For the proper working of the piping system, it has to be supported properly. The major purpose of pipe support is described below:
Piping Supports for Carrying Weights
Pipe Supports are required to support the line during all conditions i.e. during operation as well as during testing. In the case of the vapor line, this difference will be very large due to hydro testing. Supports should be designed for this load (unless otherwise decided in the project). Sometimes the line is capable of having longer span but load coming on the support may be very large (especially with large diameter pipelines). Then to distribute the load uniformly, the number of supports should be provided with a smaller span. Note: 1. it may be noted that during testing conditions there is no thermal load. 2. All spring supports are locked during testing.
Piping Supports to Take the ‘Thermal or Expansion Load’
Whenever thermal expansion is restricted by pipe supports, it introduces additional load on the support. Support restraints must be designed to take this load in addition to all other loads.
Pipe Supports transfer the Occasional Earth Quake Loads
The earthquake is normally associated with horizontal acceleration of the order of 1 to 3 m/sec2. This is around 10% to 30% of the gravitational acceleration and introduces a horizontal force of about 10 to 30% of the vertical load (or supported mass). While designing pipe support, this should be taken care of.
Take ‘Hydraulic Thrust in Piping’
The hydraulic thrust (Fig. 1) in the pipeline is present at certain points such as pressure reducing valve, relief valve, bellows, etc.
If the control valve has large pressure differential and the line size is more, then this force can be very high.
The support should be provided and designed to take this load, otherwise, this will load the piping system and may cause failure.
Piping supports absorb ‘Vibration of Piping System’
When the pipe is subjected to moving machinery or pulsating flow or very high-velocity flow, the pipe may start vibrating vigorously and ultimately may fail, particularly if the span is large. To avoid this it may be required to introduce additional supports at a smaller span apart from other requirements. It may not take axial load but must control lateral movements.
Carry the ‘Occasional Wind Load’:
Wind introduces lateral load on the line. This load is considerable especially on large diameter pipes and increases as line size is increased. This load tends to sway the line from its normal position and line must be guided properly against it to avoid any kind of malfunction. In case of large diameter overhead lines, supported by tall support extended from the floor, wind load introduces large bending moments and should be considered critically.
Support the System during ‘Transient Period of Plant & Standby’
Transient Condition: Transient condition refers to the start-up or shutdown condition in which one equipment may get heated up faster and the other one gets heated slower. Due to this the expansion of one equipment which in normal operation will get nullified, may not get nullified and exert a thermal load on supports.
The standby condition is also similar. If there are two pumps, one being standby and both connected in parallel (as shown), the design and operating temperature of both the connections will be the same. But the expansion of two parallel legs will not be nullified because at a time only one leg will be hot and another being cold.
Piping Supports for ‘Noise Control’
In most of the plants, noise is resulting from vibration and if such vibrations are controlled, noise is reduced to a great extent. In such lines, between clamp (i.e. support) and pipe, the asbestos cloth is put to absorb vibration and avoid noise.
Noise due to pulsating flow can be reduced by using a silencer in the line. Still, if it is not below an acceptable level acoustic enclosure may be used. Insulation over line also helps in reducing the noise.
Support the System during ‘Maintenance Conditions’
When for maintenance certain equipment or component like valve is taken out, remaining system should not be left out unsupported.
Referring to the FIG-3, support ‘S1’ will be sufficient but when valve ‘V1’ is taken out for maintenance there will not be any support for the vertical leg. Therefore second support ‘S2’ may be required to take care of such conditions.
Piping Support for ‘Shutdown Conditions’
In shutdown condition, all equipment may not be in the same condition as in operating condition. For example, refer the pump discharge line in FIG-4, Point A is resting, Point B & C are spring supports and Point D is the pump discharge nozzle. The springs are, designed based on weights considering the weight of fluid as well as pipeline and thermal movements. But during shutdown conditions, the fluid may be drained and the pipe becomes lighter. Hence the spring will give an upward reaction and shall load the nozzle ‘D’ beyond the permissible limit.
In this case, a limit stop is used which will not allow Point C to move up above the horizontal level. (However, it will allow downward movement during operating condition).
Use of Pipe Support for Erection Conditions
Erection condition can be different than the operating condition which should be considered while designing supports.
For example, for normal operation, a long vessel supported by three supports, S1, S2 & S3 is shown in FIG-5. If support S2 is higher than all load will act at S2 only. During an erection, if the level of S2 is lower than the entire load will be divided into two supports S1, S2 only. Therefore the foundation of S1, S2 & S3 should be capable of taking such conditions.
A pipeline supported by S1, S2 & S3 taken from the vessel is shown in above FIG – 6. During operation, there will be no weight at S2 & S3 (as it is the only guide), but wind condition will be there. Loads due to such conditions must be considered while designing the supports.
Reduce Vibration Amplitudes
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