Don’t consider insulation a ‘cost’! When properly done, the insulation of your facility doesn’t add cost to the product the facility produces. It saves operating expenses, thus allowing the owner/manufacturer to become more competitive in the market. An insulation system can actually pay itself back and then continue to earn savings of energy during operation. This can be translated directly to increased efficiencies in the plant, a lowering of expenses, and potentially an increase in market share with a gain on profits earned.
Since the beginning of time, insulation in one form or another has been a part of everyone’s 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; thus becoming a very important part of all construction projects. Yet, we often see insulation as 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. The emergence of new and improved insulation materials and products to protect the insulation is something that our entire industry strives toward. It is something for which we all can be proud. 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 have all become more involved with the selection of materials for a specific project. We 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 very important to the efficient operating of an insulation system.
The term "high temperature market" means different things to different people. You may be surprised to find that 80 percent to 90 percent of the above ambient operating systems, whether commercial or industrial, operate at 300 degrees Fahrenheit (F) or below. And it may be of interest to note that for example, only about 20 percent of the piping in a power plant may exceed 350 degrees F. For the purpose of this article, let’s assume that high temperature can refer to pipe operating temperatures to 450 degrees F. Above 450 degrees, 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 450 degrees F is steam and process piping. These are primarily found in the industrial market, such as chemical, petrochemical, pharmaceutical, power and refining.
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 good to 450 degrees F, or above. Preformed or fabricated, these insulation materials are readily available. But what other factors should be considered for hot applications today?
System Design-Avoidable Mistakes
It 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.
As an industry it’s critical that we promote involvement with owners and their engineering and design firms at the very beginning of the 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 we run into obstacles in the field that end up jeopardizing the insulator’s ability to properly insulate the system. What job sites have you walked through and found the following:
- Pipes that aren’t spaced far enough apart and don’t 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 don’t 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 with the owner by the engineer to the general to the mechanical is imperative.
Involvement that includes the insulation contractor may facilitate proper installation.
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 performance of the insulation may be extremely costly to the owner because the process was compromised.
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’s important to take time and review the material and jacket systems that are being chosen for a project. Whether it’s an engineer starting to design a project, an end user trying to determine what he wants or a salesperson trying to sell an insulation material, the technical information should be reviewed thoroughly.
Each manufacturer publishes test data for the product it makes. They typically list physical properties such as thermal conductivity, compressive strength, density, temperature range and flame and smoke development. 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’s quite an undertaking and almost impossible to directly compare all the materials listed earlier.
The testing organization ASTM had the daunting task of developing methods to test materials. As each of the materials are so different in composition, i.e., some fibrous, some rigid, some cellular, etc., in many instances, ASTM had to develop completely different tests, or different methods within a given test, for the same physical property because of differences between 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 a different test method to measure a fibrous material, a different method for a cellular glass, cal-sil, etc. Each product has a compressive strength, however, none of the materials can be judged by one encompassing test.
Many ASTM tests contain several methods of testing 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’s 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, people 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 over the years as plants continue to improve all safety aspects of their facility. Many products with a 25/50 rating at 1 inch thick doesn’t meet the 25/50 rating at a greater thickness, as in two layers of 1 inch each on a pipe. It’s important to network with the manufacturer regarding your materials of choice to identify the flame and smoke rating for the specified thickness of insulation required of the project.
Calculating thickness for a specified heat loss or surface temperature requires comparison of thermal conductivity of the insulation. Most ASTM test methods are based on an oven -dried sample tested at 75ºF mean temperature. What is important to know when designing the system, is the K Factor at the ‘operating’ temperature. It will be different than the published value.
In addition, it’s important to find out what happens to the insulation product at the elevated operating temperature for all of its physical properties. There are two ASTM tests that measure a host of physical characteristics of the product, 1) while in-service at higher temperatures and 2) 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. It’s interesting to note that most insulation materials perform differently compared to their data sheets, all properties at 75 degrees F mean, when compared to system operating temperatures. This isn’t a bad thing. These tests are only provided to increase awareness. During the design phase, identifying and addressing potential problems, such as shrinkage or warping, allows the engineer to build safety factors into the system such as double layer applications and expansion/contraction joints to provide a system that’s not doomed from the start.
Couple the differences of testing and test methods with the fact that manufacturers don’t 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 effects the application as well as how it changes when applied to the temperature of the system being insulated.
Fabrication of High Temperature Materials
Fabrication plays an important role in application and function of an insulation system. From the proper fabrication of elbows, flanges, valves and pipe supports, to the manufacture of insulation for large diameter pipe or small vessels. Attention to proper miter spacing ensures a proper fit in the system; both in closure around the pipe and/or fittings inside of metal covers.
Careful attention must be taken to all details of the fabrication process, including that of meeting exacting tolerances, in order to maintain the integrity if the insulation. Once again adhesives that glue the materials together are very important. Compatibility with the insulation as well as attention to flammability with the system must be considered.
For example, cellular glass is often 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 their own limitations. The cement shouldn’t be used on a cold system unless liquid nitrogen, and the asphalt can soften at 250 to 300+ ºF. If asphalt is used to adhere insulation miter sections together to make a fitting for a system that’s operating at 450ºF or above, the system will fail because the operating temperature is too hot and will cause the asphalt to melt. At the higher temperatures, the gypsum cement should be applied.
Another consideration when fabricating fittings of fibrous glass is the adhesives used to glue mitered fittings. The end service temperature isn’t always known. Adhesives that work well at lower temperatures aren’t advised at higher service temperatures. If the adhesives aren’t suited to the operating temperature, a flashing of the adhesive may occur; expelling smoke to the atmosphere and/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 provides another location for water ingress.
Altering the insulation structure can have important implications. Most fibrous pipe insulation fibers wrap the pipe, i.e., 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.
Just as important as the insulation choice is to the project, the use of accessory items is to the insulation. Everything must align and mesh together to perform properly. Coatings, adhesive sealants, and claddings all must be compatible with each other and the operating conditions of the system. 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 can be considered. This must be coupled with the expansion of the pipe/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.
Final Design Considerations
As the No. 1 enemy of any insulation system, whether hot or cold, is water; all choices for the system must be reviewed to make sure that the system is breathable, yet water-tight. Additional lines of defense against water should be incorporated into the total design.
It’s a misnomer that water can’t 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, at fittings, flanges, valves and other areas. As we are discussing high temperature lines of pipe to 450 degrees F you may note that through the thickness of the insulation, heat is dissipated to the surface of the insulation. To meet minimum surface temperatures of personnel protection; approximately 110 degrees F, the thickness of insulation will experience a temperature gradient from 450ºF to 212ºF, which is below that of steam, to 110ºF at the surface. The thickness of insulation that can be identified from 212ºF to 110ºF at the surface, is where water can be retained in the insulation.
Left in operation, yes, this portion can be dried, but at what expense? With the next rain, water will enter the system. The resulting expense isn’t 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. The surface temperature may now exceed what is safe for personnel. And, as systems are continually 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 large destroyer of the expensive piping substrate and a huge expense to the owner. Continual maintenance is essential and a proper piping primer for the operation temperature applied to the pipe will help increase the service life of the pipe.
Insulation is the only expenditure that the owner incurs that actually earns him a payback. When reviewing and comparing potential installation choices, the lowest price at installation isn’t always the most economic choice. Adequate insulation thickness, such as design for a minimal heat loss as opposed to design for thickness that will protect personnel (i.e. usually less thickness), can reap the owner instant rewards as well as continual rewards over the life of the installation. Most insulation manufacturers are able to provide an energy analysis and a return on the owners investment in insulation 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 the owners about the benefits of a system that can help them be more competitive in their marketplace. We all share in the responsibility of working together throughout the entire insulation process. It’s the expertise and the experience of everyone in the industry that can help insure that the insulation system(s) can be properly designed, installed and maintained.