Cold springing 1

[drudland]

i have a question... i was under the impression that the process of cold springing was not the desired way of producing piping flexibility. Are there any references or rules about cold springing... when or when not to use it?

 

[donf]

Drudland,

It's been a while since I was involved with the issue of cold springing - so I don't know the current industry position. But I can relate a potential "trap".

I overheard a mechanical contractor complaining about the poor fit-up of some previously installed piping. When a set of flanges was unbolted, the pipe "sprung" back about 2 inches. The contractor was about to "fix" the apparent fit-up problem by adding some pipe. Fortunately, I was able to track down the documentation that identified that loop as intentionally having cold spring.

If you do decide to employ cold springing, figure out how to prevent someone from "fixing" it at a later date.

Regards,

Donf

 

[zeven]

Cold Springing, reduces the max thermal loads (and stresses) in a system, by introducing a predetermined stress in the pipe when it is cold. Its main purpose is to reduce the peak loading on connecting equipment.
However it does not effect the overall stress range, and therefore it cannot be used in the stress range equations.
In piping systems well below the creep range, any cold spring should stay for life.
Pipes in the creep range will eventually fully relax out, so they will become 100% cold sprung, regardless of how much you apply at original build stage.
Some codes, such as BS806, makes use of cold spring to reduce the maximum hot stress (deaweight+pressure+thermal expansion).

 

[drudland]

donf and zeven

Thanks for the responses. Do you know of any published literature on the pros/cons of cold springing?

 

[zeven]

I'm sorry I don't.
I have done it myself in the past on High pressure high temp steam pipes operating in the creep range.
Basic rules to follow are
1) Introduce a cold spring/pull in one direction only. It is almost impossible to put it in, in more than one direction at site.
2) Don't use more than 2/3 of the estimated thermal movement
3) don't use cold pull where the thermal movements are relativley small. Again it is very dificult in practise to install to such accuracy, and small amounts suggest the piping system is very stiff, and not correctly designed.
4) Supply the erection contractor with a detailed procedure about how to introduce the cold spring/pull (Which pipe to hold, which springs to unblock etc.)

Hope this helps

 

[DLANDISSR]

drudland:
Both ASME B31.1 and B31.3 have statements about cold spring. They do not give any advise on when and how to apply cold spring.

ITT Grinnell Industrial Piping, Inc.'s book "Piping Design and Engineering" has a statement on Cold Spring.

Basically cold spring is used to:
1. Minimize the offset of a piping system from the neutral position (installed position without cold spring)to the operating condition. For Example:
If a pipe moves 2" from the neutral to the hot position and it is cold sprung 1", the offset from the neutral positon when cold will be -1" and in the hot position +1". So the offset from the neutral position with cold spring is 1", and 2" without cold spring.

2. Minimize the forces on an end point which may be at a piece of equipment. Since a negative force is put on the equipment in the cold position the pipe will pass through a neutral force condition during heat up and have a reduced force in the hot or operating position.

3. Reduce the stess in the hot position. Since a negative stress is placed on the pipe when installed with cold spring and during heat up the pipe will relieve this initial stress and pass through a neutral stress condition the final stress in the hot position will be reduced.

Since the stesss range from cold to hot is still the same, Viz. Say o to 10,000PSI or -5,000 to +5,000PSI, the range of 10,000 is still the same. No credit can be taken for reducing the stress by cold spring in the stress calculation. This is because the failure of the pipe due to hot and cold cycles is due more to the stress range it passes through than final stress.

As a rule of thumb the cold spring should not be more than 1/2 the expected or calculated movemment.

4. Minimize hanger movement. If a hanger is on a pipe that moves, for example, 2" horizontally then the hanger will be dislocated from its neutural position 2"without cold spring. Normally the hanger offset and rod length should be such that the hanger rod will not be offset more than 4Deg.

If 1" of cold spring is installed and the hanger is moved -1" from its neutural position and in the hot position it is +1" from the neutral position then the rod could be half the length and still be within the 4Deg limit.

If the hanger offsets more than 4Deg the uplift will become a factor and induce more load and stress at the hanger point and possibly at equipment connections.

Good judgement must be used when applying cold spring. Since the cold spring becomes a vital part of the design extra precautions and field verificaions must be used when actually installing the pipe to insure that the cold spring is installed as designed.

 

[drudland]

Thanks guys

In your opinion.. is cold springing a good idea, or should it only be used if the piping flexibility can not be increased another way??

 

[robinxie]

In my opinion, cold spring is always the last choice. If you can use expansion loop or expansion joint, do not use cold spring.

 

[MJCronin]

drudland,

"Cold-springing" of piping is not a good idea..........It is basically a design/installation technique left over from the 1950s. It was most often used to reduce piping reactions on equipment in Main Steam and Hot Reheat piping systems in coal fired power plants.

The actual "cold-springing" of large diameter, heavy walled piping systems is very hard to control and properly document. If a piping contractor does this improperly, ( and most are inexperienced)it can cause much more harm than good.

As stated above, the B31.1 piping code allows a reduction in the calculated piping reactions on equipment with cold sprung piping, but not on the calculated stresses.

If you really want to reduce piping reactions at equipment, consider a re-route of piping or the addition of rigid pipe supports. A detailed piping stress analysis program is required to evaluate alternatives

The "Piping Handbook" by Nayaar has a page about coldspringing of piping and suggests that there are other ways to accomplish your goals.

just my thoughts/recollections....



MJC

 

[DLANDISSR]

drudland:
Cold Springing like Expansion Joints should be a last resort.
If reduced movement or lower equipment loads cannot be achieved by rerouting the pipe, limiting stops and supports
then cold springing may be the answer.

Cold Springing is difficult to accurately achieve in the field. If used the Cold Spring should be carefully inspected during installation to insure the design has been accurately implemented otherwise it is usless.

It is not that Cold Spring is a bad idea. It is a useful tool but has some pit falls. Careful consideration must be given during design and proper installation insured.

During installation the piping has to be completed with all hangers in place and properly adjusted but without the appropriate equipment connections made up. The offset, due to the Cold Springing and then be measured accurately before the final connection to the equipment.