Choosing the Right Insulation Methods and Materials to Prevent Heat Loss

Extensive insulation repairs are usually done by contractors having the specific skills and equipment appropriate to the type of insulation being installed. Experience indicates that some insulation methods are much better than others, particularly for buried pipe.

Become familiar with the advantages and disadvantages of all the insulation methods before initiating the work. Refer to other references for an overview of insulation materials and insulation installation practices, and for the formulas needed to calculate heat loss. After selecting your general method of insulation, study the manufacturers’ literature. The following highlights deserve particular attention into insulation methods and insulation materials.

Moisture Resistance
No insulation system is able to keep moisture away from the insulation in the long term. The thermal resistance of insulation can be preserved entirely only by keeping it in a well drained enclosure. The enclosure may be the boiler house, a steam tunnel, or in the case of buried pipe, a drained conduit.

If it is impossible to keep the insulation dry at all times, as with buried pipe, the insulation itself should be impermeable to moisture. But, be aware that impermeable insulation alone cannot maintain thermal integrity or protect the pipe. Joints and cracks in the insulation allow water to travel between the insulation and the pipe, causing at least localized heat loss and corrosion. In this situation aiming in reducing heat loss is not achieved. No insulation material is entirely impermeable when exposed to continuous moisture.

Insulation Temperature Ratings
All new insulation should be rated for the highest temperature of the equipment being covered. This is true even if the insulation is being used to cover existing insulation, because a break in the original insulation can expose the new insulation to the temperature of the equipment.

With organic insulation, long-term exposure to heat reduces the strength of the insulation material. The rate of decay rises exponentially with temperature, so organic insulation should have a temperature rating that is substantially higher than the maximum operating temperature of the equipment.

Workmanship
Insulation should fit snugly all around the equipment. Also, adjacent sections of insulation should fight together tightly. Otherwise, heat is lost by convection between the heated surface and the insulation.

Using tape to cover gaps or hold insulation together is not satisfactory. All tape adhesives deteriorate with time, exposing any openings in the insulation.

Make the insulation removable at locations that may require access for maintenance, such as flanges, in-line traps, etc. Anticipate that water leakage may occur at such places, and install the insulation so that leakage at these points cannot soak the insulation. Leave an opening in the bottom of a removable segment of insulation to allow any water leakage to drain out.

Preformed Insulation
Preformed pipe insulation is a great labor saver. If it is sized properly, is provides snug contact with the pipe, reducing convection losses.

The elegant plant operator can now purchase custom fitted insulating covers for valves, steam traps, and other items.

Reflective Insulation
Reflective insulation is nothing more than a sheet metal shell surrounding a hot surface. It is a supplemental insulation method of reducing heat loss from localized surfaces of very high temperature, such as super heater elbows, where it would be awkward to use conventional insulation. The same metal shell may also be used as a safety guard. Reflective insulation is not appropriate as general insulation. Reflective insulation has little or no application in heating plants that operate at low and medium pressures. The metal covers sometimes seen on outside pipe systems are for protection against weather, and they do not function as reflective insulation.

Reflective insulation functions simply as a heat reflector. At very high temperatures, such as the temperature of high-pressure steam, radiation from a bare surface may account for much more calculate heat loss than convection. Heat radiation from hot surfaces is electromagnetic radiation in the infrared range, with a much longer wavelength than visible light. This radiation is reflected by a smooth metal surface. To function properly, the reflector must not touch the hot surface. The reflector should remain at low temperature so that it does not radiate heat.

The shell does not reflect perfectly, and the hot surface does not reabsorb all the reflected heat. As a result, heat radiation bounces back and forth between the pipe and the shell. The shell itself absorbs some of the radiated heat, becomes hot, and loses this heat to the environment. The efficiency of reflective insulation declines seriously as it becomes oxidized or dirty. Even at best, reducing heat loss from reflective insulation is much higher than with conventional insulation.

Don’t expect to enhance the performance of conventional insulation with reflecting insulation. The outer surface of the conventional insulation is so cool that it does not lose much heat by radiation.