PT&P designed and fabricated U-Type constant spring support , with PTFE, 25% glass filled side plate for a Polypropylene Plant in Texas. The constant is fabricated from carbon steel, and hot-dipped galvanized for extra protection against corrosion. The vertical movement is 1.5″ total upward travel and is capable of supporting a 10,350 lb. load. The constant underwent standard load testing prior to shipment.
PT&P designed these G-Type variable spring support assemblies, along with a 24” pipe shoe and hanger for an oil and gas refinery in Texas. Each item is designed with a center to center of 36” and an elevation difference up to 72”. The spring supports consists of a G-type variable spring, all threaded rod, clevis, lifting lugs, welding lugs and clevis pins. They are designed with an operating load range from 1,700 lb. to 10,500 lb. and a movement range of .02” to .19” up or down. Standard load and travel testing was completed prior to shipment.
PT&P designed C-Type variable spring support assemblies for a power plant in Louisiana. They are designed for operating loads ranging from 1,319 to 2,800 lb. with an upwards travel ranging from 0.11" to 0.34". The variables were fabricated from carbon steel with a hot-dipped galvanized finish and standard load and travel testing was completed prior to shipment
A constant spring support is a pipe support that uses a spring coil (or series of coils) to accommodate pipe movement from the initial (installed) condition to the final (operating) condition of the piping system. For all constant spring supports there is no difference in load and the supported load will remain uniform throughout the deflection cycle.
When the variabilityof a variable springexceeds the MSS standard of 25%, the designer's first option would be to lowerthe spring rate so that the difference in load with the same amount of movementwould be smaller than that associated with the higher spring rate. The designerwould continue this exercise until a variability factor of less than 25% isachieved.
Variability applies to variable spring supports and is basically a ratiobetween the difference in load and the operating load of the spring. Thedifference in load is a function of the spring rate and travel. Per MSS, themaximum recommended variability would be 25%. However, critical systems such asmain steam supports may require variability factors less than 25%.
A spring support jacking bolt is a variable spring accessory that aids inremoving the upper limit travel stops. They are usually used in applicationswhere large installed loads are present. They are located directly above theupper travel stop. By tightening the jacking bolt, the installed load can bemore easily transferred to the spring load column.
F-Type Variable with Jacking Bolts
This big ton spring support measures 40″ length x 36″ width x 43″ height. It is composed of a carbon steel frame, neoprene coated spring steel coils, and has a hot-dipped galvanize finish. It also includes a guided load table to ensure stability when supporting the maximum load of 93,000 lb. Standard load and travel tests were performed prior to shipping.
The design parameters that must be considered when selecting a pipe hanger would include operating temperature, operating load, movement, pipe material, available space, and allowable initial load requirements. Once these are known, then you can select an appropriate type of pipe hanger which could be any of the following types including rigid hangers, variable spring hangers, or constant spring hangers.
Variable Spring Hanger Installed in the Field
In order to set (load) a spring support, you must ensure that the pipe system is at its cold (installed) state. (All hydro-testing has been completed.) At this point, with variable springs, the lower travel stops should be removed. Adjust the load at the load column of the spring so that a load slightly above the cold load is reached. The remaining travel stops can now be removed. Note: Excessive force should not be required to remove the travel stops at this time.
For variable springs there are 23 sizes with loads ranging from 50 lb. through 50,000 lb. For constant springs, there are 110 sizes with travel ranging from 1″ to 14″ and loads ranging from 0 lb. to 90,000 lb.
PTP-8 Type C Variable Spring Assemblies
Figure 100 C-Type Constant Springs
PTP 100-C Size 84 Constant
There are different ways to attach a spring support to a rod. For A-Type constants and variables, you need two separate rods. The top plate of the assembly includes a threaded piece that will connect to an upper rod. A second rod will be connected to the bottom by the spring's threaded load column. For B-Type and C-Type constants and variables, you need one rod to attach to the spring assembly's threaded load column. For D-Type and E-Type variables, a single rod runs from the bottom through the top of the spring and hex nuts are used to secure the rod in place. For D-Type and E-Type constants, a single rod is attached using a turnbuckle.
Variable Spring and Rod Assemblies
In order to remove a spring support, first you must ensure that the spring is at its designed cold (installed) position. Next, re-install the travel stop(s) in the support. Then, provide adequate temporary support for the piping system. Once you have adequate support, you can release the load from the spring. Finally, remove the spring support from the piping system.
Variable Spring Support with Travel Stops in Place
To check the load setting, examine the position of the bottom of the load indicator with respect to the scale on the spring's tag. Read from the bottom of the load indicator to determine position. Next, look at the size of the spring located on the tag. Then, refer to the appropriate load and travel table (Constant Load & Travel Table or Variable Load and Travel Table) to determine the respective spring rate and the “0” load (minimum working range load). Multiply the spring rate by the position value and add that to the “0” load value.
In order to size a constant spring support, you must know the load and the anticipated travel. From that you can determine the amount of total travel and then refer to the constant spring support load and travel table to locate the correct size spring for your design.
Constant Spring Supports with Neoprene Coating
In order to size a variable spring support, you must know the cold load, the hot load, and the amount of travel of the pipe system. From that you can determine the required spring rate, and then review the variable spring support load and travel table to locate the correct size spring for your design.