wide pH swings causing deposits to form in low flow areas like steam traps.

COMBINATION NEUTRALIZING AND FILMING AMINES

As its name implies, are the combination of neutralizing and filming amines and are a successful alternative to protect against both carbonic acid attack and oxygen attack.

It combines the elevated pH approach to neutralize carbonic acid in conjunction with the protective barrier film approach.

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The neutralizing amines, although they will elevate pH, main purpose is to provide better distribution of the filming amine throughout the condensate system which in turn helps to prevent gunking.

As with filming amines it is better to be fed directly to the steam header utilizing an injection quill.

SUMMARY. Clearly each program or approach has certain features and benefits as well as limitations.

Each different set of operating conditions will tend to dictate the appropriate treatment that is required. The expected steam pressure, temperature, system metallurgy and the plants systems pH level all play an important role in determining the most effective treatment program.

Clearly each program or approach has certain features and benefits as well as limitations. Each different set of operating conditions will tend to dictate the appropriate treatment that is required.

The expected steam pressure, temperature, system metallurgy and the plant systems pH level all play an important role in determining the most effective treatment program.

OUR COMPANY

Offers a full range of neutralizing amines, filming amines and mixtures, as cover any system needs.

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There are three main chemical programs to control corrosion in the condensate system, being

• neutralizing amines, • filming amines and • mixtures of neutralizing and filming amines.

The most common method of addressing carbonic acid attack is through the use of neutralizing amines. These chemicals, such as morpholine and cyclohexylamine neutralize the carbon acid, and increase the pH of the condensate. Corrosion of mixed metallurgy condensate systems is minimized when the pH is maintained between 8.8 and 9.2.

Due to high alkalinity in boiler feedwater elevating the pH to this level may not be economical. In this case the pH should be maintained at 8.3 or higher, or a filming amine applied. A filming amine, such as octyldecylamine, provides a non-wettable protective barrier against both carbonic acid and oxygen.

When utilizing a filming amine, the pH is usually maintained between 6.5 and 7.5, so a neutralizing amine may still be required. Additionally, filming amines can be difficult to apply and generate fouling of the system, particularly in systems where they have not been applied previously.

In order to minimize oxygen pitting one can utilize a filming amine as previously mentioned, or a volatile oxygen scavenger such as DEHA (diethylhydroxyamine.) In the author’s opinion utilizing DEHA provides cost attractive, but sometimes unstable or even unpredictable results as it scavenges oxygen and passivates the condensate system, making it less susceptible to corrosion.

But the final protection is related to the oxygen presence, which can vary extremelly, and is related to the presence of neutralizing amine, as long as the final reaction products are strong organic acids, like acetic acid, which can extremelly dangerous in the condensate low alkalinity system.

Depending on the treatment method chosen, condensate monitoring can vary. In all cases the following tests should be performed.

1. Soluble and insoluble iron levels. 2. pH levels at various points in your steam condensate system. It is extremely

important that pH measurements be made on cooled ("unflashed") samples. If the sample is taken hot, carbon dioxide will flash, which results in artificially high pH measurements.

3. Condensate corrosion coupons.

If a filming amine is utilized, the residual should be measured. The same is true if DEHA is used as an oxygen scavenger. In the latter case, a residual of 100 to 150 ppb is usually targeted. Note that this may take time (as much as 3 to 6 months) since much of the DEHA will be consumed passivating the system. These are some general guidelines.

Our Product line:

• Our neutralizing amines • Our filming amines

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A class of inhibitors known as neutralizing amines or volatile amines is generally used to prevent afterboiler corrosion caused by low pH They neutralize carbonic acid and raise condensate pH Ammonia is also usually grouped with this class of inhibitors because its method of afterboiler corrosion prevention is through carbonic acid neutralization and pH increase.

Morpholine and Cyclohexylamine are the most commonly used neutralizing amines; others include Diethylaminoethanol, aminomethylpropanol, and methoxypropylamine.

Amines differ in cost, consumption rate and vapor-liquid distribution ratio. The distribution ratio (ratio of the amine concentration in the steam to that in the condensate) is important because it determines the amount of material present as the first portion of the steam condenses

Combining amines of differing distribution ratios provides an effective method of controlling corrosion throughout the afterboiler section.

Water Services Ltd produces and distributes two neutralizing amine product lines :

• WSB SLA mixtures based on Morpholine • WSB DEA mixtures based on Diethylamino Ethanol

Cycloexylamine is included in all formulations, but there is not a product line based to it, because has a relatively high distribution ratio, travels farther in the steam and reaches areas beyond those in which steam first condenses.

This can actually result in concentration pockets of the neutral carbonate salt that may exceed the solubility limit and thus cause deposition and possible fouling of traps and lines. These deposits can include ammonium carbonate, Cyclohexylamine carbonate, and Morpholine carbonate

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Combining amines of differing distribution ratios provides an effective method of control

Because neutralizing inhibitors return to the boiler with the condensate, they can be recycled. This is an important consideration in their use because the only loss is through non-returned condensate, steam released to the atmosphere or consumed in plant processes, or through slight venting losses in the deaerating equipment.

In the deaerating equipment, the stripping action of steam decomposes the amine-carbonate and removes most of the carbon dioxide. Only a small portion of the amine is removed through the vent of the deaerator. The amount varies with the distribution ratio . Amines with the lowest distribution ratio, like WSB SLA 3110 and WSB SLA 3115 suffer the lowest loss in the deaerator.

The remaining amine returns to the boiler in the feed water, enters the steam, and continues the cycle.

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WSB SLA is a group of neutralizing products, based on Morpholine as the main neutralizing amine compound.

% Diethyl amino ethanol

% Cyclohexylamine

WSB SLA 3110

WSB SLA 3115

WSB SLA 3120

10

5

2

--

5

8

In any steam-condensate mixture, the ratio of neutralizer in the condensate to that in the steam is inversely proportional to the distribution ratio. Morpholine, therefore, has the greatest potential to condense in the first condensate formed, at which time it will neutralize any carbon dioxide dissolved in this same first condensate. It can, therefore, offer the greatest protection in relatively small systems, or in areas within a system where steam

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first condenses.

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% Morpholine % Cyclohexylamine WSB DEA 3000 5 5 WSB DEA 3010 2 8 WSB DEA 3005 7 3

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Filming Amines

Filming amines represent an effective and economical approach to condensate system corrosion control. Protection by filming amines is through the formation of an adherent, nonwettable organic film on metal surfaces preventing contact between the metal surface and corrosive condensate. The treatment level, typically 1-3 ppm of the pure amine, is not dependent on carbon dioxide or oxygen concentration.

The chemicals historically used for this pur. are high molecular weight amines or amine salts which contain straight carbon chains of 10 to 18 atoms and include the following:

octadecylamine - CH3(CH2)16CH2NH hexadecylamine - CH3(CH2)14CH2NH2 dioctadecylamine - (CH3(CH2)16CH2)2NH

The acetate salts of these amines, or the pure compound in combination with an emulsifier, are often used to ease preparation of feed solutions or dispersions.

The amines by themselves are not soluble in water and they are usually incompatible with other boiler water treatment chemicals, the exceptions being volatile oxygen scavengers as previously discussed. Amines are dispersed in condensate-quality water kept in a separate tank and fed to the system through separate chemical feed pumps and lines.

In more recent times, advances have been made in filming amine chemistries to improve their performance. One of the more common filmers of this type is ethoxylated soya amine. Its chemistry versus that of octadecylamine is shown below.

octadecylamine ethoxylated soya amine

Soya amine shows several advantages over octadecylamine in that it is more water soluble due to the double bond in its hydrocarbon chain. This will lead to less of a sludging tendency of the film. Additionally, the ethoxyl groups bound to the nitrogen portion of the molecule provide two

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additional sites for bonding to the metal surface of the afterboiler lines, yielding a more durable film.

The octadecylamine containing filmers, are distributed from Water Services Ltd under the name of WSB SFA (Food approved), while the ESA containing are distributed under the WSB ESA.

All formulations include mixture of neutralizing and filming amines.

• WSB SFA • WSB ESA

Octadecylamine has been the most widely applied amine of this type. The amine group is hydrophilic and attaches itself to the metal surface. The "tail" is hydrophobic and prevents the corrosive condensate from wetting the surface. The degree of protection improves with closer packing. Un-branched primary amines pack very closely, while branched secondary or tertiary amines, due to their lateral orientation, usually exhibit lower degrees of protection in laboratory studies. In practice, however, a number of additional factors become significant.

It should be noted, however, that of all the filming amines, only octadecylamine is acceptable by FDA regulations for use in operations where the steam comes in contact with food or food products.

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Soya amine shows several advantages over octadecylamine in that it is more water soluble due to the double bond in its hydrocarbon chain. This will lead to less of a sludging tendency of the film.

Additionally, the ethoxyl groups bound to the nitrogen portion of the molecule provide additional sites for bonding to the metal surface of the afterboiler lines, yielding a more durable film.

Hints

Because high velocities result in potential erosion of the film, a continuous feed is required to replenish the material on surfaces where it has been eroded. In addition, deposits destroy the protection afforded by such filming amines, and they do not protect well in areas where pitting has already occurred. The presence of dissolved solids degrades or precipitates traditional filming amines significantly and renders them ineffective in a condensate contaminated by carryover from the boiler or by leakage in the process (e.g., oil in refineries). In addition, use of filming amines should be avoided when organic contamination of the steam is common to prevent stripping of the amine film by solvent-type organics.

Ferric oxide also presents a potential problem because it can cause polymerization of the amine, the results of which, combined with degradation products formed in the condensate, can accelerate corrosion. Over-treatment, whether caused by overfeed, poor distribution, or high recycling with the returned condensate, aggravates these problems.

Because filming amines have an affinity for underlying metal, they may undercut iron oxide deposits causing rapid slough-off, often a deterrent to their use in older plants. Sloughed-off iron oxide deposits mix with the adsorbed amine, causing blockage of traps and valves in the condensate system and in the spray nozzles of the deaerator. Even a gradual increase of amine dosage is often ineffective because pH excursions can break down the films formed by such amines. Filming amines are most

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effectively used on uncorroded metal in systems where condensate return is not high. They are generally not recommended for use in systems with high condensate return, in which the degraded or polymerized amine that is returned can result in deposit formation.

Because filming amines are most effective when applied to uncorroded metal, their use is most desirable in newer systems. The problems created by applying them to previously corroded metal surfaces can be overcome by the accompanying use of volatile oxygen scavengers. By passivating the metal surface, the scavenger "prepares" it for the filming amine. Filming amine bonds to passivated magnetite surfaces are far more stable and effective than bonds to hematite.

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Why Treat Condensates ?

What causes corrosion in steam condensate systems? Carbon dioxide and oxygen cause most condensate system corrosion. Carbon dioxide, dissolved in condensed steam, forms corrosive carbonic acid. If oxygen is present with carbon dioxide, the corrosion rate is much higher and is likely to produce localized pitting. Ammonia, in combination with oxygen, attacks copper alloys. How is steam condensate corrosion prevented? The general approach involves removing oxygen from the feedwater mechanically and chemically and providing pretreatment of the make-up water to minimize potential carbon dioxide formation in the boiler. Chemical treatment reduces corrosion potential further. Volatile amines neutralize carbonic acid formed when carbon dioxide dissolves in condensate. Volatile filming inhibitors form a barrier between the metal and the corrosive condensate. How do chemical oxygen scavengers help control condensate system corrosion? Deaerators (and feedwater heaters) remove oxygen mechanically. The best-designed and operated deaerators can reduce oxygen to as low as 0.007 PPM. Since very small amounts of oxygen can cause corrosion, complete oxygen removal often requires chemical treatment.

What is the basis for choosing between neutralizing and filming inhibitors? The proper choice depends on the boiler system, plant layout, operating conditions and feedwater composition. In general, volatile amines are best suited to systems with low make-up, low feedwater alkalinity and good oxygen control. Filming inhibitors usually give more economical protection in systems with high make-up, air in-leakage, high feedwater alkalinity or intermittent operation. In most cases, a combination of these treatments may be the best to combat condensate corrosion. What characteristics should a good condensate corrosion inhibitor have? A good volatile neutralizing amine should have a favorable distribution ratio in steam and condensate so that it protects the entire steam-condensate system. It should have no insoluble reaction products and should be stable at high temperatures and pressures. A good filming inhibitor should be easy to disperse in water. It should be stable under usage conditions and form a thin, protective film without causing deposits in either the boiler or steam-condensate system

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Condensate Corrosion--Factors and Control Carbon Dioxide Breakdown of carbonate and bicarbonate that enter the boiler is the main source of carbon dioxide. Left unchecked, this can result in low pH condensate. This has been observed as grooving in sections of condensate lines that are not completely filled with water. Oxygen Oxygen can enter a condensate system by many sources even if the deaerating heater is functioning properly. The oxygen, at its worse, can result in deep pitting of condensate lines. The combination of oxygen and carbon dioxide corrosion can be particularly troublesome in causing corrosion products to be produced and transported to the boiler. Velocity Although often not controllable, high flow rates within the condensate system can produce extremely severe corrosion conditions. This flow-assisted corrosion is accelerated at low pH and can be minimized by keeping the pH above 9.0. Other gases Other gases that can be corrosive and present in the condensate system include ammonia, hydrogen sulfide, and sulfur dioxide. The most common of these is ammonia. Copper corrosion can be as serious as iron corrosion and is made even more serious in the presence of copper complexing agents such as ammonia. Again, oxygen in combination with these gases increases copper corrosion. Neutralizing Amines Neutralizing amines, when fed to the boiler, volatile with the steam and enter the condensate system. These amines are weak bases and will therefore neutralize any carbon dioxide present and will raise the pH of the condensate. If oxygen levels are very low, these neutralizing amines can, by themselves, effectively control condensate corrosion. However, knowing which ones to feed, how much, and how to control can be a difficult and confusing decision for the typical user. There are more than a dozen amines in common use. Each amine is unique in certain characteristics, each of which affect how the amine functions at a given point in a given condensate system. Those amine characteristics include basically value, molecular weight, distribution ratio, and hydrolytic thermal stability. Since it is necessary to prevent corrosion from the point of initial steam condensation to the far ends and back of condensate systems, a blend of neutralizing amines is normally fed. Volatile Passivating Agents If oxygen is present, the neutralizing amines alone will not control corrosion. Fortunately, chemical treatments have been developed which will transport with

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the steam and will, in addition to possibly reacting with oxygen, function as Passivating agents to prevent corrosion. But as is often the case, such new alternatives bring with them a whole new set of potential problems and set of rules. Which product to use where, when, and how are questions that are best answered by an expert in water treatment chemistry who is also highly knowledgeable about your system. Control and testing are the main problems with these Passivating agents. That is why corrosion monitoring, always important, becomes even more so when treatment results depend on a passivation chemical. Monitoring Corrosion monitoring is a major task for any water system. Relative pure waters, like condensate, make the task even more difficult. Some of the methods used and recommended by Thermidaire Consultants include the following: Test Coupons Steel and copper corrosion coupons have been used in condensate systems for many years. While there are concerns as to how accurately they reflect the actual corrosion rate within a given system, the do provide a good relative measure of trends in long term corrosion. A consistent, continuing program using coupons at the same locations and for the same duration of time is therefore most meaningful. The locations and plumbing for the coupons must be carefully engineered to avoid meaningless results. pH Monitoring While not a direct measurement of corrosion, continuous measurement of condensate pH can be very helpful in systems that depend on neutralizing amines for pH control. Other monitors, such as for conductivity, are also helpful to guard against condensate contamination. Location of sample points and method of sampling are critical and should be established by a qualified water treatment engineer. Iron and Copper Testing Another old but proven effective standby is iron and copper testing. The sample points, method of collection, and analytical procedures are more critical in trace metal testing than in any other analysis. Incorrect results are much worse than no results at all. The sample program should be established to collect samples at a pre-determined interval. The final feedwater represents the corrosion products load actually entering the boiler and can be a good indicator of the expected cleanliness of boiler surfaces over a period of time. Composite as well as spot samples should be taken. However, since the slightest change in flows can make sample results worthless, any composite samples collected should be collected from a continuously flowing sample and with a proven condensate composite sampler.

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Corrosion Test Monitors Electronic corrosion test monitors have now been developed that can be effectively used in condensate systems. Older corrosion test meters were not capable of this because of the need for the water being tested to exhibit a minimum conductivity. As with any of the monitoring methods, results from these should be evaluated over a long period of time and compared with prior results versus actual inspections. Monitoring of your condensate is essential toward protection of, not just the condensate system itself, but more importantly, to the continued reliability of the system boilers.

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