PT&P manufactured 266 variable spring supports for a refinery in Texas. The variable spring hangers include chained travel stops for ease of disengagement and reinsertion during plant shutdowns. Variable springs (a type of Compression spring) are used in a wide range of applications (including various Low Carbon Capital projects, CO2 removal units, and Infrastructure improvements) to support the piping system. The variables are fabricated from carbon steel and hot-dipped galvanized to protect against corrosion. The PTP-2 variables were designed for loads up to 13,850 lb. and movements up to 0.1875” upwards. The PTP-4 variables were designed for a maximum load of 15,050 lb. and movements up to 0.8125” upwards. Each spring hanger underwent standard load testing and QC tests. PT&P also provided constant supports for loads that remain uniform throughout the deflection cycle and sway struts for controlling vibration and shock loading while restraining movement due to thermal expansion for this order.
PT&P received a rush order this past week for variable spring supports at 4:41 pm, quite late into the workday; however, this is business as usual, our manufacturing facility in Houston, TX operates 24/7 to support our customers.
In this case, the customer facility, an olefins plant was incurring a significant loss and needed to replace the springs to resume operations as quickly as possible. The seven (7) variable springs were designed, fabricated, and shipped within 2 days. The F-type variable spring support is designed to support piping from below, directly from the foundation, concrete column, or supporting structural pipe rack steel. Adjustment is made by inserting a bar into holes in the load column and turning the load column as a jackscrew. The base plate is bolted to the case and has four holes for fastening.
As global leaders in variable spring manufacturing, we used our adaptive manufacturing processes in which the PT&P pre-fabricated component parts that make up these variables are easily assembled when orders are placed. These variables were fabricated from carbon steel and hot-dipped galvanized for corrosion protection. They are designed to support loads ranging from 713 lb. to 1668 lb. and movements of 0.148” to 0.133”. Load and travel tests, along with Q.C. inspections were performed before shipment. Variable springs are used in mills, refineries, chemical, plastics, polymer, solar, power, biochar, renewables, carbon black, LNG boilers, food, packaging, and wastewater treatment plants to support piping as it goes through its’ range of movement.
|Type:||F-Type Variable Spring Support Assemblies|
|Design:||Operating Loads from 3000 lb. to 4000 lb.
Movement of 1”
|Testing:||Load & Travel Test | Q.C. Inspection|
Pictured here is a Type G variable spring hanger assembly designed for an operating load up to 4000 lb. and 1” movement. This type of support assembly is formed by welding two standard spring assemblies to the ends of a pair of channels. The Type G assembly is especially adaptable for avoiding interference in spaces where the headroom is limited. The assemblies are fabricated from carbon steel and underwent spring load tests before shipment.
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
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
Use this 10-point operational integrity check list when inspecting spring supportsin the field:
- Beam attachment
- Beam attachment pin
- Spring hanger attachment
- Load flange movement
- Spring coil corrosion
- Check load indication for hot load
- Note load deviations
- Threaded rod/weldless eye, hex nuts
- Pipe clamp attachment pin
Corroded Variable Spring Support
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.