Heat Exchanger Care and Water Quality Guide 015-164-000 C l
Copyright information Trademark information © 2005 MTS Systems Corporation. All rights reserved. MTS is a registered trademarks of MTS Systems Corporation. DTE and SHC are registered trademarks of Mobil Corporation. Molykote is a registered trademark of Dow Chemical Corporation. Contact information Publication information MTS Systems Corporation 14000 Technology Drive Eden Prairie, Minnesota 55344-2290 USA Toll Free Phone: 800-328-2255 (within the U.S. or Canada) Phone: 952-937-4000 (outside the U.S.
Content Heat Exchanger Care 5 What is a heat exchanger? 5 What are the major components of my heat exchanger? What ambient conditions are required? 8 What is the life expectancy of my heat exchanger? What causes heat exchanger failure? 6 10 10 How can I prevent heat exchanger failure? 11 Mechanical failure with chemically induced corrosion 13 How do I know when I have a heat exchanger failure? 14 How can I improve the life of my heat exchanger? 15 What regular heat exchanger maintenance is r
Content Heat Exchanger Care and Water Quality Guide
Heat Exchanger Care MTS hydraulic power units (HPUs) are equipped with heat exchangers that are designed to remove 100% of the HPUs heat load. Heat exchangers usually provide a long service life with little required maintenance because they have very few or no moving parts. Often, however, the heat exchanger is a neglected component of the HPU until it fails. A heat exchanger failure can result in a costly and time-consuming cleanup, especially when your cooling water supply is mixed with hydraulic fluid.
What are the major components of my heat exchanger? Hydraulic fluid-towater Plate design The plate design hydraulic fluid-to-water heat exchanger has no moving parts. It consists of a series of corrugated stainless steel plates brazed together. The direction of the herring bone design of the plates alternates to provide maximum turbulence and therefore maximum cooling efficiency. The plates are brazed together to provide strength and a compact package.
Hydraulic fluid-to-air • Shell–the shell is a seamless, nonferrous tube, usually made of brass. Both ends are welded into the hubs. The shell encloses the baffles or fins very closely to prevent any bypassing and ineffective flow areas. • Tubes–straight, seamless, nonferrous tubes are usually made from copper, a copper-nickel alloy or stainless steel. • Tube sheets–brass tube sheets hold the cooling tubes in place. Tube sheets are bonded to the inside of the hubs.
What ambient conditions are required? Operating temperatures Water-cooled heat exchangers used in HPUs, operate at a minimum ambient temperature of 4°C (40°F) and a maximum ambient temperature of 40°C (104°F). Air-cooled heat exchangers operate effectively up to an ambient temperatures of 37°C (98°F). A nameplate specifying operating pressures and temperatures is attached to each heat exchanger by the manufacturer.
Water Chemistry Compounds found in water Allowable quantity (parts per million) Ammonia none Bacteria must be bacteriologically safe Calcium <800 ppm Chlorides <5 ppm Dissolved solids >50 but <500 ppm; limit to 150 ppm if abrasive solids present Iron 3 ppm Nitrates <10 ppm Nitrogen compounds none Oxidizing salts or acids none pH level 6–8.
What is the life expectancy of my heat exchanger? All heat exchangers have a finite life and must be considered an expendable component, subject to failure at some point in time. Properly used and maintained, your heat exchanger could last up to 20 years. What causes heat exchanger failure? Heat exchangers usually provide a long service life with little maintenance other than a routine inspection and cleaning. Fouling and corrosion are the main causes of degraded performance or failure.
Contaminated water supply The most likely cause of corrosion failure in heat exchangers is their use with cooling towers. These towers use fan propelled ambient air to evaporate a portion of the cooling water and thus cool the remaining water. This action transfers whatever air pollution exists into the cooling water. Also, since the towers are open to the environment, they are prone to collecting animal and vegetable matter which is damaging to heat exchangers.
• Chemically induced corrosion Freeze-Up: These failures can occur in a water cooled heat exchanger in which the temperature drops below the freezing point of the cooling water. Freeze-up results from failure to provide thermal protection, a malfunction of the thermal protection control system, or protective heater device, improper drainage of the unit for winter shutdown or an inadequate concentration of antifreeze solutions.
• Dezincification: This problem occurs in copper-zinc alloys containing less than 85 percent copper when they are in contact with water having a high oxygen and carbon dioxide content, or in a stagnant solution. The effect tends to accelerate as temperature increases or pH decreased below 7. Dezincification creates a porous surface in which the zinc is chemically removed from the alloy. The remaining copper has a sponge-like appearance.
Fouling due to accumulation of scale, solids, and algae Various compounds and marine growths present in cooling water will deposit a film or coating on heat transfer surfaces. The film acts as an insulator, restricting heat flow and protecting corrosive compounds. As a result of this insulating effect, temperatures go up and corrosion increases. • Scale is the result of dissolved minerals precipitating out of heat transfer fluids.
How can I improve the life of my heat exchanger? Routine inspections and maintenance enable you to slow the degradation effects in heat exchangers. The effects will always be present, however, and will sooner or later result in the necessity of replacing the degraded components.
Monitor the cooling water flow rate The easiest way to prevent fouling is by assuring that there is a sufficient flow of cooling water in all of the chambers. This will maintain a “self-cleaning” effect in the chambers, which also helps them retain their heat transfer characteristics. If you notice a decrease in the efficiency of your heat exchanger, inspect the filter or strainer and the chambers for signs of fouling.
WARNING • Be careful using sealant tape on pipe threads, which lessens the degree of resistance between mating parts, and results in a greater chance for cracking the heat exchanger castings. Do not over-tighten pipe connections when remounting the heat exchanger after you have disassembled it for maintenance. • When you are ordering replacement parts, mention the model and serial number of the heat exchanger, the model of the HPU and the original MTS job number.
Tube and shell heat exchangers 1. Clean all filters and screens. 2. Begin with an external inspection of the heat exchanger. Visually inspect for: • Dents or bulges in the shell • Extruded or damaged gaskets • Corrosion • Damaged flanges on the bonnets and hub or tube sheets • Stress marks in the shell • Signs of a previous repair • Leakage 3. After you have completed the external inspection, continue with an internal inspection of the heat exchanger: A.
Mechanical cleaning Complete the following steps if your internal inspection of the shell and tube heat exchanger indicates that you need to remove any sediment or light scale from the tubes: 1. Remove residues from the inside of the tubes with a rotary brush. Use a soft nylon brush to prevent scratches in the metal surfaces since any scratches will accelerate corrosion. 2. Flush the tubes with clean water to remove dirt and scale loosened during the brushing. 3.
5. Keep the motor outside surface of direct drive heat exchangers free of dirt and grease so the motor will cool properly. Make sure the cooling air over the motor is not obstructed. Pre lubricated ball bearing motors require no lubrication for extended periods of time. Follow the lubrication instructions attached to the motor and provided by the motor manufacturer. 6. The combination fan hub and sheave assembly on external drive heat exchangers is pre lubricated at the factory prior to shipment.
Acceptable Ranges for Copper Copper Concentration Indication 20–50 (ppm) Normal amounts >50 (ppm) Watch for additional trends in the hydraulic fluid analysis Sharp rise There is a problem which requires immediate action Look for the presence of hydraulic fluid in the cooling water, or water in the hydraulic fluid. MTS has water-in-fluid and fluid-in-water sensors available to aid in the early detection of contamination of your cooling water or hydraulic fluid. Contact MTS for more information.
Troubleshooting Symptoms HPU won't cool (hydraulic fluid-to-water models) Corrective Action • Verify the proper water connections: IN→IN OUT→OUT Heat exchanger is plugged Heat exchanger leaks externally Heat exchanger leaks internally 22 Troubleshooting • Verify that the water temperature vs. flow rate is correct for your model of HPU (refer to the MTS Hydraulic Power Supply Product Manual that came with your system). • Verify that the operation of the water saver valve is correct.
m MTS Systems Corporation 14000 Technology Drive Eden Prairie, Minnesota 55344-2290 USA Toll Free Phone: 800-328-2255 (within the U.S. or Canada) Phone: 952-937-4000 (outside the U.S. or Canada) Fax: 952-937-4515 E-mail: info@mts.com http://www.mts.
