An insulation system is the combination of insulations, finishes and application methods used to achieve specific design objectives.
Conditions exist in industrial installations, such as power plants, chemical plants, petroleum refineries, steel, pulp and paper mills, meat packing plants, food, soap and cosmetic process plants, and marine work, to name several, which require an insulation systems designer to be involved in the project during the design phase. Depending on the industrial process or function of the installation, these conditions include:
- stringent control of extreme temperature parameters.
- corrosive atmospheres resulting from the presence of process chemicals or the location of equipment and piping outdoors.
- increased fire hazard caused by high temperatures and the presence of volatile substances.
- presence of operating personnel (personnel protection).
- sanitary and contamination requirements for food, meat packing, soap, cosmetic, dairy and brewery processes.
- additional mechanical abuse to insulations from excessive handling, foot traffic on vessel tops and lines, and the added movement of expansion, contraction and vibration.
- necessity for easy removal of insulation for predictable maintenance areas.
- critical clearance and space limitations coupled with the need for greater thickness of insulations.
- complex construction and installation schedules.
- radiation hazards in nuclear facilities.
- work accessibility requiring scaffolding, cranes and other items.
Pertinent data concerning the installation design objectives, the materials being processed or used, applicable government regulations or codes, operating data and temperature parameters must be determined far enough in advance of final specification preparation to insure the design of a properly functioning insulation system.
Nature of the Process
The possibility of spillage, leaks and accidental contamination of process chemicals and products is always present in industrial installations. Insulations should be chosen which don’t react to the chemicals contained in the vessels or piping to which they’re applied. Such a reaction may lower the ignition temperature of the process chemical or insulation material, contributing to fire hazard conditions.
Special care should be taken to use non-absorbent insulation in the presence of combustible or toxic liquids. Spontaneous combustion of a combustible liquid absorbed over the large surface area of insulation may occur as it oxidizes. Absorbent insulation may contribute significantly to an accidental fire by storing up the spilled or leaked combustible materials.
United States Department of Agriculture (USDA) standards for food, soap and cosmetic manufacturing plants prohibit use of insulations which sliver or dust, are toxic, or contain glass. Equipment, piping and insulation must be provided with finishes which will not support fungus, mildew or bacteria growth. The finish must resist washing down with high-pressure water, steam and detergents without appreciable deterioration.
In meeting USDA requirements, plastic laminates and finishes excel in their resistance to fungal and bacterial growth although their temperature and mechanical strength limitations pose problems in high pressure wash down areas and under long periods of steam cleaning.
Stainless steel is the most appropriate of the metal jacketing materials, having high resistance to corrosives and bacterial growth as well as high mechanical strength. Aluminum may erode in wash down areas or where strong cleaning chemicals are used. The use of weather and vapor retarder coatings, reinforced with glass cloth or mesh, provides a mechanically strong and sanitary finish for equipment and other irregular surfaces. Many are also resistant to chemicals.
Temperature Parameters of Piping and Equipment
In addition to the reduction of heat loss or gain, industrial insulation systems must maintain controlled temperatures required for process materials being transported from one point in a facility to another. Temperature control may be continuous, intermittent, cyclic or rapidly changed due to weather conditions or the necessity of steam cleaning and wash down periods.
An insulation of high thermal diffusivity, low specific heat and low density is desirable in installations which require rapid heat-up or cool-off of insulated surfaces. A process changing from hot to cold every few minutes requires an insulation that has the ability to change temperature quickly and has very low mass to retain heat.
The temperature of an insulation’s outer surface must be considered where insulation is used for personnel protection or where excessive surface temperatures might cause ignition of fumes or gases. On low temperature installations, surface temperatures must be above dewpoint to prevent condensation and drip. The emissivity property of insulation finishes is significant in these cases. High emissivity is recommended on finishes used for personnel protection treatments.
On installations where temperatures must be maintained at specific levels, it must be decided in the design phase whether added insulation thickness or heat tracing would provide the most efficient service. This decision is based on data other than the conventional economic thickness considerations.
Extreme temperature surfaces in industrial process and power facilities may require the use of materials and application methods which can absorb expansion, contraction and vibration movement. Stainless steel banding or expansion bands are recommended for applications with extreme expansion movement or on large diameter surfaces. Because most high temperature insulations shrink while the metal surface expands, methods such as double layer-staggered joint construction, the design and placement of cushioned expansion joints and/or the use of high rib lath between insulation and metal surfaces may be employed to protect the insulation seal.
Awareness of the nature of the process, its components, the relative temperatures of piping and equipment and the general location of such equipment and substances, aids the specifier in determining areas where excess heat or chemistry may create fire hazards or personnel hazards.
Metal Surfaces Receiving Insulation Treatment
A selected insulation shouldn’t be chemically reactive to the metal over which it’s applied. Basically, insulation installed on steel should be neutral or slightly alkaline. That installed on aluminum should be neutral or slightly acidic.
External stress corrosion cracking of stainless steel may result from the presence of chloride ions on its surface. Insulation containing chlorides or located on a salt-laden or chloride contaminated atmosphere must not be in direct contact with unprotected stainless steel jacketing or surfaces. In the case of stainless steel jacketing, factory-applied moisture barriers on the inner surface may be sufficient protection.
Insulation systems must be designed to prevent possible galvanic cell corrosion to metal piping and equipment. Some industrial, high temperature insulation materials contain salts which, when moist, set up a low voltage galvanic cell with the iron pipe or vessel wall as the positive pole and metal jacketing as the negative pole. This action results in either the pipe/vessel wall or the jacket, sacrificing itself to the point of failure. Humidity levels, temperatures and salt content must be considered when specifying insulation materials, mastics, jacketing and accessories.
The location of instruments and maintenance areas where personnel will be present is significant when specifying treatments for personnel protection and materials abuse protection from foot traffic, excessive handling and operational machinery. Rigid insulation materials and jacketing are recommended in these areas. High-pressure wash down areas require resistance to water and detergents along with high mechanical strength.
Future Access and Maintenance Requirements
Leaks are most likely to occur at valves, fittings and flanges. Low temperature insulation can be protected from leaks by sealing off adjacent insulation with vapor-retarder mastics. Removable fitting covers may be specified at predictable maintenance areas, while special leak detection mechanisms may be installed at other locations. However, on hot applications a rigid inspection and replacement program is the best prevention of large scale insulation destruction due to leakage.
Turbines, which require easy access for inspection and maintenance, can be insulated with removable insulation blankets fabricated from stainless steel mesh or high temperature fabric filled with fibrous insulation. These are attached to turbine surfaces by means of metal eyelets built into the blankets around the edges.
The floor level of large tanks can be protected from spilled chemical or water from wash downs by using a nonabsorbent insulation along the bottom skirt or support, or by sealing with caulking.
The atmosphere surrounding industrial piping and equipment presents additional problems in the selection of finishes and jacketing. Of particular concern is the presence of chemicals or humidity which act to corrode metal finishes.
Because of its excellent weather-barrier and mechanical properties, metal jacketing is widely used on industrial installations. The metals most resistant to corrosive chemicals and humidity are stainless steel and coated electro-galvanized steel. Coated aluminum can be used to combat specific conditions by selection of the exact coating required. However, the coatings aren’t always abrasive resistant, leaving the aluminum open to attack at fastener openings and cuts.
Aluminum is weather resistant but doesn’t always hold up in wash down areas or where strong cleaning chemicals are used. Factory-applied moisture barriers are recommended on aluminum jacketing.
The coverings considered most resistant to corrosives and abrasive chemicals are the plastic types. Unless protected, some PVC type coverings may break down when subjected to the effects of ozone, infra-red or ultra-violet rays. Protective paints are available for PVC coverings not manufactured for outdoor use. Weather barrier coatings offer good protection from weather as well as from the chemical attack of acids, alkalies, solvents and salts, either airborne or as a result of intermittent spillage. Glass cloth and other fabric membranes are generally used as reinforcements and add mechanical strength to the insulation.
Maximum protection from chemical attack on cold and dual temperature service is achieved through the use of vapor retarder coatings. They, too, are applied with reinforcing fabric.
Stainless steel jackets and bands are recommended in areas which require superior fire resistance. Stainless steel is recommended over the use of aluminum due to the latter’s lower melting point. Some weather and vapor-retarder mastics also offer fire retardant properties to an insulation system.
Because of the complexity of process piping and the added thickness required to control heat loss or gain, clearances often become so minimal that it may be necessary to insulate piping together in groups. This is also true in marine work.
Scheduling and Materials Storage
Precise industrial installation schedules and good application practice often dictate that insulation be finished as soon as possible after roughing in. The chosen materials must have the necessary strength to resist and excessive amount of handling and moving at the installation site. Materials which are moisture absorbent must be protected from water while being stored at the site. Storage areas should be clearly indicated for the insulation contractor in project specifications, and should be noted as covered or open.
Contract drawings should indicate the extent and general arrangement of the site and the process piping to receive insulation treatment. The size of piping and equipment, line origination and termination, elevations, support locations, and orientation of nozzles, fittings and valves should also be indicated and properly dimensioned.
Quality of Materials
Insulation and associated materials should be specified and ordered to meet appropriate codes and standards. Manufacturers’ data sheets and test reports should be consulted in the selection process to determine conformity.
Adapted from Section III (Insulation Systems Design) of the National Commercial & Industrial Insulation Standards, published by the Midwest Insulation Contractors Association.