Preventing Moisture Intrusion among Insulation System
Article Source: HealthSnare.com
The CUI or corrosion under insulation is the decay of piping and vessels that happens when there is diffusion of water. The water usually came from leakage, deluge water system, rainstorm, and wash water or even from sweating from temperature cycling or low temperature process such as in refrigeration units.
This corrosion is hidden underneath the insulation and may remain undetected until removal and inspection is done or when actual occurrence of leak is noticed. CUI had been and still a growing concern in many industries such as refineries, power plants, petrochemical or industries based onshore or offshore.
The two main ingredients of CUI are moisture and warm temperatures. Oxygen is necessary for iron products like carbon steel piping and equipment. For stainless steel under 300 series, chloride ions are needed to have SCC or stress corrosion cracking.
One of the ever available and most abundant elements is oxygen. Maybe surprisingly, chloride ions too are plenty. Sources of it are rain water, sea water, drinking water, and chemical compounds of chloride turn that these liquids into salt. Acids, strong bases, salts and acid gases can create and make corrosion grow fast.
Generally, there are various ways for the many forms of moisture to get inside the insulation system. Rain is the most common method, but insulation systems which are located in the low-lying regions can be flooded by water that comes from pressurized sources or even steam leaks. Water from fire protections sprinkler systems is almost the same as a rainstorm.
Then the cause of moisture is the water vapor going and soaking into the insulation systems operating under ambient temperatures, as the final source, is operated below freezing point. Insulated equipment and piping under layers of ice escape corrosion as the low temperature prevents oxygen and heat. Ice as the final source usually, the cold service insulation systems are used lesser the freezing point. Insulated equipment and piping under layers of ice escape corrosion as the low temperature prevents oxygen and heat, as the ice freeze and thaw continuously it creates an area which is almost perfect for corrosion.
In fact, the optimum range of temperature to achieve an aggressive corrosion on carbon and stainless steel is at about 200 F to 240 F. In this series, the presence of heat energy is abundant but still its not enough to evaporate the moisture by hitting the surface of the equipment.
Water vapor can penetrate and soak the insulation systems by operating at ambient temperatures. Ice, as a final source, normally operates on or below freezing point. Insulated piping or equipment under layers of ice escapes corrosion due to limited supply of oxygen and heat. But as the ice freeze and thaw continually, a near perfect corrosion area is provided.
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Debbie Stevens
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Date: Mon, 3 Jan 2011 Time: 2:48 AM
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