ASHRAE Journal - April 2011 - 58

fected, but is only evident when the system fails. It is important to remove the moisture from the system. Following deep dehydration and evacuation of a refrigeration system during installation can significantly remove the moisture from the system. Any traces of moisture can further be countered by providing a filter drier in the refrigerant liquid line. The core of the driers should be regularly replaced.

Corrosion by Moisture Surrounding the System
In marine refrigeration plants moisture present outside the system also causes considerable corrosion. Corrosion under insulation (CUI) of carbon steel pipes and the evaporator shell10 is a typical example of corrosion by moisture surrounding the system. Unfortunately, CUI is difficult to detect as the metal surface is covered under insulation. The water formed from condensation of moisture expands during freezing and damages the insulation. The damaged insulation becomes more susceptible to further corrosion. All joints and surfaces should be carefully sealed to keep out atmospheric moisture. Applying corrosion resistant paint and installing a good closed cell insulation material that is tightly bound to the pipe can help control CUI. During maintenance, the damaged insulation should be inspected, repaired or replaced. In refrigeration applications below 0°C (32°F), a proper drain arrangement with defrost heaters must be provided. The electrical panels should incorporate space heaters. The cable entry11 to electrical panels should be placed to avoid any chances of water dripping inside. The IP Codes or International Protection Rating for electrical equipment must be followed.

with a soap solution. Routinely inspect the duct for moistureinduced corrosion damages. Refrigerant piping is joined by welding and brazing. Both processes are heterogeneous and are susceptible to microgalvanic corrosion. The joints retain residual stresses and matrix heterogeneity. Heating these joints to appropriate temperatures, which are below the transformation temperature range, may reorganize the microstructure uniformly and deactivate the highly stressed sites. Such structural uniformity and stress matching reduces the microgalvanic corrosion.

Summary
Designers can tackle corrosion problems by designing heat transfer processes better, controlling the flow behavior of fluids involved, selecting corrosion resistant construction materials and choosing appropriate manufacturing methods. In addition, designers also need to consider ease of inspection and maintenance and optimization of capital and operating costs. A designer’s dream can become a reality only by proper installation and operation of a system. Hence, care must be taken during installation and operation to minimize corrosion.

Acknowledgments

The author wishes to thank Kirloskar Pneumatic Company Limited, Pune, India, for providing an opportunity to learn and design marine refrigeration and air-conditioning systems.

References
1. U.K. Ministry of Defence. 2000. U.K. Defence Standard 02-738, Metals & Corrosion Guide. 2. EPRI. 1983. “Current Cathodic Protection Practice in Steam Surface Condenser.” CS-2961, Project 1689-3. Electric Power Research Institute. 3. Morgan, J. 1987. Cathodic Protection. Houston: National Association of Corrosion Engineers. 4. Det Norske Veritas. 2005. “Recommended Practice DNV-RP-B401, Cathodic Protection Design.” 5. U.K. Ministry of Defence. 2006. U.K. Defence Standard 02327, Requirements and Guidance for the Procurement of Pumps for Auxiliary Systems. 6. Pearson, A. 2008. “Stress corrosion cracking in refrigeration systems.” International Journal of Refrigeration 31(4):742 – 747. 7. U.K. Ministry of Defence. 2007. U.K. Defence Standard 00-970 Part 7/2, Design and Airworthiness Requirements for Service Aircraft, Section 4 Detail Design and Strength of Materials. 8. Sommariva, C., H. Hogg, K. Callister. 2003. “Cost reduction and design lifetime increase in thermal desalination plants: thermodynamic and corrosion resistance combined analysis for heat exchanger tubes and material selection.” Desalination 158:17 – 21. 9. U.K. Ministry of Defence. 2009. U.K. Defence Standard 02-781, Protection of Seawater System Pipework and Heat Exchanger Tubes in HM Surface Ships and Submarines. 10. Dettmers, D.J., D.T. Reindl. 2007. “Mechanical integrity and carbon steel refrigerant piping.” ASHRAE Journal 49(10). 11. U.K. Ministry of Defence. 2008. U.K. Defence Standard 02-514, Guide To Cable Entry, Termination And Junction Components For Equipment. 12. Kirk, W., A. Tuthill. Accessed Feb. 2011. “Condenser and Heat Exchange Systems.” http://tinyurl.com/4krlvtg. ashrae.org April 2011

Corrosion Control in Piping and Ducts
Corrosion affects refrigerant piping, chilled and seawater piping and HVAC&R ducts. The higher flow rates in chilled and seawater piping and in seawater tubes are limited by erosion. But low flow rates are also damaging and cause under deposit corrosion.12 Erosion problems in condenser water heads can be minimized by sizing the water heads for 10% to 15% extra capacity and carefully deciding the nozzle entry. Selecting suitable corrosion resistant construction material controls corrosion of chilled water and seawater piping. Titanium and cupronickel pipes allow higher velocities without erosion problems. However, these materials are costly. The pipes can be joined together by flanges and stubends. With this arrangement, flanges are prevented from coming in contact with seawater. Therefore, carbon steel flanges and cupronickel stubends are common for marine applications. This also helps reduce capital costs considerably. Steel sheets are used to make air ducts. To inhibit corrosion during transportation and storage of the ducts, they are coated with a thin film of oil. However, this coating may trap dirt particles and cause problems with ensuring acceptable indoor air quality. Before installation, remove the oil coating by washing
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ASHRAE Journal - April 2011

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