RE: spring hanger

From: <Tony>
Date: Mon Aug 13 2007 - 14:16:00 EDT

Regarding spring travel change from 40 to 76mm:

Increases in travel are often from short to standard springs, which are available off-the-shelf. Springs with longer travel generally accommodate shorter travel, so there's no problem with the upgrade. Additionally, the longer travel springs have smaller stiffnesses, and so the load variation when going from cold to hot conditions is smaller.

Manufacturers don't provide exactly the same springs, but it looks like your contractor wants to go from a standard to a double spring?

If this is true then perhaps either:

1. The contractor is doing the pipe stress for you and wants to lower the load change on equipment.
2. The double spring is available while the standard spring is not.
3. The calculated travel is outside the 40mm range from the stress analysis and this error was just discovered.

You wrote that your company spec requires going to constant springs when the movement is greater than 40mm. Generally this is a function of attached equipment, number of cycles of operation, configuration, temperature and cost. Constant effort springs are less forgiving of inaccuracies in the weight calculation and more expensive than variable springs. If the attached equipment is a vessel nozzle and there's little cycling, then use of a constant effort is often not warranted. Systems in the creep range can often drag constant effort springs around with them causing the spring to bottom out.

More information about the type of system would be helpful, i.e.

1. What is being protected by the spring, i.e. stress in the pipe, a pump, or a vessel nozzle, etc.?
2. Is the system in cyclic service?
3. Who did the pipe stress analysis?
4. How many springs are involved in the change?
5. Are there many other springs in the immediate vicinity?
6. What is the operating temperature?
7. Will there be large occasional swings in temperature?
8. Are there multiple operating states to be accommodated?
9. What is the calculated spring maximum travel and computed cold load?

Tony

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From: PipingDesign@yahoogroups.com [mailto:PipingDesign@yahoogroups.com] On Behalf Of nastaran Lotfifar
Sent: Monday, August 13, 2007 8:55 AM
To: PipingDesign@yahoogroups.com
Subject: [PipingDesign] spring hanger

Hello every body
there is a note in our specification in our company as follows: " when thedisplacement of the piping, between the erection and the service position, at its point of supports, is greater than 40mm, constant-lift hangers and supports shall be given preference over variable-lift hangers and supports."
our contractor want to change 40mm to 76mm. what do you recommand. please let me know your comments and experiences.

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Received on Mon Aug 13 14:16:00 2007