Enable this check box to cause CAESAR II to make one additional pass after the hanger design is completed and the hangers are installed, to determine the actual installed loads that should be used when the hangers are first installed and the load flanges adjusted in the field. This calculation tends to be important when the stiffness of the piping system is small, the stiffness of the hanger selected is high, and/or when the hanger travel is large (i.e. this usually is more important in smaller diameter piping systems that for some reason are spring supported away from equipment nozzles). Actual cold loads should definitely be calculated when springs in smaller diameter lines are to be adjusted in the cold position.
Allow Short Range Springs
CAESAR II gives the user the option of excluding short range springs from consideration from the selection algorithms. In some instances short range springs are considered specialty items and are not used unless their shorter length is required for clearance reasons. In this case, this check box should be cleared by the user.
If this option is not activated, CAESAR II will select a mid-range spring over a short-range spring, assuming they are more standard, readily available, and in general cheaper than their short-range counterparts.
If the default should be that short range springs are used wherever possible, then check the box on the Hanger Design Control Spreadsheet.
Allowable Load Variation (%)
This is the user specified limit on the allowed variation between the hot and cold hanger loads. If not specified, the only limit on load variation is that inherent in the spring table. This is approximately 100% when the hot load is smaller than the cold load, and 50% when the hot load is larger than the cold load. Hot loads are smaller than cold loads whenever the operating displacement in the Y direction is positive. The default value for the load variation is 25%. The user is advised to enter this value in the Hanger Run Control Spreadsheet before any hangers are defined.
The Allowable Load Variation is the percentage variation from the hot load:
(Cold Load) - (Hot Load) Variation
Hot Load
=
or as may be more familiar:
(Travel Spring Rate)( ) Variation
Hot Load
=
The Allowable Variation is entered as a percentage, i.e. twenty five percent would be entered 25.0. The Allowable Load Variation can have different values for different hanger locations if necessary by entering the chosen value on the individual hanger spreadsheets or it can be entered on the Hanger Design Control Spreadsheet to apply to all hangers in the model.
Rigid Support Displacement Criteria
This is a parameter used to determine if there is sufficient travel to design a spring. The Rigid Support Displacement Criteria is a cost saving feature that replaces springs that are not needed with rigid rods.
The hanger design algorithm operates by first running a restrained weight case. From this case the load to be supported by the hanger in the operating condition is determined. Once the hanger design load is known, an operating case is run with the hot hanger load installed to determine the travel at the hanger location. If this determined hanger travel is less than the Rigid Support Displacement Criteria then a rigid Y support is selected for the location instead of a spring.
If the Rigid Support Displacement is left blank or zero, the criteria will not be applied.
The Rigid Support Displacement Criteria may be specified on the Hanger Run Control Spreadsheet, or on each individual hanger spreadsheet. The value specified on the Hanger Run Control Spreadsheet is used as the default for all hangers not having it defined explicitly.
A typical value to be used is 0.1 in.
Important: In some cases a Single directional restraint should be inserted instead of a rigid rod. Rigid rods are double acting restraints which can in some cases develop large “hold down” forces that don’t really exist because the support has lifted off, or because the rigid rod has bowed slightly. When this condition develops the user should rerun the hanger design inserting single directional restraints where rigid rods were put in by CAESAR II.
Hangers should probably never be replaced by rigid rods in very stiff parts of the piping system that are usually associated with rotating equipment or vessel nozzles that need to be protected.
Maximum Allowed Travel Limit
To specify a limit on the amount of travel a variable support hanger may undergo, specify the limit in this field. The
specification of a maximum travel limit will cause CAESAR II to select a constant effort support if the design operating travel exceeds this limit, even though a variable support from the manufacturer table would have been satisfactory in every other respect.
Constant effort hangers can be designed by inputting a very small number for the Maximum Allowed Travel Limit. A value of 0.001 is typical to force CAESAR II to select a constant effort support for a particular location.
Hanger Table
The following spring tables are currently included in CAESAR II:
1. Anvil 2. Bergen Power 3. Power Piping 4. NPS Industries 5. Lisega 6. Fronek 7. Piping Technology 8. Capitol 9. Piping Services 10. Basic Engineers 11. Inoflex 12. E. Myatt 13. SINOPEC 14. BHEL
15. Flexider 16. Carpenter & Paterson 17. Pipe Supports Ltd. 18. Witzenmann 19. Sarathi 20. Myricks
21. China Power 22. Pipe Supports USA 23. Quality Pipe Supports 24. PiHASA
25. Binder 26. Gradior 27. NHK
Additional design options are invoked by further use of the following checkboxes.
Extended Range Cold Load Design
Hot load centered (if possible)
For example, to use Grinnell Springs and cold load design the user would check the "cold load design" checkbox.
To use Grinnell “Extended Range” springs, Cold Load Design, and to get the Design Hot load centered in the middle of the hanger table, if possible, the user would check all three checkboxes.
A single job can use any combination of tables. The hanger table can be specified on the individual hanger spreadsheet, or can be specified on the Hanger Run Control Spreadsheet (see "Hanger Data" on page 3-114).
If a spring table is entered in the Hanger Design Control Spreadsheet then it is used as the default for all subsequent hangers defined. The Hanger Design Control Spreadsheet defaults to the hanger table-specified in the configuration file.
The maximum load range was included in CAESAR II to permit the selection of less expensive variable support hangers in place of constant effort supports when the spring loads are just outside the manufacturers recommended range. Users should make sure that the maximum load range is available from the manufacturer as a standard item.
Extended Load Range Springs. Extended load ranges are the most extreme ranges on the spring load table. Some manufacturers build double spring supports to accommodate this range, and others adjust the top or bottom travel limits to accommodate either end of the extended table. Before using the maximum ranges, the user should make sure that the manufacturer can properly supply the spring. Use of the extended range often eliminates the need to go to a constant effort support. Lisega springs do not support the "extended range" idea. A request for extended Lisega springs results in the standard Lisega spring table and ranges.
Cold Load Spring Hanger Design. Cold Load Spring Hanger Design is a method of designing the springs, whereby the hot (or operating) load is supported in the cold (or installed) position of the piping. This method of spring design offers several advantages over the more usual hot load design:
Hanger stops are easier to remove.
There is no excessive movement from the neutral position when the system is cold or when the stops are removed.
Spring loads can be adjusted before the system is brought up to temperature.
Some feel that the cold load approach yields a much more dependable design.
In some system configurations, operating loads on connected equipment are lower. A typical configuration resulting in this “load-reduction” is one where a hot vertical riser, anchored at the bottom, turns horizontally into a nozzle
connection. The spring to be designed is at the elbow adjacent to the nozzle. Operating loads are lower because the difference between the hot and cold loads counters the moment produced by the vertical thermal expansion from the anchor.
The disadvantages to cold load design are
In some systems, in the hot condition the loads on rotating equipment may be increased by a value proportional to the spring rate times the travel.
Most installations are done on a hot load design basis.
The decision to use hot or cold load hanger design rests with the user.
Middle of the Table Hanger Design (Hot Load Centered). Many designers prefer that the hot load be centered as close as possible to the middle of the spring table. This is to provide as much “variability” either way before the spring bottoms out when the system is hot. This was a much more needed feature, before effective computer modeling of piping systems, when the weights at hangers were approximated by chart methods or calculated by hand. Activating this option does not guarantee that spring hot loads will be at the middle of the spring table, but CAESAR II makes every effort to move the hot load to this position. The CAESAR II design algorithm will go to a higher size spring if the design load is closer to the middle of the larger springs range, but will never switch spring types. This option can only result in a one size larger spring when it is effective. CAESAR II will attempt to move the hot load to the next higher spring when it is within 10% of the maximum travel range for the spring. If the new spring is not satisfactory then the old one will be used, even though its hot load is within 10% of the high end of the table load range, to get a spring's hot load close to the middle of the table.