A pipe support or pipe hanger is a designed element that transfer the load from a pipe to the supporting structures. The load includes the weight of the pipe proper, the content that the pipe carries, all the pipe fittings attached to pipe, and the pipe covering such as insulation. The four main functions of a pipe support are to anchor, guide, absorb shock, and support a specified load. Pipe supports used in high or low temperature applications may contain insulation materials. The overall design configuration of a pipe support assembly is dependent on the loading and operating conditions.
Loads on piping system
Primary load These are typically steady or sustained types of loads such as internal fluid pressure, external pressure, gravitational forces acting on the pipe such as weight of pipe and fluid, forces due to relief or blow down, pressure waves generated due to water/steam hammer effects.
Sustained loads Internal/External Pressure: A pipe used for transporting fluid would be under internal pressure load. A pipe such as a jacketed pipe core or tubes in a Shell & Tube ex-changer etc. may be under net external pressure. Internal or external pressure induces stresses in the axial as well as circumferential (Cylinder stress Hoop Stress) directions. The pressure also induces stresses in the radial direction, but these are often neglected. The internal pressure exerts an axial force equal to pressure times the internal cross section of the pipe. F =P[πd^2/4]. If outer diameter is used for calculating approximate metal cross-section as Pressure well as pipe cross-section, the axial stress can often be approximated as follows : S =Pd /(4t) Dead weight: It is the self weight of pipe including fluid, weight of Piping and plumbing fittings & other inline components (say valve, Thermal insulation insulation etc.). This type of loads act throughout the life cycle of pipe. In horizontal pipes, these loads cause bending, and the bending moment is related to Stress (mechanics)#Simple stresses normal and shear stresses. Pipe bending is caused mainly due to two reasons: distributed weight load (e.g. fluid weight) and concentrated weight load (e.g. valve weight). The weight of risers (vertical sections of pipe) can be supported by riser clamps.
Occasional loads Wind load: Piping which are located outdoors and thus exposed to wind will be designed to withstand the maximum wind velocity expected during the plant operating life. Wind force is modelled as a uniform load acting upon the projected length of the pipe perpendicular to the direction of the wind. Wind pressure for various elevations will be used to calculate wind force using the following formula. Fw = Pw x S x A, where Fw = The total wind force, Pw = The equivalent wind pressure, S = Wind Drag coefficient shape factor, A = Pipe exposed area. Seismic load: Seismic loading Seismic load is one of the basic concepts of earthquake engineering which means application of an earthquake-generated agitation to a structure. It happens at contact surfaces of a structure either with the ground,[2] or with adjacent structures,[3] or with gravity waves from tsunami. Water hammer: Water hammer (or more generally, fluid hammer) is a pressure surge or wave caused when a fluid (usually a liquid but sometimes also a gas) in motion is forced to stop or change direction suddenly (momentum change). Water hammer commonly occurs when a valve closes suddenly at an end of a pipeline system, and a pressure wave propagates in the pipe. It's also called Water hammer hydraulic shock. Steam hammer: Steam hammer, the pressure surge generated by transient flow of super-heated or saturated steam in a steam-line due to sudden stop valve closures is considered as an occasional load. Though the flow is transient, for the purpose of piping stress analysis, only the unbalanced force along the pipe segment tending to induce piping vibration is calculated and applied on the piping model as static equivalent force. Safety valve Discharge: Reaction forces from relief valve discharge is considered as an occasional load. The reaction force due to steady state flow following the opening of safety relief valve in an open discharge installation can be calculated in accordance with ASME B31.1 Appendix II and applied on the piping model as static equivalent force.
Secondary load Just as the primary loads have their origin in some force, secondary loads are caused by displacement of some kind. For example, the pipe connected to a storage tank may be under load if the tank nozzle to which it is connected moves down due to tank settlement. Similarly, pipe connected to a vessel is pulled upwards because the vessel nozzle moves up due to vessel expansion. Also, a pipe may vibrate due to vibrations in the rotating equipment it is attached to. Displacement loads:
Load due to thermal expansion of pipe Load due to thermal movement of equipment A pipe may experience expansion or contraction once it is subjected to temperatures higher or lower respectively as compared to temperature at which it was assembled. The secondary loads are often cyclic but not always. For example, load due to tank settlement is not cyclic. The load due to vessel nozzle movement during operation is cyclic because the displacement is withdrawn during shut-down and resurfaces again after fresh start-up. A pipe subjected to a cycle of hot and cold fluid similarly undergoes cyclic loads and deformation.
Types of pipe supports
Rigid support Rigid supports are used to restrict pipe in certain direction(s) without any flexibility (in that direction). Main function of a rigid support can be Anchor, Rest, Guide or both Rest & Guide.
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