Since the beginning of time, insulation in one form or another has been a part of our lives. The basic idea of keeping something hot or cold has evolved into the need to conserve energy, protect personnel, reduce operating costs and reduce emissions. Yet, insulation is often one of the project line items where corners are cut.
Trying to digest all of the milestones that the insulation industry has reached is quite a task. New and improved insulation materials have emerged. When so many materials meet the majority of the criteria of consideration for installation, the difficult task is determining not what type of insulation could be used but what type of insulation should be used in a specific application. With rising energy costs and the need to reduce energy and emissions, a properly insulated system has never been more important.
How can this be done correctly? Insulation manufacturers, fabricators, contractors and distributors all have become more involved with the selection of materials for a specific project. They have the responsibility to assist in helping make the correct choices in all aspects of the insulation selection and application process. Being involved means being accountable. It means becoming aware and understanding a lot of hidden details that are sometimes not so obvious but are important to the efficient operation of an insulation system.
System Design: Avoidable MistakesIt sometimes seems that insulation is an afterthought. Contributing factors to this may be because the insulator is one of the last trades on the project, or that on a new construction project, the line item cost associated with the insulation system is a small part of the total project.
The insulation industry says it is critical that it promotes involvement with owners and their engineering and design firms at the beginning of the design/build process if the insulation system is to function properly. Before an insulation material and jacketing system can be chosen, many parameters must be considered. Common problems associated with failed insulation could be avoided if the substrate could be designed to allow for the proper insulation application.
Too often, there are obstacles in the field that jeopardize the insulator's ability to properly insulate the system. Common problems that insulators find include:
- Pipes that are not spaced far enough apart and do not allow for the correct insulation thickness to be installed, nor enough room to work and provide a good installation of the insulation.
- Flanges, valves, elbows and other items installed too close together, making it impossible to properly insulate.
- The use of valves that do not have extended bonnets on them to allow for the correct insulation thickness under the valve handle or allow for maintenance of the valve.
- I-beams, braces, brackets and other items coming in contact with the pipe, causing a thermal short.
- Gauges, pipes and man-way doors installed too close to the vessel or equipment, making it impossible to insulate around or above.
- Improper type of pipe support used.
- Pipes not primed before insulation is installed because it was never specified.
Are these items pipe system design problems, pipe installation problems or a combination? The reality of most construction projects is that while the best (or worst) of design and drawings may be provided to the general -- and thus to the mechanical -- contractor, many projects require changes in the field. This is where good communication among the owner, engineer, general contractor and mechanical contractor is imperative. Including the insulation contractor in these discussions may further facilitate proper installation.
Material SelectionThe term “high temperature market” means different things to different people. Eighty percent to 90 percent of the above-ambient operating systems operate at 300oF (149oC) or below, and only about 20 percent of the piping in a power plant may exceed 350oF (177oC). For the purpose of this article, assume that high temperature refers to pipe operating temperatures to 450oF (204oC). Above 450oF, many different considerations must be examined that will not be part of this article. The most common pipe operating in the above-ambient range to 450oF is steam and process piping -- primarily found in chemical, petrochemical, pharmaceutical, power and refining markets.
Fiberglass, mineral wool, calcium silicate, ceramic fiber, perlite, cellular glass, removable covers and, more recently, high temperature polyisocyanurate all state that their maximum operating temperatures are 450oF or above. Preformed or fabricated, these insulation materials are readily available. But what other factors should be considered for hot applications today?
Criteria for selecting insulation material should include the reason for insulating. In the high temperature market, the primary reason for insulating a process line is process control. Insulation may be extremely critical to the process. For example, some processes may only allow for a minimal temperature fluctuation. Erratic insulation performance can compromise the process -- which can be extremely costly to the processor. Most other piping is insulated to protect personnel or to provide an acceptable heat loss.
Once the lines to be insulated have been determined and the ultimate goal of the insulation installation is understood, it is important to take time and review the material and jacket systems that are being chosen for a project.
Each manufacturer publishes test data for the products it makes. Physical properties such as thermal conductivity, compressive strength, density, temperature range and flame and smoke development typically are listed. Each characteristic has a direct bearing on the insulation product's ability to perform properly during operation of a given process or application at its service temperature. It is quite an undertaking and almost impossible to directly compare all the materials listed earlier.
The testing organization ASTM International, originally known as the American Society for Testing and Materials (ASTM), had the daunting task of developing methods to test materials. As each of the materials are so different in composition (that is, some fibrous, some rigid, some cellular, etc.), in many instances, ASTM had to develop different tests, or different methods within a given test, for the same physical property because of differences among types of materials. The following are several examples of which you may or may not be aware.
In the instance of identifying the actual compressive strength characteristic of a product, ASTM has different test methods to measure fibrous materials, cellular glass, calcium silicate pipe insulation, etc. Each product has a compressive strength; however, none of the materials can be judged by one encompassing test.
Many ASTM tests contain several testing methods within the test for a specific physical characteristic. In the example of water absorption, there are six methods within, all identified by one main test number. It is of interest to note that one product sample, cut into six pieces and exposed to each six test methods, will not yield the same result.
In the past, those involved with industrial applications have not been as concerned as those involved with commercial installations in regard to the flame and smoke rating of a product. However, this has been changing as plants continue to improve all safety aspects of their facilities. Many products with a 25/50 flame spread/smoke development (FS/SD) rating at 1" thick do not meet the 25/50 FS/SD rating at a greater thickness, as in two layers of 1" each on a pipe. It is important to consult with the insulation manufacturer regarding your choice of materials to identify the flame and smoke ratings for the specified insulation thickness required for your project.
To calculate the required thickness to achieve a specified heat loss or surface temperature requires comparing thermal conductivity characteristics. Most ASTM test methods are based on an oven-dried sample tested at 75oF (24oC) mean temperature. When designing the system, it is important to know the K factor at the “operating” temperature. It will be different than the published value.
It also is important to find out what happens to the insulation product at the elevated operating temperature for all of its physical properties. Two ASTM tests measure a host of physical characteristics of the product while in-service at higher temperatures and after it has been in-service for a specified length of time. These two tests identify the insulation's ability to perform at in-service temperatures.
Most insulation materials perform differently compared to their data sheets (all properties at 75oF mean) when compared to system operating temperatures. This isn't a bad thing. These tests only are provided to increase awareness. During the design phase, identifying and addressing potential problems such as shrinkage or warping allow the engineer to build safety factors into the system.
Couple the differences of testing and test methods with the fact that manufacturers do not have a standard listing of test results to report on their data sheets, and one realizes that real comparison requires a good understanding of products and testing methods and the ability to read between the lines. Analyze how all of this information affects the application as well as how it changes when applied to the temperature of the system being insulated.
Fabrication of High Temperature MaterialsFrom the proper fabrication of elbows, flanges, valves and pipe supports, to the manufacture of insulation for large diameter pipe or small vessels, fabrication plays an important role in the application and function of an insulation system. Attention to proper miter spacing ensures a proper fit in the system in closure around the pipe or fittings inside of metal covers.
Careful attention must be paid to all details of the fabrication process, including that of meeting exacting tolerances, in order to maintain insulation integrity. The adhesives used to glue the materials together are important. Compatibility with the insulation as well as attention to flammability with the system must be considered.
For example, cellular glass often is glued together to make fittings, valve covers and other components. There are two basic means to adhere the cellular glass sections together: hot asphalt or gypsum cement. Both products have limitations. The cement should not be used on a cold system unless it is liquid nitrogen, and the asphalt can soften at 250 to 300oF (121 to 149oC). If asphalt is used to adhere insulation miter sections together to make a fitting for a system that is operating at 450oF or above, the system will fail because the operating temperature is too hot. At higher temperatures, gypsum cement should be applied.
The end service temperature is not always known. Adhesives that work well at lower temperatures are not advised at higher service temperatures. If the adhesives are not suited to the operating temperature, a flashing of the adhesive may occur, expelling smoke to the atmosphere or, subsequently, the glue evaporates and the insulation falls away from the pipe. This provides another thermal short in the system, increasing energy expense and usually providing another location for water ingress.
Altering the insulation structure can have important implications. Most fibrous pipe insulation fibers wrap the pipe; that is, the insulation runs parallel to the pipe or substrate. These parallel fibers create air gaps that improve the insulation's thermal properties. If the fibers are cut and then installed perpendicular to the pipe, it will not function as efficiently, as there is now a flow of air directly away from the pipe.
Compatible Components.Just as important as the insulation choice is the choice of accessory items. Coatings, adhesive sealants and claddings all must be compatible with each other and the system operating conditions. They must be able to hold up to the same conditions as the insulation. Each one should be reviewed and carefully assessed. If one of them fails to perform properly, it will jeopardize the integrity of the total installation.
While this is an article on insulation materials in high temperature service, not only insulation and cladding should be considered. The choice of insulation materials must be coupled with the expansion of the pipe or vessel at the service temperature. Coefficients of expansion or contraction of the insulation material at the service temperature must be known. Most insulation products will shrink with heat while the pipe expands with heat. Properly installed expansion/contraction joints and supports are a must. In addition, double-layer insulation can help alleviate bare or hot spots between insulation sections.
Expel Enemy No. 1The No. 1 enemy of any insulation system, whether hot or cold, is water. All choices for the system must be reviewed to ensure that the system is breathable yet watertight. Additional lines of defense against water should be incorporated into the total design.
A common misbelief is that water cannot be found in the insulation of a hot service line. Water ingress can be noted under improperly installed or maintained jacket laps, improper spacing of jacket ends and at fittings, flanges, valves and other areas. On high temperature (450oF and above) pipe lines, heat is dissipated through the thickness of the insulation to the surface. To meet minimum surface temperatures for personnel protection (approximately 110oF [43oC]), the thickness of insulation will experience a temperature gradient from 450 down to 212oF (100oC), which is below that of steam, to 110oF at the surface. The thickness of insulation that is between 212oF and 110oF is where water can be retained in the insulation.
Left in operation, this portion can be dried, but at what expense? If the piping is outdoors, with the next rain, water will enter the system. The resulting expense is not only an increase in energy required to dry the system but the added danger of a raised surface temperature. Remember, water is a conductor, not an insulator. Wet insulation may cause the surface temperature to exceed what is safe for personnel. And as systems are taken out of service for maintenance, impurities from the atmosphere will travel via water through the insulation to the pipe surface, layering salt and other corrosive elements under the insulation. Corrosion under insulation is a hidden and significant destroyer of the expensive piping substrate and a huge expense to the processor. Continual maintenance is essential. In addition, applying the proper piping primer to the pipe for the operating temperature will help increase the pipe's service life.
Positive PaybackWhen reviewing and comparing potential installation choices, the lowest price at installation is not always the most economic choice. Adequate insulation thickness, such as that designed for minimal heat loss rather than designed for the thickness that will protect personnel, can reap the processor instant and continual rewards over the life of the installation. Most insulation manufacturers are able to provide an energy analysis and a return on investment analysis based on the design criteria and current energy costs.
The key is coordination. Insulation manufacturers, fabricators, distributors, insulation contractors, mechanical contractors and designers/engineers must educate you, and you must educate yourself, about the benefits of a system that can help you be more competitive in the marketplace. Each shares in the responsibility of working together throughout the entire insulation process.
This article originally appeared in the November 2003 issue of Insulation Outlook,published by the National Insulation Association, Alexandria, Va., www.insulation.org. Edited and reprinted with permission.
Report Abusive Comment