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  Webinar Archives > Engineered Spring Supports

Engineered Spring Supports Webinar (January, 2009)

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Text Version of the Engineered Spring Supports Webinar

For those unfamiliar with us, we would like to share some background information on our company. Our parent company, Piping Technology & Products, Inc., also known as PT&P, has been in business since 1975. PT&P and its wholly owned subsidiaries, US Bellows, Sweco Fab, Pipe Shields, and Anchor Darling, offer a wide range of engineered products and services for various industries and applications. Our product line is extensive, from spring supports, expansion joints, pre-insulated pipe supports, and miscellaneous fabrication to various engineering and technical services, PT&P has decades of experience providing products and services for all your engineering and construction needs.

We have achieved various certifications here at Piping Technology & Products. We have the ASME U-Stamp and R-Stamp for the SWECO division of our company. We are ASME NS certified in our Fronek Anchor/Darling, Enterprises division. We are also part of the Expansion Joint Manufacturers’ Association through our U.S. Bellows, Inc. division. Most recently we received the ISO 9001:2000 certification for the manufacture of hot and cold supports. We are a Minority Business Enterprise granted by the City of Houston, and additionally, we are a member of the Houston Minority Business Council.

Our headquarters is here in Houston, Texas. Our facility is located on a 35 acre property including additional room for future expansion. We are just miles away from the Port of Houston which allows us to quickly and conveniently ship to a variety of countries throughout the world.

This presentation is about PT&P’s engineered spring supports product line. Additional information can be found in our online catalog here.

variable spring hangers
The main purpose of an engineered spring support is two-fold: 1.) To uphold a specific load, including the weight of the pipe, commodity, flanges, valves, refractory, insulation, etc. 2.) To allow the supported load to travel through a predetermined thermal deflection cycle from its installed condition to its operational condition. Variable spring supports are used where: 1.) Relatively small thermal deflections, usually less than or equal to 2" are anticipated. And 2.) A difference in the supported load from the installed to the operating condition is acceptable.
We carry a substantial amount of variable springs in our inventory which can accommodate loads up 5,000 lb. “Big Ton” springs are used for very large load conditions where standard variable springs are too small. Constant spring supports are utilized when: 1.) the supported load cannot vary between the installed and operating position. And/or 2.) Large thermal growth is anticipated.

The three main types are:
1.) Variable Spring Support: designed to support piping from below, directly from the floor or supporting steel. Adjustment is made by inserting a bar into holes in the load column and turning the load column as a jack screw. The base plate is bolted to the case and has four holes for fastening.
2.) Variable Spring Hanger: designed to support piping from above.
3.) Constant Load Hanger: typically used to support piping subject to vertical movement.

Variables use coiled springs to support a load and allow movement. The resistance of the coil to a load changes during compression, which is why these devices are called variables. There are many different designs for variable supports; we use A through G to describe seven different physical connections to the supporting structure. A-E and G are hangers suspended from structural members and type-F is a base support that rests on the supporting surface. All of our variables are available in short springs, standard springs, double springs, triple springs or quadruple springs.

Type-A variable spring supports are furnished with a threaded bushing in the top plate, providing for a simple rod attachment for the upper connection. Type-B and Type-C variables are furnished with one or two lugs welded to the top cap plate of the casting. Type-D variables permit adjustment from the top, by turning the nuts on the hanger rod against the load column which protrudes through the top. Type-E variable springs permit rod adjustment from either above or below the spring. This type of spring can be set above the supporting steel. Type-F springs are designed to support piping from below, directly from the floor or supporting steel. The base plate is bolted to the case and has four slots for fastening. An interesting feature of F-type variables is that the installed height can be adjusted independently of any load adjustment. A Type-G spring support assembly is formed by welding two standard spring assemblies to the ends of a pair of channels. This type of variable can accommodate unusually heavy loads and is adaptable for avoiding interference in spaces where headroom is limited. Travel stops are inserted and strapped in place to maintain the load for the assembly installation. Sometimes the travel stops will be chained to the spring housing. This is an optional feature available on all spring supports which prevents loss of the travel stops after the assembly is put into service.

The steps in loading a spring can are as follows:custom designed variable spring
The first step is to check the hot and cold loads on the assembly drawing.
The second step is to compress the spring to solid and release three times total.
Then you will need to zero out the load cell before you compress the spring to the specified cold load.
Mark the cold load location on the can, then measure for the travel stop length.
Next you will need to compress the spring to the specified hot load.
Mark the hot location on the spring can, then measure the distance between the loads.
The distance should match the desired travel.
Compress the spring to the cold load and place the travel stops in.
Release the load and check the travel stops.
Remove the spring from the cage to a table using a hoist.
When adding the name tag and straps, first you need to drill and hammer the rivets into place.
Measure the remaining slot for hydro-test stops.
Put the stops in place, strap them down, measure, and lastly, adjust the load flange height if necessary.

Big ton springs are custom designed to meet load and travel requirements for very large loads using a multiple coil system. Usually a base-mounted support that can be designed with slide plates for lateral pipe movement. The height, width and length are also custom designed to meet space requirements.
Now lets switch gears and learn more about PT&Ps constant spring supports. Constants are used when the load variability between the hot and cold loads exceed 25%, and/or around sensitive rotating equipment where a load variation could be harmful.

Example 1: PT&P designed figure 200 U-type constants fabricated from A36 carbon steel and designed to handle a load of 24,000 lb. These particular constants are capable of 3 of total upward travel.

Example 2: PT&P designed figure 200 U-Type, upthrust constants with exceptionally large travel for a geothermal plant. They measure 12 in length and 4 in height. The customer required the constant load to be 2400 lb. with 46 of travel.

Horizontal constants are used mostly when vertical space is not available; the spring can is aligned horizontally, while permitting vertical movements. The figure 200 A-type constant is useful where the rod take-out is small and will be bolted directly under the beam eliminating the space used up by the mounting lugs. Vertical constants are used mainly when horizontal space is not available. PT&P figure 100 B-Type vertical constant uses double-pin suspension instead of single-point suspension. This will eliminate any constant rotation as the pipe moves due to thermal expansion.

Base mounted type constants are called F-Type and U-Type or upthrust constants.
F-Type: Some translational movement of the load table as it is traveling up and down.
U-Type: The load table travels straight up and straight down by means of the rotor assembly

Example: Customized U-Type, upthrust constants designed to handle 6" of total travel and loads of 5677 lb. and 4956 lb. The load flange is modified to hold six ball transfer units for each support. The ball transfer units are used to decrease the coefficient of friction to 0.05 compared to using the standard PTFE, 25% glass filled, which is 0.15. Gussets are added under the load flange to maintain a leveled surface and an equal load transfer to all ball transfer units. These custom designed constant supports are manufactured for steam power plant superheaters.Constant spring support in the field.

Pipe Hangers are designed to control:
Longitudinal weight stress in the piping system without creating additional stresses
Piping system loads on equipment without limiting or reducing static loads
Hanger loads on building structure
Physical clearances of hanger components with piping and structure

Lets look at the basic steps in the hanger design: Step 1 is to determine the location of all the hangers. Then calculate the hanger loads due to the piping weight. Next, calculate the thermal movement of the piping at each of the hangers location. Step 4 is to select the hanger type and finally check all clearances. While installing, securely attach the spring to the existing structure per the spring support design. If required, attach a hanger rod to the fabricated load column or turnbuckle. Next attach other related hardware, for example, here is a constant in the field with the rod, turnbuckle, weldless eye nut and welded beam attachment. After hydro-testing, remove the travel stops as pictured here. The last step in installation is to verify that the load indicator is at the desired setting (cold/hot load).

Lets look at the average life expectancy of a spring hanger:
1.) An unprotected spring hanger will last anywhere between 15 and 20 years.
2.) If the hardware is galvanized, which is PT&Ps standard, the spring hanger will last between 15 and 30 years.
3.) And if the springs are coated with Neoprene, it will last 15 to 30 years.
Corrosion and fatigue are the main factors that contribute to the deterioration of a spring hanger assembly.

If the piping system has inadequate support, static loads can cause multiple problems, like:
1.) Leaking flanges
2.) Pump and turbine problems, mainly concerning the bearings, seals and misalignment of flanges
3.) Sagging lines and/or liquid trapped in low sections
4.) And an increase in system stresses can result in piping failures as well

When inspecting a spring support, the first thing you want to do is: Visually inspect each spring hanger in accordance with the ten point operational integrity check. Load indicator on a variable spring hanger.
1.) Beam attachment
2.) Beam attachment pin
3.) Spring hanger attachment
4.) Load flange movement
5.) Spring coil corrosion
6.) Check load indication for hot load
7.) Note load deviations
8.) Turnbuckle/locknuts
9.) Threaded rod/weldless eye, hex nuts
10.) Pipe clamp attachment pin
After the ten-point visual inspection, you should tag each spring hanger as good, adjust, or replace, and then issue a field summary report.

While our technicians were on field service calls; they observed many other supports not fabricated by PT&P with the following issues:
1.) Load indicator scales were missing or painted over. While it can be stated that the supports are taking load, it is extremely difficult for field personnel to distinguish the precise load these assemblies are holding.
2.) Settings on variable springs were incorrect by the load indicator lable located to the right of the spring.
3.) Some supports even had a 2x4 left under the pipe.
4.) A variable spring support was seen with the travel stop left in. Failure to remove the travel stops would lock the spring coil in position and render the support inoperable.
5.) A pair of base-type springs exhibited significant rusting of the spring coil. Extensive deterioration of the coils would alter the spring rate and ultimately reduce the load carrying capability of the assembly.
6.) Also observed were variable spring assemblies which have not been loaded. The load indicator at the top of the slot is a clear indication that either 1.) The springs have been unloaded and never returned to service or 2.) The assemblies were improperly sized for the load.

When deciding on whether to replace a spring can or not, consider:
1.) The spring hanger has no useful life remaining due to corrosion and fatigue.
2.) Rust damage makes it necessary to replace threaded rods, bolts, pipe attachments, etc.
3.) Equipment to be supported has been modified or changed from its original design.

In the case you want to use your existing spring support, re-calibration is an option as long as the support is a constant spring support, in good operating condition, has an operating load range greater than 15,000 lb. and the cost of field time and equipment is less than the cost of a new spring hanger.

To adjust a spring hanger after inspection, set the spring to the desired position by turning the turnbuckles and load column. When the nameplate is present indicating the design hot load, adjustments can be made during operation, but a cold load adjustment needs to be made during a shutdown.

Shutdown/Isolation Procedures
1.) The lines and equipment must have temporary supports while repairs are being made.
2.) Re-install travel stops when the line is taken out of operation (shutdown) to prevent line and equipment movement and possible re-adjustment of the springs.
3.) If re-calibration is recommended and the name plate is missing, the variable spring should be stenciled at the proper installed and operating positions or provide loads for re-calibration.
4.) Remove the spring hanger assembly.

Remember: When selecting springs, determine the location of the hanger, calculate the hanger load and the thermal movement of the piping at the location. For optimum performance, follow the installation guidelines from attaching the spring to the existing structure to setting the load indicator. When inspecting springs: Utilize the 10 Point Operational Integrity Check to make sure your springs are in good working order. Plan now to replace damaged and/or improperly sized springs that could ultimately lead to catastrophic failure.

 

 

 

 

 

 

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Mailing: P.O. Box 34506, Houston, TX 77234-4506 Location: 3701 Holmes Road, Houston, TX 77051
Our Subsidiaries: U.S. Bellows: Metallic & Fabric Expansion Joints, Bellows
Sweco Fab: ASME Vessels, Pig Launchers, Spectacle Blinds
 Pipe Shields: Pre-Insulated Pipe Supports, Slides, Guides & Anchors

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: Snubbers, Sway Struts & Sway Braces
Phone: (713) 731-0030 Toll-Free: (800) 787-5914 FAX: (713) 731-8640 info@pipingtech.com

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