#39168 - 11/24/10 12:39 AM
Hot load adjustment in Spring Hanger Table
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Member
Registered: 10/30/06
Posts: 86
Loc: India
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I am seeing most of the vendors are adjusting the Hot load in the spring hanger table and bring the loads on the equipment nozzle within the allowable limit.They are ordering the spring hangers based on this and installing at site too.
After while removing the nuts of the spring hanger, the pipes are getting disturbed because of actual cold load.
It is very difficult for me to educate the vendors in this, as they are quoting "We are following as per the CAESARII" I request COADE to describe about this in their Technical reference manual breifly.
Regards,
_________________________
Moorthy
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#39197 - 11/25/10 01:43 AM
Re: Hot load adjustment in Spring Hanger Table
[Re: Moorthi]
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Member
Registered: 04/22/05
Posts: 1453
Loc: ...
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While is true that the load can be adjusted inside Caesar, it is also true that your vendors have to comply with the Spring hanger manufacturer requirements. So you still can educate your vendors in this.
Regards,
_________________________
Dan
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#39214 - 11/25/10 10:29 PM
Re: Hot load adjustment in Spring Hanger Table
[Re: danb]
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Member
Registered: 01/02/03
Posts: 255
Loc: Australia
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It may not be related but I have to say this. In the earlier versions of Caesar II the weight of the equipment that needs to be carried by the spring hanger was not considered in the selection of hanger in Caesar II. So, the knowledgeable vendors did add the additional weight on to the cold pre-load to consider them in the spring application. Of course the will affect the hot load on spring as well.
In 2011 version of Caesar II the additional weight can be added. This is a good feature for especially small diameter piping and heavy appliances on them. But you need to know the additional weigh accurately. Otherwise the vendors again need to check the additional weight and make adjustment.
Hope this clarify some of the confusions.
Ibrahim Demir
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#39222 - 11/26/10 10:33 AM
Re: Hot load adjustment in Spring Hanger Table
[Re: Ibrahim Demir]
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Member
Registered: 10/30/06
Posts: 86
Loc: India
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Nope, already there is a option available in CII, i.e is Free node. You have to specify the node in your hanger program, and it 'll consider.
You can adjust the hot load...but before you should know what exactly the cold load. Take this instance, my cold load is 400 kg, the spring rate selected by CII is 10 kg/mm, and my movement is 10mm vertical. So, during operating condition the spring will take 500 KG.
In the above condition my loads on the nozzle are not within the limit..then i ll try to increase my hot load say 700kg to meet the requirement, then i have to select 30kg/mm spring rate if it is available.
The above will be a acceptable practice.. In any condition the cold load will not vary.
But my vendors are selecting randomly say 1000 kg hot load and they arriving 600kg cold load.
Hope you will understand my situation.
_________________________
Moorthy
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#39223 - 11/26/10 01:22 PM
Re: Hot load adjustment in Spring Hanger Table
[Re: Moorthi]
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Member
Registered: 04/22/05
Posts: 1453
Loc: ...
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Moorthy,
I do understand your position.
A software is a tool and do not replace the engineer. This you should make clear to your vendors. Caesar can not and should not be responsible for this.
Just to have something in your help, please read some instuctions given by some spring hanger manufacturers.
Carpenter Paterson
In keeping with generally accepted practice, we recommend that the actual pipe load is correctly supported when the pipe is in its normal working position. This ensures no abnormal or excessive forces, due to out of balance supporting effort, is transferred to the pipework in its stressed working condition.
Anvil
When the hanger is installed, its supporting force should be in balance with the portion of the piping weight assigned to it.
Lisega
If the travel stops are jammed, the load actually applied does not correspond with the theoretical adjusted load. (See Installation and Operating Instructions, Constant Hangers, page 1.23, item 4, in this regard).
4.2 Theoretical and actual condition If it has been ensured that all connections are actuated by load, the load suspended is completely taken over by the constant hangers or supports. If the actual load corresponds to the installed load and the piping system shows no signs of constraints, the planned equilibrium has been achieved. The travel stop plates can now be removed. In practice, however, slight constraints and hence certain load displacements in the piping system can hardly be avoided. The theoretically determined loads can also show considerable tolerances. Deviations resulting from this can lead, according to increased or diminished loading, to a corresponding jamming of the blocking pin in the upper or lower part of the blocking plates.
4.3 Load distribution The travel stop plates must never be removed by force! By loosening or tightening the connecting rods with a few turns of the load nut for constant hangers, or adjustment of the support tube for constant supports, the locked-up stress in the piping can be compensated so that the blocking pin is free. However, the geometrical layout of the piping must not be altered when balancing these stresses. Because the adjustment of one position can lead to stressing at another location, this procedure must be repeated if necessary at different points. For thorough control, we recommend as a matter of principle removing the travel stop plates only after all the blocking pins are free
4.4 Load correction If the blocking pins jam, and cannot be freed without displacement of the piping, significant deviations in the piping load can be assumed. The adjustment bolts of the constant hangers and supports can then be correspondingly set. Once more, this should be done from position to position, as described in point 4.3. If this is done correctly, load differences can be practically balanced out by this method. Any load adjustments must as a matter of principle be agreed on with the technical department responsible for the piping system. Any new load setting values should be indicated on the load scales and recorded.
I think that if you contact some manufacturers you can obtain more detailed instructions.
In any case you should include these things in your specification (stress and/or supports specification) then you will have a strong basis for future discussions. Your vendors will be more carefull with these things, I can assure you.
Best regards,
_________________________
Dan
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#39228 - 11/26/10 08:18 PM
Re: Hot load adjustment in Spring Hanger Table
[Re: danb]
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Member
Registered: 01/02/03
Posts: 255
Loc: Australia
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From my experience one of my vendor had to change the spring rate of the hanger due to the additional load at the support. Of course this changed my calculations completely. The spring hangers have some limitation in minimum and maximum loads for particular spring rate. The code is requiring maximum 25% of load/displacement change. So you need to watch all these in your calculation. Caesar II does it for you. But earlier versions of Caesar II did not add the ancillary weight. So vendor somehow have to do some adjustment. However, you can put new spring rate and ancillary weight (you can put a flange to represent the weight in your case) into your analysis, check if the system is acceptable with the new loads and spring rates (if changed). Otherwise what is done may be creating problem. Do your analysis if not satisfied talk to your superior for corrective action.
Hope it helps.
Ibrahim Demir
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#39232 - 11/27/10 02:12 PM
Re: Hot load adjustment in Spring Hanger Table
[Re: Ibrahim Demir]
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Member
Registered: 04/22/05
Posts: 1453
Loc: ...
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Ibrahim,
The real problem is the following. In the Operating load field it can be inserted whatever load the analyst want. In this way many stress analysts solve the problems they have with the nozzle loads. Maybe because of lack of experience, or maybe because they do not care. I saw a 36" line with a spring hanger with 300 kg operating load. Ancilary weight is a problem but people is a bigger problem.
When somebody review a stress analysis, normaly it is easy to spot a "fake" spring supports by looking at the displacement in SUS load case.
Best regards,
_________________________
Dan
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#39241 - 11/29/10 12:16 AM
Re: Hot load adjustment in Spring Hanger Table
[Re: danb]
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Member
Registered: 01/02/03
Posts: 255
Loc: Australia
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I get it. Sometimes everybody needs education. No-one should work blindly, that is why we are here to discuss the industry problems. We discussed similar problems in another forum earlier. Mainly the jobs needs verification, this does not happen. After producing the material take-off no-one checks what goes into the field. The pipe stress engineers is cut off the job right after the analysis done, etc.. etc..
We can not solve this problems indivudially, the client need to be more educated, and ask for everything.
Regards,
Ibrahim Demir
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