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MIL-STD-810 Method 521 Icing/Freezing Rain

MIL-STD-810G Method 521, Icing/Freezing Rain testing outlines the test procedures and operating conditions for evaluating the ability of equipment to withstand the effects of icing and freezing rain. This method is important for ensuring that equipment remains functional and reliable in cold and icy environments.  This method also provides tests for evaluating the effectiveness of de-icing equipment and techniques, including prescribed means to be used in the field. 

Under MIL-810G, Method 521 the team at Clark Testing typically subjects equipment to controlled conditions that simulate the formation of ice and freezing rain in a thermal chamber. The purpose is to assess how well the equipment can continue to operate and maintain its performance under these adverse conditions.  

In setting up the test plan, our test engineers will examine the requirements documents and applying the tailoring process of this standard to determine where icing/freezing rain is anticipated in the life cycle of the equipment to confirm the need for this method and to place it in sequence with other methods. This method is designed to determine if equipment can operate after ice accumulation from rain, drizzle, fog, splash or other sources.  

When ice removal is required before operation, use integral deicing equipment or expedients normally available to the user in the field. Clark can also evaluate deicing equipment and expedients to assess their effectiveness and the potential for damage that may degrade performance. 

When preparing the test plan and actual test, The Clark test engineering team will consider several factors including: 

  • Whether or not the equipment receives icing on all sides and the top or test the equipment in its deployment configuration. Also, if required, perform tests in other configurations such as for shipping or outside storage. 
  • Test temperatures used to produce the required environmental conditions are recommended in the test procedure.  
  • The recommended temperatures of the chamber and water may have to be adjusted for different size facilities to prevent premature freezing of the water droplets before they come in contact with the test item. 
  • The water delivery rate to produce a clear, uniform coating of glaze ice. Any delivery rate that produces a uniform coating of glaze ice is acceptable, however, a water delivery rate of 25 mm/h is suggested in the test procedure and is based on data from previous testing. 
  • Various type of water delivery method or water delivery systems can be used as long as the water is delivered as a uniform spray.  These methods include: 
  • Nozzle arrays directing spray to the top, sides, front, and rear of the test item. 
  • Nozzle arrays that direct spray straight down onto the test item. Side-spray coverage is achieved by using wind or an additional hand-held nozzle. Minimize any wind in order to maintain uniform ice accretion. 
  • A single nozzle directing the spray over the appropriate surfaces of the test item. 
  • Droplet size may have to be adjusted for different size facilities. A fine spray in the range of 1.0mm to 1.5mm diameter nominal droplet size has produced satisfactory icing in some facilities. 
  • Ice thickness unless specifically measured data for the anticipated situation are available, the following ice thicknesses are recommended:  
  • 6mm (0.24 in) - represents general conditions, light loading. 
  • 13mm (0.5 in) - represents general conditions, medium loading. 
  • 37mm (1.5 in) - represents heavy ground loading and marine mast loading. 
  • 75mm (3 in) - represents extremely heavy ground loading and marine deck loading. 
  • Operational Considerations. 
  • Some equipment covered with ice may be expected to operate immediately without first undergoing deicing procedures; other equipment would not be expected to operate until some form of de-icing has taken place (e.g., aircraft ailerons (flaps) prior to flight).  
  • Ice removal, if required, may include built-in ice-removal systems, prescribed means that could be expected to be employed in the field, or a combination of these. 
  • The correct operation of anti-ice systems such as pre-heated surfaces. 

General test procedures the Clark test team will employ for Method 521 Ice/Freezing Rain testing includes: 

Placing customer’s equipment in Clark’s environmental chamber which is capable of controlling temperature, humidity, and other relevant parameters. The customer’s test specimen is positioned in the test chamber, and instrumentation or sensors (thermocouples) are installed to monitor various thermal parameters. 

The test chamber is programmed to the desired temperature and humidity conditions based on the test plan to create icing and freezing rain conditions.  Our test technicians will initiate water sprayers or other mechanisms to introduce droplets onto the test specimen. These droplets freeze upon contact with the equipment, forming ice layers. 

The standard may define specific temperature and humidity profiles for the testing which can vary based on the intended use and environment of the equipment.  The test may also involve cyclic exposure subjecting equipment to alternating periods of icing and thawing to simulate realistic conditions. 

During and after the exposure we will conduct functional testing to validate performance and any changes in its characteristics.  The environmental test data, including functional testing, is analyzed to assess how well the equipment performed under icing and freezing rain conditions and will be included in the test report. 

Please contact the test engineering team at Clark Testing so we can help ensure that your equipment will operate, function, and maintain its performance after withstanding the impact of Ice & Freezing Rain due to conditions in the operating environment.  Call or email the Clark Dynamics Test Laboratory for assistance in developing a test plan and conducting the appropriate test to validate your equipment in accordance with MIL-STD-810G Method 521 Ice/Freezing Rain Testing. 

Test Set Up

In house custom design and fabrication capabilities (machining and welding) to ensure test fixtures accurately simulation environmental conditions.  FEA capabilities to support fixture design along with welding, fabrication & machining services.  Multiple vibration adapter plates and prefabricated test fixtures help to streamline the testing process.

Instrumentation capabilities including accelerometers and strain gages with multi-channel control and data acquisition equipment ensuring accurate test data is being recorded.  All instrumentation and equipment is provided with measurement uncertainty and compliant   with Clark’s ISO 17025-2017 Quality Program.

Lab technicians and engineers record daily test activities to register all activities, events, and responses during the test.  The daily test logs along with test data, pictures and test procedures are included in comprehensive test report that is the industry standard.

 We work closely with you to validate engineering, ensure quality, analyze test spectrums, and execute accurate testing programs for successful qualification and marketing of your product.

We work closely with you to validate engineering, ensure quality, analyze products and qualify equipment while supporting the time constraints and product cycles that are vital to your success.

Paul Heffernan, CEO of Clark Testing