Enclosures materials for water and wastewater facilities
26 May 2016
Harsh environments similar to those found in water and wastewater facilities can affect the ability of an electrical enclosure to protect the controls contained within, leading to a multitude of problems.
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Problems can include dangerous system collapses, production downtime, personal injury, and increased long-term maintenance costs and losses in customers. Consequently, it is critical for specifiers to become more knowledgeable about enclosure materials that prevent complications.
Even though many believe it should be easy to make a decision on the best enclosures material for an application, it can easily become overwhelming because all enclosure materials available will meet the immediate needs for most applications. However, in the majority of cases, there will be a specific material that is better suited for long-term reliability and overall cost reductions.
The most important factor to consider in material selection for protecting electrical components is the environmental characteristics of the application. Environments can be either indoors or outdoors, and depending on location, involves environmental factors such as moisture, ultraviolet radiation, dust, temperature, and other chemical and physical conditions at the site of permanent installation. An over-specified enclosure will work effectively in a natural environment, but an under-specified enclosure will eventually fail in a hostile environment, causing long-term consequences.
Water is the most common corrosive element and is usually present, to some extent, in every enclosure application. Adjacent processing operations or other intermittent activities such as industrial cleaning and the general plant environment may expose an enclosure to a variety of corrosive agents and temperatures. Each environment is unique and all possible corrosive agents should be identified for the intended enclosure application.
The level of corrosion typically increases with moisture content, especially in the water and wastewater environment. Common atmospheric sources of moisture are rain, dew and condensation. Rain can have a beneficial effect because it washes away contaminants from exposed surfaces. If rain collects in pockets or crevices however, it can be very detrimental because it supplies a source of continued moisture. When relative humidity exceeds 70 percent, a thin moisture film forms on a metal surface providing an electrolyte, this dew or condensation can become very corrosive if saturated with a contaminant like sea salt or acid compounds from industrial sources.
Materials available to protect electrical components in the water:
1. It can be made from metallic or non-metallic material, but must serve its function of protection for the life of the installation.
2. Durability and longevity is key.
3. There are two typical types of materials available: metal and plastics.
Common metal enclosure choices include carbon steel, stainless steel and aluminium. Carbon steel is the most prominent choice, based on its low initial cost. It is typically galvanised or painted to prolong the service life. Premium metals such as stainless steel and aluminium are used where long life, corrosion resistance and weather ability are critical, such as when one is protecting controls for junction boxes.
Thermoplastics, such as polycarbonate, polyester, ABS and PVC, offer a degree of corrosion protection beyond stainless steel in water/wastewater environments.
Composite fibreglass is not susceptible to rust or other forms of oxidation. Composite fibreglass enclosures also offer excellent chemical resistance to halogens (Chlorine, Fluorine) found in most water and wastewater facilities.
Polycarbonates are a group of thermoplastic polymers. They are easily worked, moulded, and thermoformed. Due to this versatility, polycarbonates are very widely used for enclosure applications.
Water/wastewater case study
Brian Murdick, a project manager at Morrow-Meadows Corporation, faced a challenge in which he needed an enclosure to protect electrical equipment at the Carlsbad Desalination Project on the coast of California.
Reverse osmosis is a process that makes desalination (removing salt from seawater) possible. According to Anees U. Malik and Ismail Andijani from the Saline Water Desalination Research Institute, "the RO (Reverse Osmosis) permeate is more corrosive than water produced by thermal distillation due to its high dissolved salts (TDS) level, particularly chlorides."
Due to the nature of the process, the RO environment is extremely corrosive. In addition to the process itself, the exposure to salt air due to the proximity of the RO plant to the Pacific Ocean heightened the risk of corrosion on the enclosure needed for this project.
During Brian Murdick’s search for a fibreglass option, a peer recommended Stahlin Non-Metallic Enclosures.
Stahlin's N Series Type 4X configurations are large control enclosures used in a variety of applications involving diverse environmental conditions. The Type 4X product is designed to meet the rigorous demands of indoor and outdoor applications. Control series enclosures are a natural choice for process control where moisture or chemical environments require unique protection, as they provide watertight, corrosion-resistant protection against a range of chemicals, windblown dust, rain, sleet and external ice formation.
Stahlin's N Series enclosures meet NEMA 250 Type 1, 3, 3R, 4X, and 12 standards. They can withstand a temperature range from -76 to 274°F, providing a UL94-5V flammability rating and the assurance of a NFPA No. 101: Flame Spread Class A (1).
Brian Murdick sums up his decision to use Stahlin products, stating that the Stahlin boxes were chosen because they are light weight, easy to handle and install, and will hold up better than stainless steel in this environment. Facing a challenge in a particularly corrosive environment, the Stahlin enclosure provides ample resistance against corrosion
Material selection is important for any product and has important implications for the performance that should be expected in water and wastewater environments. To make a proper selection, start by identifying environmental requirements of the application, and then narrow down your options to material types that fit the necessary requirements, size and ratings. Evaluate the thermal considerations the material will need to withstand, and the reactions of each material to such conditions. Finally, inspect and consider the initial and long-term costs and value of the materials that exhibit the best properties for the application, and choose the solution that has maximum value.
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