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Spring Support Used in Piping
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6/17/2016 Spring support Used in Piping
http://www.pipingengineering.com/springsupportpiping.html 1/7
Table of contents:
1. Why to use a Spring Support2. Types of Spring Supports 3. Terminology 4. Variable effort spring 5. Types of VES/CES 6. Selection of Variable effort spring 7. Constant effort spring 8. Selection of Constant effort spring 9. General notes and guidelines10. Points to remember11. Offshore applications 12. Spring vendors
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Spring Support Used in Piping 4 Comments
Spring Support
1. Why to use a Spring Support?
Any line operating at high temperature movesupwards/downwards (depending on the pipeconfiguration) due to thermal expansion. Any rigid supportprovided on such a line tends to lift pipe up/down andhence remain inactive during operating conditions. Insuch a case a flexible support (springs) is provided whichis capable of taking the load in all the operating and coldconditions.
The spring supports provides continuous support duringexpansion or contraction of the pipe.
The spring support basically employs a spring element,which can get compressed or stretchout depending uponthe thermal movement of pipe and the correspondingloads.
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6/17/2016 Spring support Used in Piping
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2. Types of Spring Supports
Depending on the loads to be accommodated and the magnitude & direction of the thermaldisplacement to be supported, spring supports are broadly classified as:
Variable effort springsConstant effort springs
Some of the common terminology associated with the selection and procurement of anySprings are listed below:
Cold Load
Hot Load
Spring Rate
Spring Travel
Load Variation or Variation
Precompression Length
3. Terminology
Cold Load: This refers to the load on the spring hanger when the system is in standby ornonoperating condition.
Hot Load: This refers to the actual load on the spring hanger during operating conditionsSpring Rate/ Stifness: This refers to the spring rate, force per unit length in N/mm, kg/mm,etc. determined from flexibility analysis.
Spring Travel: (Installed to operating): This refers to the maximum vertical movement of thespring due to piping loads at operating conditions determined from flexibility analysis.
Load Variation or Variation: This refers to the allowed variations between the hot load andcold loads.
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6/17/2016 Spring support Used in Piping
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PreCompression Length: It is the initial compressing of the spring for sustained load.Installation Height = loaded length – Precompression length
4. Variable effort spring
VES basically consist of a spring which can get compressed or expanded according tothermal movement of the pipe. However, this movement causes increase or decrease insupporting force depending on its stiffness & this differential load is transferred to the pipe
This load is less than that would be with the rigid support.
In VES load variation is maintained generally within 25%.
In VES the loads increases with pipe movement.
5. Types of VES/CES
Hanger type: In hanger type spring support, the pipe is hung from the secondary support usinghanger type spring, as shown. Clevis, Hanger rod, turnbuckle, pipe clamp, etc. are some otherattachments associated with such a support.
Bottom support type: In bottom support spring, the pipe is resting on the top of the spring loadplate, as shown. This type of spring support is also known as ‘CAN’ Type or ‘F’ Type spring.
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Hanger type or bottom support type is selected based on pipe layout and the spaceavailability for mounting.
6. Selection of Variable effort spring
1. Determine the required effort & pipe movement (up or down) from installed to operatingcondition.
2. Select the smallest spring size from the vendor catalogue which has the operating loadwithin the working travel.
3. Ensure the spring selected can accommodate the preset to operating travel within theworking range. This is done by moving up & down the chart from the operating load by theamount of travel.
4. If the spring selected cannot accommodate the movement try a larger spring size or thenext travel range.
5. Check the variation in supporting effort for the selected spring.
6. If this exceeds the allowable variation then choose the next travel range and go back to Step3 above.
7. If the variation is less than half of the allowable then a smaller travel range may beacceptable. Choose a smaller travel range and go back to step 4.
8. If the variation exceeds the allowable selection then a constant effort support is required orpossibility of routing changes to be studied.
Example:
Select a variable spring for the following conditions:
Hot load = 307 lbs, movement = ½” up, variability = 20% maximum
1. Calculate spring rate.
Spring rate = hot load x variability / movement
= 0.20*307/0.5 = 122.8 lbs per inch
2. Find the spring size column on the size and series selection chart where the hot load is 307lbs.
(A size 5 series fig.82 fits the criteria)
3. Calculate the cold load.
Cold load = 307 + (63 x 0.50) = 339 lbs.
4. Now check to see if the hot load and cold load fit in the working range of size 5 series fig.82.If so, you have selected the proper unit.
7. Constant effort spring
Whenever load variation exceeds 25% or exceeds the specified maximum load variationpercentage in a variable hanger, then a Constant Effort Spring is selected.
In CES the load remains constant when the pipe moves from its cold position to hot position.
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Thus irrespective of travel the load remains constant over complete range of movement.
The pipe is supported by a drop rod connected via turnbuckle to the end of the lever arm.
The spring coil applies a force to the trunnion arm of the lever which tends to pull the leverarm UP against the load of the pipe.
The geometry of the lever arm provides a balance btw the pipe load & spring force. The pipemay therefore move due to thermal expansion while being supported with a nominallyconstant force through this travel range.
8. Selection of Constant effort spring
Determine the load to be supported by hanger as well as the actual travel, ie. The actualvertical movement of the pipe at the point of hanger location, refer loadtravel table.
The total travel for constant supports should be equal to “actual travel” plus 1” or 20%whichever is greater.
After determining the size, consideration of available room for suspending the pipe andhanger will indicate whether a vertical or horizontal hanger is desirable.
After hanger size & design are determined, the type of constant support to be used dependsupon the physical installation required by the suspension problem.
Example:
Total travel = 4 “ and 2750 lbs
Hanger size would be 34
9. General notes & guidelines
Any readjustment of spring element shall be carried out only when the line is full with thefluid or its equivalent in density to balance the weight of piping and the preset load of spring.
The adjustment of hanger type spring element is done by rotating turn buckle or adjustmentnuts provided in the hanger rod.
During hydraulic testing, flushing or chemical cleaning of the pipeline, the spring must bekept under locked condition or protected against overloading due to weight of testing /flushing fluid, by providing temporary.
After readjustment it is important to check whether sufficient range is available on scale forrequired movement of the pipe during operation.
10. Points to remember
Design spring based on the installation load (operating load).
Compactness of the units. Installation heights designed to a minimum.
During occasional case the pipe may move more than the operating movement. In such acase, if we choose maximum deflection range the spring cannot get further movement andthus the spring fails. To overcome such a problem provides “Cushion Range” means even ifin occasional cases the spring may get compressed, so choose always “MIDRANGE”.
Initial design itself the spring cannot be designed for occasional loads (e.g. Seismic, windetc.) & movement then it may be an over design.
For hanging spring support the lateral movements (rod swing) should not exceed 4 degree.
For bottom type supports, where horizontal movement of more than ½” is envisaged, Tefloncovered load pads should be specified.
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Always mention the hydro test load, while ordering a spring. This will help the spring vendorin designing the spring locking arrangement.
Standard inventory finish: Hot dip galvanized.
Coils come with a protective coating :Protects from a wide range of corrosives.
Does not affect the flex life of the spring.
Supports are fitted with nameplates marked with the installation and operating load, supportreference mark, type and unique serial number.
11. Offshore applications
Flow arm lines (X’mas tree to the production/ test manifolds).
Compressors.
WHRU (Waste Heat Recovery Units).
12. Spring vendors
Sarathi
Carpenter and paterson Ltd
Lisega
Anvil
Bergen power
Pipe support Ltd
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4 COMMENTS
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February 4, 2015 at 8:32 pm
Burt's Bees
Cool article, It was practical.Reply
May 24, 2015 at 6:10 pm
TALAL
hoe we can calculate the pipe weight on pipe supportReply
August 21, 2015 at 7:46 pm
Piping engineering
Hi Talal, For Stress critical lines pipe loads are calculated based on stress analysis inCeaser II software.
Reply
6/17/2016 Spring support Used in Piping
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March 28, 2016 at 8:10 am
jung
Cool article, It was practical.Reply
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