CLOSED LOOP INHIBITORS ************************

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1 CLOSED LOOP INHIBITORS ************************ Purpose: To protect the metallurgy of construction in the closed loop system from corrosion and scale formation through the addition of scale modifiers, corrosion inhibitors and/or through the use of pretreatment equipment. A closed system is defined as any water system that is used to transfer heat which is not open to the air and has less than 5% make up due to system volume loss per day. This includes systems which are used to remove the heat from air compressor inner coolers and after coolers, perimeter heating systems, hot water closed loop systems, chilled water closed loop systems and any other closed loop system which uses water as the medium for the transference of heat from one heat exchanger to another. The advantages of a closed system over an open recirculating system, in the area of heat removal through cooling, is that there is a small make up requirement in the closed system. This means that once the desired water temperature has been obtained, the temperature is very easy to control. It also means that the system is not does not continually saturate itself with oxygen, and that it does not refoul itself with biological contamination on a continuous basis. This reduces the potential for the system to experience deposit formation, corrosion and biological fouling. It does not however prevent these conditions from occurring. SCALE: Scale is formed in a closed system where the water contains hardness (calcium and magnesium dissolved in the water) and this water is exposed to an increase in water temperature. The formation of scale is not a usual occurrence in a closed system. It comes into play when the system is used to cool high heat systems. This could be a heat exchanger that has skin temperatures above 180 F or a cooling heat exchanger on a reciprocating air compressor. As the water is heated up, the ability of the

2 hardness salts to stay in solution is decreased. This means that as the water is heated, the calcium and the magnesium will start to drop out of the water and form scale. When scale does form, it can dramatically reduce heat exchange efficiency and cause severe wear on internal metal components. The removal and the prevention of the scale is the normally desired route that a plant should take. Once the scale has been found, it can be removed rapidly with the use of mild acids as Sulfamic Acid or chelating agents as; citric acid, HEDP or EDTA. Circulation of these compounds will cause the scale deposit to be dissolved and then can be flushed out of the system. Now that the scale has been removed, the prevention of future scale is accomplished with the use of dispersant and chelating agents. The dispersant will keep the solids in the water in solution, while the chelating agents prevent the hardness salts from coming out of the water and forming deposits. Scale preventative programs are controlled with the use of either a phosphonate test when using HEDP or the use of a tracer as Molybdate when using some of the all organic or all dispersant based programs. CORROSION: The most common problem usually found in a closed loop system is corrosion. Corrosion can be caused by oxygen reacting with the system metal, galvanic activity between two dissimilar metals, low ph, or from byproducts of bacterial activity. In all of these cases, there is a metal loss which can result in leaks and failure of the system. The dissolved oxygen in the water will start to react with steel bearing metals in the system as the temperature of the water increases. This causes the formation of metal oxides which will then be seen as black water, brown sludge and leaks in the piping. Control of the oxygen is accomplished by using an oxygen scavenger as sodium sulfite in hot water boilers, or with the use of both the silica and the nitrite based inhibitors which set up a protecting film on the metal. Where you have two dissimilar metals as steel and copper or copper and aluminum, the metals will set up a galvanic action similar to that found in a battery and use the water as the media for conducting the electrical current. The result is rapid corrosion of the sacrificial metal and pitting of the other metal surface. A sludge is formed which impedes heat transfer and by the time that it is found, the metal in the system has failed. The result is costly repairs. BACTERIAL ACTION:

3 Bacteria are found in all waters used for closed system make up. In the chilled water systems, the growth is usually very slow and is not normally a problem. When using biodegradable corrosion inhibition programs or nitrite based programs, a nutrient for bacteria is introduced into the closed system. This will allow the growth of bacteria. In hot water systems that maintain a temperature below 180 F, the problem with bacteria growth is more prominent. Once a bacteria growth has established itself in the system, then the corrosion inhibitor will start to break down as it is consumed by the bacteria. The byproduct of the bacteria is an acidic excrement which is deposited at the bacterial contact with the metal of the system. This causes corrosion at that point and eliminates the corrosion inhibitor in the system. The first indication of bacterial attack is that the water starts to have an odor to it. Then the water starts to turn black. Once this has been seen, it is important to flush the system out with a biocide and then charge the system with the proper amount of corrosion inhibitor. PROGRAMS: The basic types of programs which are used to protect a closed loop system are: CHROMATES SILICA NITRITE/BORATE/SILICA SODIUM SULFITE/DISPERSANT ORGANIC DISPERSANT ORGANIC DISPERSANT/POLYDIOL CHROMATE: based programs are effective in both hot and chilled water systems. The chromate residual is maintained from ppm for chromate or ppm when using an Ultra Low Chromate (ULC) program. Chromate is the most effective closed loop product for the prevention of corrosion and it will not allow the formation of bacterial growth in the system. It can be controlled with a color (yellow) intensity comparator. Chromate should not be used in systems that have mechanical seals unless the chromate residual in the system is below 250 ppm. Otherwise, it will cause erosion of the seals and they will leak. Chromate is a very abrasive material and at high levels, it can cause erosion of most seals. When seal leakage occurs, repair the seal and reduce the level of chromate in the water. The problem is that chromate is so stable and toxic that it has been virtually outlawed by the EPA in this country. The use of any chromate requires that any leakage of treated water or discharge be passed through a chromate reduction system and the reduced chromate

4 is to be disposed o as toxic waste. SILICA: programs are run with a residual from ppm as silica and should be maintained within a ph range of for maximum effectiveness. Silica will protect steel, galvanized steel, copper, admiralty brass, and copper-nickel alloys from corrosion. Silica can be used in food plants as a food grade silica for protection from corrosion, however, it is usually used in conjunction with other inhibitors for best results. NITRITE/BORATE/SILICA: programs are the most commonly used programs for both chilled water and hot water closed loop systems. Using nitrite as the tracing agent, the program is maintained from ppm as sodium nitrite in the closed loop system. This type of corrosion inhibitor is compatible with ethylene and propylene glycol, so it can be used in virtually all of the chilled water systems in use today. The product uses the anionic nitrite to induce the metal surface to form a hydrated oxide film. This prevents the attack of oxygen on the metal. The borate is a inhibitor for steel that prevents galvanic and oxidation reactions. At 2.0% of borate in a solution, steel will not corrode. The silica is used to protect most of the metal surfaces in the system by forming a film that prevents any reactions with the metal surfaces and the corrosive agents found in the water. The use of TTZ an azole in a product with Nitrite/Borate/Silica allows the product to have increased corrosion inhibition for all of the copper bearing metals in the system. Where aluminum is in the system, Nitrite will act in a very corrosive manner to the aluminum and the product should have Sodium Nitrate instead of Sodium Nitrite. Sodium Nitrate is a corrosion inhibitor for aluminum. Bacteria can react to use nitrite as a food source, and should be watched for when using this type of program. Odor and black water will appear. When this occurs, a nonoxidizing biocide as polymerized quat should be used to kill the bacteria. The system then needs to be flushed and recharged with sufficient corrosion inhibitor. SODIUM SULFITE/DISPERSANT: programs are used in hot water closed loop systems only. In these systems, the primary cause of corrosion is usually oxygen attack on the metal. The sodium sulfite acts as an oxygen scavenger and absorbs the oxygen out of the water. The dispersant that is blended into the product will act as a cleaning agent and keep the solids from the water in suspension. The end result is that the system stays clean and free of corrosion. The sodium sulfite should be maintained between 100 and 200 ppm in the closed loop system for best results. This program can be used in a hot water system where the Nitrite/Borate/Silica product

5 has caused seal leaks and valve stem wear to stop the wear on the valve stems and seals. This program will not be effective in chilled water systems and another type of program should be used in this case. ORGANIC DISPERSANT: programs used dispersant and organic corrosion inhibitors. They are designed for use where the nitrite based programs are causing seal problems, and a biodegradable approach is needed. This program uses a blend of dispersant to prevent scale formation and solids build up, mild chelants as HEDP and Gluconate to prevent galvanic attack and iron fouling, TTZ to protect the copper alloys in the system and in some cases, silica as a general corrosion inhibitor. The program is usually all organic and environmentally safe. It is more expensive than the nitrite based programs but has value in being safer to discharge. The other problem with the organic based programs is bacteria attack. If a product is food grade, biodegradable or organic in nature, it is a natural food source for bacteria. Total bacteria slides should be run on this type of program every few months to be sure that bacteria is not taking hold in the system. If bacteria is present, it will rapidly consume the dispersant and the corrosion inhibitors. Remove bacteria with the use of biocides as has already been described. Sodium Molybdate is used in many of these programs as a indicator of the product level and as a corrosion inhibitor. When it is used, Sodium Molybdate residuals of ppm are used based on the blend of the product. ORGANIC DISPERSANT/POLYDIOL: programs are basically the same as the organic dispersant programs, except that a polydiol (PEG - Polyethylene Glycol) is added to the product. This is a very active surface active agent that forms a protective film on the metal surfaces of the system. The product is very difficult to blend and is relatively unstable if stored over 90 days. It can cause the formation of a very sticky sludge if over fed and can cause the slow loss of heat exchanger transfer efficiency as it forms a oil-like film over the metal surfaces. The product is very effective, but needs to have more work done on it before it can be used easily in the field. APPLICATION:

6 PROGRAM TYPE: APPLICATIONS AREAS CHROMATE USE ONLY WHERE INDUSTRIAL USE IS REQUIRED. NEVER IN A FOOD PLANT. SILICA NITRITE/BORATE/SILICA SODIUM SULFITE/DISPERSANT ORGANIC DISPERSANT ORGANIC DISPERSANT/POLYDIOL FOOD PLANT - DAIRY - HOT WATER CHILLED WATER HOT WATER - CHILLED WATER COMPRESSOR INNER COOLER HEATING (HOT WATER) AIR CONDITIONING CHILLED GLYCOL SYSTEMS HOT WATER HEATING HOT WATER HEATING CHILLED WATER AIR CONDITIONING CHILLED COMPRESSOR INNER COOLER HOT WATER HEATING CHILLED WATER Compliments of GUARDIAN CHEMICAL SPECIALTIES CORP.