Counterpoise Constant Support Hangers 1

[engrpiper]

I have a job to review a main steam line in a 1950's power plant. They have "Counterpoise Constant Support Hangers" from Basic Engineers. I have found reference to these in the National Valve and Manufacturing Company, NAVCO, book. However, support type, size, travel, load are not listed in the NAVCO book. Does anyone have information or know where to get info about the counterpoise supports?

Thanks in advance for your answers.

 

[RossABQ]

These are generically called constant support hangers. Grinnell and others still make them. There should be a tag on the existing hanger giving all the info you need.

 

[NozzleTwister]

I have a Basic Engineers Counterpoise catalog but it's hardly 1950s vintage. Mine has a print date of 1985 but maybe not much has changed.

Depending on the info you're looking for, you can post here and I'll try to respond. You'll need, SIZE, TOTAL TRAVEL and SPRING TYPE (B, S, V, VBS, VB, U, etc)

NozzleTwister
Houston, Texas

 

[JohnBreen]

This is not a trivial topic.

There is no getting around it you first have to get up there and take the data from every name tag on each hanger. In many cases, hangers have been replaced through the years after the original hangers were installed (for various reasons and by various parties). Consequently you often cannot trust the original drawings. There is no substitute for looking at each hanger yourself and recording the data from the name tag. You can then post the data here and NozzleTwister will give you the hanger data you need to do the evaluation.

Keep in mind that in the 50's it was common for "approximate methods" to be used to calculate the loads at the hangers. Today, with modern software you can do a MUCH better job. Also keep in mind that the original hangers have aged and they will not likely perform as they did when new. For example, the springs in these hangers will, due to several reasons, no longer provide the (specified) supporting forces that they did when new (they will have "relaxed"). The old hangers will also suffer from increasing internal friction that has increased since the hangers were new (due to corrosion and break down of the original lubricants). As a consequence of the additional internal friction the spring hangers will perform erratically. As an example in a system where the pipe will move vertically up in going from cold to hot, the hanger (with internal friction) will "under support" as the pipe moves up to its hot position and upon going hot to cold, the hangers will "over support". This will result in the dead and live weight being distributed to adjacent hangers and structures. This will also result in unpredictable loadings on the turbines, pumps and boiler nozzles.

As an additional consideration, you should know that pipe for many systems of this era was specified to a "minimum wall thickness" specification. The pipe mills in order to assure that the pipe would meet the "min wall" requirement at bends most often would make ALL the pipe thicker. It is not unusual to find high energy piping systems in power plants built in the 50's and 60's have pipe wall thicknesses that are 20 to 25 percent thicker than the minimum wall specified. Of course the original pipe hanger designer may not have known this and the hangers supplied would be undersized. Also, look for damage to the hangers, and missing parts. Also look for indications that the hangers have been "adjusted" for changes in the pipe elevation or (worse) have had their original reactive force "adjusted" internally to provide less or greater supporting force.

I have done an EPRI hanger maintenance seminar that discusses all thes things (and more) and if you are an EPRI member you can go to thier web site and download the presentation.

Regards, John.

 

[RossABQ]

Very good points, John!

Even on more modern systems (say pre-1975) computer analysis was not common. Valve and fabricated fitting weights on piping systems of custom-wall pipe are rarely accurately accounted for in even computer modeled systems.

I went thru 4 power plant critical piping systems in a previous career, top to bottom, using load cells to "as-built" the pipe loads hot/cold, and to test the hangers throughout their ranges. Individual hangers were as much as 20% off their nameplate loads. Several were found to be stuck due to linkage or spring damage. The pipe loads were as much as 10% off design, fabricated Wyes being the apparent culprits. The plants were only 10 - 12 yrs old at this point. The unbalanced support systems were causing the piping to load the turbine nozzles unevenly, enough to cause misalignment (rubs) and balance problems.

 

[JohnBreen]

Hello again MSandersEng,

I should have mentioned that Anvil-Grinnell has a FREE hanger design manual available that will give you a lot of design background and some valuable design data. You can download it here:

http://www.anvilintl.com/db/catalogs/Pipe_Hanger_Design-05.pdf

Regards, John

 

[0707]

For constant spring hangers go to

http://www.lisega.de/cms/component/option,com_frontpage/Itemid,1/lang,en_E

N/

luis

 

[DSB123]

0707,
The thread is about information about a particular make of spring which is in service not a request for a sales pitch!!!