Pipe Insulation Support Saddles
Thermal piping systems require mechanical support in nearly every application, the lone exception being direct burial piping applications. In almost all other applications, a hanger or other support device is required to secure the pipe at its point of attachment to the structure that the piping is crossing or servicing. The methods used to support thermal piping all seek to provide structural rigidity to the system. Whether or not this comes at the expense of thermal efficiency is a critical difference between the methods. We will examine some of the more common ways of dealing with the issue of support and thermal efficiency at clevis hangers and roller support locations in thermal piping systems.
Traditional Support Methods
Insulated piping installed in clevis hangers in commercial applications is generally supported by a pipe insulation protection shield (also known as saddles) of dimensions sufficient to keep the insulation from being crushed in the support area. Originally slightly more than a half- cylinder of sheet metal (see figure 1), these shields remain largely unchanged with a few notable exceptions from certain manufacturers.
The shield’s function is to distribute the load forces created by the loaded pipe (plus valves, flanges, strainers or other items) and the insulation that exists between support locations over a larger insulated surface area than would be present in the bare clevis hanger without a type 40 shield. The support spans are usually governed by project specifications (or Manufacturers Standardization Society Standard Practice [MSS SP-69, table 3 or table 5]). MSS SP-69 states accepted maximum spans for assemblies using certain types of hangers, with spans as short as 6 feet for small bore pipe, and as long as 20 feet for large bore pipe. Spans are often determined by the location and availability of structural members to hang or attach a support. Because of this, they can vary from the numbers in MSS SP-69 table 3 or 5 by a considerable margin.
In theory, the dimensions of type 40 shields or saddles are controlled by the MSS SP 58, Table 5, for type 40 shields. MSS SP-58 is based upon protection of insulation having a compressive strength of 15 psi, which is a higher compressive strength than that of many common insulation materials. Insulation types such as low density fiberglass and most elastomeric foams are "softer" than 15 psi.
The length and gauge of the shield (saddle) is determined by pipe size, not by insulated outer diameter (see figure 1.1). To compensate for an insufficient shield length and insulation compressive strength, the insulation materials will often receive inserts such as support plugs or blocks, constructed of a high-density material such as wood. These plugs and blocks become the load-bearing components of most field-fabricated saddle assemblies for cold applications. They do possess good load-bearing properties, but these items aren’t efficient insulation materials. They create a compromise between compressive strength and thermal performance. In reality, the requirements for most projects fall short of the dimensional standards shown in MSS SP-58, table 5. They’re viewed by many as being in excess of what’s actually necessary to provide proper performance. Typically, only U.S. Army Corps of Engineers projects have strict standards resembling the dimensions of MSS SP-58 table 5.
Treatment of Piping
Insulated piping installed on roller hangers or supports require a different treatment. It typically receives a heavy duty weld-on shoe-type support saddle (MSS SP-58 type 39 or Grinnell figure 164 – figure 166) to prevent crushing of the insulation in the roller contact area. (Grinnell [now Anvill] product "figures" are commonly used in project drawings as detail items for clarification purposes. They are common call-outs for mechanical contractors.) The insulation is generally butted against this steel support and carefully worked around the legs to the greatest extent possible (see figure 2). The metal-to-metal contact in the support area causes poor thermal performance and is impossible to seal completely. It has undeniable structural superiority, but this comes at the expense of thermal performance and condensation control.
Unchecked condensation will drip to surfaces below the support, lead to corrosion of the metallic support components and ultimately contribute to premature component failure. Even when material specifications call for wooden support saddles (Grinnell Figure 179 wood insulation saddle) on chilled water lines, the thermal conductivity and condensation issues need to be addressed. Wood and steel are fine building materials for structural purposes, but they offer less than reasonable insulation value and thermal performance. They seem to be inherited from one project specification to the next, allowing the problem to continue.
The metallic support items (type 40 shields and type 39 saddles) described so far are versatile and non-specific as to temperature range. They’re widely accepted for both hot and cold applications. They leave the issue of insulation performance more to the installer, instead of the designer or specifier. Some may argue that the total amount of piping subject to poor insulation performance from traditional hanger treatments is insignificant. This isn’t a valid argument if we’re dealing with a cold system. A small area subject to water vapor penetration will cause a large problem if left unchecked. The best way to treat this problem is through a proactive materials selection process. By being proactive, you can solve the problem with preventive action.
A basic division of intended applications should occur at this point: Is the application hot or cold? Cold applications receive far more attention than do hot because of the obvious condensation control issues on cold piping, versus visually undetectable heat loss issues on hot piping. A simple high-density mass insulation insert (calcium silicate or perlite) in the support area is sufficient for most hot piping applications. Heat loss in hot piping systems can have notable economic impact and create personnel protection liability, but it still doesn’t attract the attention that heat gain receives in cold piping systems.
The Role of Insulation Compressive Strength
The higher the compressive strength of the insulation, the shorter the support saddle has to be to carry a particular load. A saddle supporting 50 psi compressive strength foam insulation in a clevis hanger can be shorter in length than a saddle supporting 24 psi compressive strength foam insulation. How much shorter depends on two factors; the specified support span (per MSS SP-69 and American Society for Testing and Materials [ASTM B31.1]) and the resulting load for the support (span load). The span load is determined by the total weight of the pipe, filled with water, covered with insulation and metal jacketing, per linear foot, multiplied by the footage between supports. Additional loads such as valves and flanges must be added to the span load calculation. Of course, smaller diameter pipes have lighter span loads than do larger diameter pipes. Safety factors can be applied here as well, such as using schedule 80 pipe and 3 inch thick 14# pound per ft3 PCF density insulation for all calculations. This is the baseline load number for the span.
The maximum load per type 40 saddle is based on the length of the saddle in inches, multiplied by the compressive strength of the insulation in psi, times one-third of the insulated outer circumference. This is usually a much greater value than the span load. The percentage difference between the maximum load per saddle and the pan load is called a safety factor. Individual project requirements vary widely, so no widely adopted uniform standard for insulation support saddles exists. There have been numerous field expedients applied over the years, and many of these have evolved into products developed out of requests from the field.
The previously mentioned calculations are necessary to perform if correct support is critical. However, they can be left to those who manufacture insulated saddles and design each saddle for a particular application and load range.
Modern Alternative Support Methods: Starting a Proactive Program
Manufactured insulated saddles (also called pre-insulated saddles or insulated pipe supports) are offered in response to the needs of designers, owners and installers seeking a better way to treat the challenging conditions which exist at the pipe hangers and supports within any thermal system. Traditional thermal insulation systems for piping have concentrated primarily on straight runs of piping. Numerous thermal leaks were left at hanger and support locations because of a lack of well-designed products to use at these locations. Trade-offs between compressive strength and thermal performance in the saddle area are common with field-insulated saddles, but are eliminated with manufactured insulated saddles.
With a variety of insulation types ideally suited for conditions within a particular temperature range, insulated saddles offer the correct insulation for each application. Insulations for most cold applications are 3# minimum density rigid polyisocyanurate (cellular glass can also cover this temperature range, but it lacks significant compressive strength) for the wide range of temperatures between minus 100 degrees Fahrenheit (F) and 250 degrees (F). High strength calcium silicate and perlite are typically best for high-temperature applications from 250 degrees (F) through 1,200 degrees (F). Because it’s a hydrous mass insulation, using calcium silicate on cold applications isn’t recommended. Attempts can be made to "waterproof" calcium silicate with silicones or other compounds, but it remains a poor choice for below ambient applications due to its thermal performance at this temperature range.
The support saddle often falls under the mechanical contractor’s scope. It’s also commonly included in the insulation sub-contract. The insulator then has to fill in the saddles with support blocks, insulation, mastic, and/or vapor barrier jacket. This is time consuming, to say the least. After these steps are taken, the final fit and adjustment of the hanger is still the responsibility of the mechanical contractor. The insulated saddle speeds up the total installation process for the insulation contractor and thus accelerates the turnover and billing cycle, along with eliminating a notorious punch-list item from the end of the job.
Benefits of Insulated Saddles
Insulated saddles are a complete composite assembly, allowing for fast and simple installation. They require significantly less labor to install than a field-assembled support system with separate insulation, support inserts, vapor barrier and support saddle.
Insulated saddles save energy because they improve thermal performance by improving thermal efficiency at hanger locations. Saddles for cold applications should have a 360-degree section of properly selected high-performance foam insulation. This feature reduces operating costs for the entire life of the thermal system. The insulation should feature a longitudinal lock-joint seam where possible, to provide a longer offset thermal path to the cold pipe surface.
All cold service saddles should have a minimum 6 mil thickness film vapor retarder unless ASTM E84 compliance requires a laminated foil based all service jacket type barrier. This feature should incorporate a self-sealing-lap. Selection of a high-performance vapor retarder reduces the likelihood of condensation problems, and the damage to buildings that can result from condensate leakage.
The 180-degree steel saddle used to support the assembly should be flared at both ends to provide maximum insulation (and vapor barrier) protection at all hanger locations and be constructed of highest quality rust-resistant G-90 galvanized steel (or type 304 stainless steel alloy where required) in 22 through 12 gauge thickness, depending on pipe size to provide positive hanger security and aid in rapid installation.
Bare hangers with the notorious metal-to-metal contact problems, or improperly installed field-insulated shields and supports, can compromise the thermal integrity of an insulated piping system. By leaving a large amount of under-insulated surface area, traditional methods and materials can increase operating and maintenance costs over the lifetime of the system, especially on cold piping. A properly selected insulated saddle will insure superior thermal performance at every hanger and support location. In addition to increasing thermal performance, it also saves expensive labor by reducing installation time. This is because every component is pre-assembled in its place and ready to perform; for the most part, no additional materials such as staples or adhesives are required to finish the job. No matter which trade jurisdiction the pipe saddles fall under, insulated saddles are available for smart designers, owners and installers.
Insulated saddles allow insulation to pass uninterrupted through the support area on roller supports for both hot and cold piping, creating a sealed thermal system where the traditional design (with the weld-on shoe-type saddle shown in Figure 2 or wood type saddles) prevent this efficiency from occurring. These saddles can carry a very high load in comparison to their weight, labor savings and thermal efficiency. For this application, insulated saddles should always have a heavy gauge steel (12 gauge minimum) support saddle, plus a structural steel support plate (1/4 inch thick minimum) for 6 inch pipe and larger, to distribute the load from the pipe to the roller over the saddle area.
The user should contact the insulated saddle manufacturer to verify that the product choice is appropriate for the application. Project specifications can sometimes be confusing, or even inappropriate. Forwarding a copy of the job specification to the manufacturer is always a good idea if the user has any questions.
This paper has discussed what can be inside a support location, what’s probably inside a support location and what should be inside a support location. Whether your applications are below ambient temperature cold piping, such as chilled water or above ambient temperature such as steam piping or condensate, there is an appropriate insulated saddle to fit your needs.
MSS-SP 58, Table 5, for type 40 shields.
|Pipe Size (inches)||Shield Length (inches)||Saddle Gauge|
|.25 – 3.5||12||18|
|5 – 6||18||16|
|8 – 14||24||14|
|16 – 24||24||12|