Descaling Industrial Washers

It is easy to neglect cleaning and maintenance of a washer. The time required to clean the washer does not contribute directly to production but washers occasionally need extra cleaning, replacing the chemical solutions is not enough to keep a washer in good working order.

Overtime, processing equipment will have a build up of scale and dirt. They need cleaning and maintenance in order to keep them working properly and efficiently. This is critical with spray washing equipment as nozzles and risers and pumps can build up water scale and their efficiency can drop drastically over time. The interior diameter of risers and headers can be substantially decreased by scale build-up. Temperature transfer from heating tubes will be more effective after descaling.

Power washing or rinsing the washer alone will not remove hard water scale, oil, and grease that can build up inside risers, on the walls of the tank, on canopies, and on heating tubes or heat exchangers.

Scale can interfere with the proper operation of a washer and cause problems processing parts such as insufficient cleaning or coating. It can also cause higher chemical or heating costs.

A great deal of time may be spent cleaning nozzles when a good descaling of the washer will remove the scale that breaks off and clogs the nozzles. Time spent descaling is more than balanced by the amount of time that is spent cleaning out nozzles.

The nature of scale will vary from application to application but generally it will come from hard water salts, sometimes complicated by the chemicals used in the process. Certain cleaning chemicals may deposit silicate scales which are difficult to remove. Scales may be carbonates, silicates, phosphates, or metal oxides such as rust. Each of these may need to be handled slightly differently from each other.

Descaling chemicals generally fall into two different categories. Alkaline and inhibited acidic descalers.

Acidic descalers are used at room temperature to 140 degrees F. They tend to work faster than alkaline descalers. Acidic descalers are inhibited with materials that prevent attack on metals but do not protect the scale. Most inhibitors have a temperature that they begin to decrease their inhibition. With acidic descalers, temperatures in excess of 140 should be avoided and temperatures in excess of 110 should be used with caution.

Alkaline descalers must be used with temperature to be more effective. Generally the hotter the better. Alkaline descalers take longer to work and work much more effectively with certain scales such as silicate cleaner residues.

A washer may need top be evaluated on the basis of how bad the scale and corrosion of the washer actually is. Scale can a sometimes cover up holes in the wall of the washer and the heating tubes. Because of the potential for leaks, absorptive materials or some process to clean up chemical spills that may occur must be available.

You should have the ability to weld or otherwise seal any holes which may occur during the descaling process. Because inhibitors only protect the metal from attack they do not protect any rust on the surface of the metal. Older washers may have a substantial amount of rust and scale and it may be covering potential leaks in the wall of the washer.

There are many variations on the descaling process and some steps may not be necessary with every washer however this process outlined here represents some of the best practices.

Because there may be problems which may occur during a decaling process it should be performed when there is plenty of time to complete the process of both descaling and cleanout of the washer. The process is labor intensive at the beginning and the end of the process but the middle is essentially labor free. Scheduling of workers should be done accordingly. It may take anywhere from 4 to 12 hours or more depending on the size of the washer and the severity of the scale build-up.

It is usually recommended that this process be done when there are fewer personnel in the area to assure that no one is exposed to any acid fumes that may escape from the washer. Any ventilation such as exhaust to the outside of the plant should be utilized to prevent build-up of fumes in the plant.

The most common inhibited acid is hydrochloric acid. During the process this acid is neutralized essentially creating sodium chloride which is a salt. The salt must be completely removed since it can cause subsequent corrosion on processed parts especially if the rinse stage is not completely cleaned, so plenty of water should be used to rinse the tanks multiple times at the end of the process.

The process can vary from washer to washer but generally breaks down into several steps.

The washer should be given a general clean up. The existing chemical solution must be removed fro the tank. Usually a pressure washing of the washer will remove some soils and any loose parts should be removed from the bottom of the processing tanks.

The washer must be prepared for descaling. Any filtration system should be evaluated to see if it is safe with acid solutions. Any water refill valves should be evaluated to see if they are acid safe and should be turned on or off during the descaling process. Generally the water refills should be turned off.

Copper alloys may be a problem as the copper can be affected by the descaling solution. Any copper nozzles, valves, or float valves should be removed from the washer.

Since the descaling process can create a mist which can spread throughout the plant and may cause rusting of equipment in the area of the washer it is often a good practice seal the entrance and exit of the washer. The openings at the should be covered to prevent fumes for escaping. This may be as simple as closing the doors on the washer or taping sheets of plastic over the entrances. This does not need to be an air tight seal but it will prevent the vast majority of the mist from reaching the rest of the plant. If only a single stage is being descaled, the adjacent stages may be run with water the act as a fume barrier. These stages should be checked after the descaling process to assure that there has not been transfer of descaling solution into them.

The washer should be filled up about half-way with water and then the proper amount of descaling chemical should be added. Then the tanks should be filled to operating level. Custom Designed Chemicals Acid Descaler should be used at approximately 10% by volume. It is an inhibited acidic material and the MSDS should be read carefully prior to use. The inhibitors and surfactants protect the washer metal form attack and held wet the surfaces to remove the soils. It will not have an appreciable attack on steel and stainless steel.

Higher temperatures will descale faster and have less foam. Very high pressure washers may require the use of a slight amount of defoamer.

The washer needs to be run as long as needed to complete the descaling process. This will vary from 4 to 12 hours depending on how bad the scale is and the temperature at which the washer is run.

If the temperature is in operating range and there is no corrosion that is covering up leaks in the washer, it does not hurt the washer to run it fro an extended period of time.

The washer should be checked occasionally to make sure it has not developed a major leak of that the nozzles have not completely plugged up.

Screens should remain in the washer but must be monitored to make sure they do not plug up causing possible burn out of the pump system.

There are different schools of thought on how to handle nozzles. Whether or not to remove the nozzles during the descaling process will vary from operation to operation. If the nozzles are not removed they can quickly plug up with scale which has been loosened during the decaling process.

Running with no risers may burn out certain pump motors that need some back pressure to operate properly. Other types of pumps will burn out if there is excessive back pressure due to clogged nozzles

However once the nozzles are removed the pressure will drop and the distance that the solution will spray will decrease and the descaling solution may not reach some areas of the washer.

It is often good practice to remove the nozzles high up on the risers. This assures solution flow through the risers without having an extreme drop in pressure. Running the washer with plugged nozzles is an easy way to burn out a pump motor.

Sometimes it may be practical to run the washer for an hour or so without nozzles so that the bulk of the scale is dissolved, then replace the nozzles so the solution can reach the walls of the washer.

Nozzles can generally be cleaned off line also by using a bucket full of 20 to 100% descaling solution. Acid descalers will clean nozzles at room temperature, alkaline descalers should be heated to accelerate descaling.

During the descaling process it is often useful to stop the process in the middle, let the washer clean of fumes and mist, rinse the walls and ceiling of the washer (primarily the ceiling) and go into the washer to see how the process is proceeding. This gives you the opportunity to evaluate how much descaling still needs to be done and estimate how much time the washer needs to still be run. It is also a good time to open up any nozzles that have been plugged up.

After descaling the solution will have dissolved metal and hard water salts. It will be acidic however the acidity level will be decreased from the reaction with the scale. It is not practical and nearly impossible to determine how much acid will be neutralized during the process.

When the process is complete the solution can be pumped out of the tank and be disposed of, or it can be neutralized slightly to make a less hazardous solution, or it can be completely neutralized in the washer itself and sent down the drain.

Neutralization should be done cautiously as it is easy to overshoot the neutralization point making the solution too alkaline to send down the drain. This will also cause precipitation if iron hydroxides instead of other salts such as iron phosphate and this will cause the formation of a brown gelatinous iron hydroxide to precipitate on the walls of the washer. This coating generally dissolves in the weeks after the descaling process but can lead to an increased consumption of chemical in the process after the washer has been recharged,. It is much easier and more efficient in the end to take time during the neutralization not to over shoot the required pH. Being in the lower end of the scale is usually preferred over the higher end of the range because of this. The washer should be run during the neutralization process as areas of lower ph may remain in the tank.

After neutralization the solution can be hauled away or sent down the drain.

After draining and neutralization, the entire system should be power washed, including tanks canopies, heating tubes, and any conveyor systems.

The washer should be inspected to see if any additional repairs are needed. It should be filled and allowed to run for a sufficient amount of time to properly rinse the washer.

Quick disconnect nozzles may be used to make the cleaning process easier and faster.

Generally the exhausts are run through the descaling process however galvanized ductwork or non-acid proof exhaust fans may require the exhaust system to be turned off. After an acidic descaling there may be silicate or silica residues remaining on the side of the washer. Some organic and carbon deposits may remain in the washer.

Certain materials for example zinc phosphate tanks may require a customized descaling chemical. Certain applications may require nitric acid or citric acid containing products

If a washer is just processing steel then there should be little or no hazardous metals in the scale. If an excessive amount of zinc or galvanized metal has been run through the washer then there may be some of these metals in the scale and the solution may be considered a hazardous waste. Chromated parts such as brite dipped zinc or chromated aluminum may also create hazardous wastes. These neutralized descaling solution may not be sent down the drain.

CALL US TODAY AND WE CAN DISCUSS YOUR DESCALING NEEDS 312-550-7083

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