Engineers must often devise a method to keep the components of their outdoor systems safe from the effects of the environment, whether they're electrical or any other kind of moisture-sensitive components. Various options exist for providing this type of protection, and selecting the proper method depends on several project-specific factors. The material chosen to form a barrier between the environment and the critical component is of primary importance, followed closely by the details required by the specifications of the individual article being designed. The designer must consider factors such as material properties, durability, manufacturability, availability, and cost.
The issues discussed herein apply to any system which will encounter exposure to the elements of nature such as rain, wind, dust, sunlight, humidity, and high and low temperatures. A barrier to these elements is often provided by an enclosure which protects any sensitive electrical or mechanical components, however design circumstances may require that one or more working components double as the environmental protection. Enclosures are commonly used to guard outdoor electrical components such as switch boxes, transformers, display panels, etc. but a bit more creativity must go into designing environmental barriers such as car headlight lenses, aircraft windshields, and ship porthole windows. While the functions of these components can be highly variable, they must all be able to withstand the degenerative influence of a multitude of weather conditions.
When choosing the material to be used for parts which will be exposed to the environment, one must consider the degree of corrosion protection needed, weatherability, and service life. If it is deemed necessary to use metal due to general high strength and ease of manufacturability, the most practical choice is painted galvanized carbon steel. If further corrosion resistance is required other metal alloys such as stainless steel or different types of aluminum may be used. When a lower strength and price option is adequate, plastics such as polycarbonate, polyester, and PVC may be used. If both increased strength and corrosion resistance are needed, modern composite materials such as fiberglass reinforced polyester might be the best choice.
Choosing the appropriate material for an enclosure or external part of a system must be done on a case-by-case basis. The most important thing for the designing engineer to consider is the characteristics of the environment which the part must endure. A passive environment consists of daily temperature and humidity variations, occasional precipitation in the form of rain or snow, and ultraviolet radiation from sunlight. While care must be taken to account for the degradation or corrosion of materials in passive environments, more severe conditions require more robust designs. Often times engineers must design components to withstand damaging dust particles that cling to surfaces and retain moisture, or even chemically affect certain materials or coatings. Other corrosive environments may contain chemical vapors, high power winds, constant liquid submergence, an explosive atmosphere, or quite commonly (as seen aboard oceangoing vessels) salt fog. Material choices and design ideas must be based on the most severe anticipated service conditions as well as the required service life of the equipment.
While environmental conditions must be considered when producing a system that will be exposed to anything other than a constant non-corrosive atmosphere, engineers must also be careful to ensure that the physical characteristics of the item conform with required specifications. Even if corrosion resistance is of utmost importance, factors such as strength, size, weight, efficiency, performance, and cost must always be considered when a system is being designed. There is often no one single correct design for a component, therefore engineers are charged with the task of anticipating any and all conditions under which their product must function. The risks of improper design or material selection unfortunately often result in a multitude of problems, the worst of which may be complete failure. When the environment must be considered as a variable affecting product performance, an entirely different approach must be taken to ensure a design is effective.