piping support spacing – What Is Piping

Piping support plays a very crucial role in the proper functioning of the piping systems. Pipe support carries the pipe weight with contents. To maintain the integrity of the piping system, A pipe must be supported following a proper span. Pipe support engineering is very critical for the success of any project as an accurate and judicious selection of piping support is required. Pipes as irregular space frames are not self-supporting so must be supported. Piping Loads are transmitted from pipe to supporting structures with the help of pipe supports. Proper pipe support knowledge during the layout stage is advantageous. The piping system is a major part of any hydrocarbon industry. Proper pipe support knowledge during the layout stage is advantageous. Piping Loads generated due to Weight, Pressure, Temperature, or Occasional Event has to be transmitted from pipe to supporting structures with the help of appropriate pipe supports. Difference between Pipe Support and Pipe Restraint The term “Restraints” is invariably used for pipe supports. However, there is a little difference between pipe support and restraint. Pipe supports are used to support the piping system by carrying the vertical load whereas pipe restraints limit the movements of the pipe so take care of the horizontal loads. So from the definition, Simple Rest is pipe support but Guide and line stops are pipe restraints. Normally, All pipe restraints come in combination with piping supports. Pipe support and restraints combinedly can be said pipe support systems. Henceforth, the term pipe support refers to the pipe support system. Purpose or Functions of piping support The various functions that pipe support serves are as follows: To prevent Pipe stresses in excess to allowable.To eliminate the Leakages in joints.To absorb Excessive Line Vibrations.To counter the undesirable effects of Seismic, wind, water hammer, slug, and other dynamic loadings.To remove unintentional disengagement (lift-off) of piping from its supports.To prevent excessive pipe sag (Normally more than 10 mm for process piping and 2.5 mm for power piping; 12.5 mm for GRE/GRP piping)To eliminate exposure of elements to temperature extremes, outside their design limit.To limit undesirable line movements to protect sensitive equipment against overloading.To redirect pipe thermal movements to the favourable direction.to reduce excessive loading in support itself For the proper working of the piping system, it has to be supported properly. The major purpose of pipe supports can be elaborated as follows: 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 a longer span but the 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 a large pressure differential and the line size is more, then this force can be very high. Fig. 1: Figure showing thrust force 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 the line must be guided properly against it to avoid any kind of malfunction. In the 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. Fig. 2: Operating- Standby Condition 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 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 the valve is taken out, the remaining system should not be left out unsupported. Fig. 3: Figure showing support addition during maintenance activities 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 conditions, all equipment may not be in the same condition as in operating conditions. For example, refer to 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. Fig. 4: Use of Limit elements in spring during shut down 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 conditions). Use of Pipe Support for Erection Conditions Erection conditions 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 then 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. Fig. 5: Vessel supported at three supports. 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 conditions will be there. Loads due to such conditions must be considered while designing the supports. Fig. 6: Pipe supported from vessel cleats. Codes and Standards for piping support Design The following codes and standards are used for piping support design. MSS-SP-58- Establishes the material, design, and inspection criteria to be used in the manufacturing of standard pipe supports. (USA)MSS-SP-69- Provides recommendations for the selection and application of pipe supports. (USA)MSS-SP-89- Provides recommendations for the fabrication and installation of pipe supports. (USA)BS-3974- Specification of pipe supports 1, 2, 3. (UK)VGB-R-510 L- Standard supports guidelines. (Germany)RCC-M- Specifications for pipe supports. (France)MITI 501- Technical regulations (Japan) Piping Support Design and Selection The complex requirement of today’s piping support design is reliable functioning, maintenance-free operation, economic and easy installations, quick delivery of components, and low unit prices. Major Criteria (Parameter) governing the pipe support hardware selection are Pipe Support function, Pipe Material of constructionThe magnitude of expected operational and occasional load, Available space limitations, Design temperature of the piping system, Expansion effects of the piping systems, The piping attachment and supporting structure material compatibility, Piping insulation/cladding, material, and thicknessSuitability to the environment, Ease of operation, inspection and installation. Piping Support Types Pipe Supports are categorized based on the following parameters Based on attachment with PipePrimary Piping SupportSecondary Piping SupportBased on Support hardware rigidityRigid supportResilient Support/ Elastic SupportAdjustable SupportBased on Piping InsulationPiping Supports for Hot InsulationPiping Supports of Cold InsulationPiping Supports for Acoustic InsulationBased on WeldingWelded Pipe SupportClamped Pipe SupportBased on Pipe Support functionResting SupportGuide SupportAxial Stop or Line StopAnchor Support Primary Piping Support Pipe Supports that are directly attached to the pipe are called Primary pipe Supports. For example, Shoe support, Clamp Support, Guide Support, Line Stop Support, Trunnion Support, etc. The design and selection of primary pipe support (Fig. 1) is the responsibility of the piping team. Secondary Piping Support Pipe supports that are not directly attached to the pipe are called secondary piping supports. Support Brackets, Secondary Steel members on which pipe or primary supports rest, Tee Post, Goal Post, sleepers, racks, etc are examples of secondary pipe supports. The design and selection of secondary pipe supports (Fig. 7) are the responsibility of the civil team. Fig. 7: Primary vs Secondary Support Piping Support guide for Optimization The following points need to be followed for optimized pipe supporting. Group pipelines so as to minimize the number of structures needed solely to pipe supports.Route lines close to the possible point of supports ( i.e. grade or structure which is provided for other purposes.)Supports or braces to be located at or near neutral pts. (thermal null pts)Supports to be located as near as possible to concentrated loads such as valves, flanges, heavy actuators, etc.Piping susceptible to vibration such as compressor connected lines to be supported independently. The use of hold down or similar supports offering resistance to motion and providing some damping capacity to be used rather than hanging type supports.Piping connected to the top of the vessel to be advantageously supported from the vessel to minimize relative movement between supports and piping.Always maintain the distance between supports as per project specification recommended support span table. ( it is applicable to straight run pipe length only.) When a change of direction in a horizontal plane occurs, it is suggested that the spacing be limited to ¾ times the standard pipe span.Sufficient space to be provided to facilitate support assembly installation, inspection, and maintenance. Fig. 8: Typical Piping Supports in Operating Plant Piping support terminologies and definitions Brace or Bracing Support- A device primarily intended to resist displacement of piping due to forces other than thermal expansion and gravity. Anchor Support or Fixed Support- A rigid restraint providing substantially full fixation is termed as an anchor. Anchor support restricts all six degrees of freedom and does not allow the pipe to move in any direction. Normally Full Welded or Bolted supports are called anchor supports. Full Anchor supports (Fig. 10) are rarely used in piping systems. Stop- A device that permits rotation but prevents translatory movements of piping. A line stop or axial stop (Fig. 9) prevents pipe movement in the axial direction of the pipe. It is also known as a stopper. Guide- A device that prevents the rotation of one or more axis is called a guide (Fig. 10). Guide supports (Fig. 8) prevents Lateral pipe movements. Hold Down Support- A device that holds the pipe in position disallowing vertical upwards movement or allows decided upward movement. Hold down supports prevent pipe dis-engagement from the Support structure. Hanger- A support by which piping is suspended from a structure that functions by carrying the piping load in tension. Resilient support- A support that includes one or more largely elastic members to carry pipe sustain + thermal loads at the same time allowing pipe thermal movement in the desired direction. Rest Support or Sliding support- A device that is provided below piping to take gravity loads, offering no resistance other than frictional to horizontal motion. Rest supports (Fig. 8) do not allow the pipe to sag or move downward. Rigid support- A support providing stiffness in at least one direction. Damping element- A device that increases damping of a system offering high resistance against rapid displacement, caused by dynamic loading while permitting essentially free movement. Adjustable Support- An adjustable support (Fig. 9) can be adjusted at the site during plant operation. These supports are normally provided for pipe and equipment alignment purposes. Dummy Leg - Basically an extension pipe welded to an elbow, to provide support either as a resting, anchor, etc. Fig. 9: Line Stop and Adjustable Trunnion Support Types of Piping Supports The following types of piping supports are most popular in the oil and gas, petrochemical industry. Hanger Supports – 1) Variable Hanger 2) Constant Hanger 3) Rigid Hanger. Click here to know more about Spring hangers.Dynamically Loaded Supports – 1) Struts 2) Snubbers 3) Sway Brace 4) Energy absorbers 5) Pipe Clamps 6) Pipe whip / Hold down restraints.Pipe Bearing Components – 1) Pipe Saddle 2) Pipe Shoe 3) Pipe Trunnion 4) Wear Pad.Threaded Members – 1) welding nut 2) welded beam attachment 3) Clevis 4) Turnbuckle 5) Tie rod 6) Stud bolt, nut, locknut, spring washers, etc.Slide Bearing Plates – Teflon, Stainless steel, graphite. Fig. 10: Anchor Support and Shoe Support with Guide Pipe Support Manufacturers The number of Piping Support manufacturers is quite long. However, the following are the most popular: Piping Technology and Products Ltd.Carpenter and Paterson Ltd.Lisega Ltd.Binder Group Ltd.Pipe Support Group Ltd.Sarathi Engg Ent Pvt Ltd.Anvil Group etc to name a few Piping Support Engineering Minimum Data required to start supporting Piping GADElectrical and Inst cable trench/trays layoutsCivil and Structural drawingsPiping spec and line listInsulation specValve’s weightsEquipment connection displacementsStress recommendations (Stress isometrics) and Support loads. Pipe Support Span Typically piping is supported at regular intervals on steel supports embedded in concrete foundation or directly on the steel structure. The distance between supports is the supporting span. The basis for the calculation of maximum support span There are three main factors that affect the support span. StressDeflection/ sagging andFrequency of piping system (for two-phase flow lines, reciprocating equipment connected lines, vibrating lines, etc.). Click here to know more about pipe support span Piping Support Rules Supporting of Stress Critical Lines Criteria for critical linesSupport location by DesignersSupport type by stress engineerPrimary attachments and secondary supports by designersLine stop/Guide gaps to be taken care Supporting of non-critical lines Senior designer to decide support type Support span Guide span Concentrated loads e.g. valves, inst Long piping leg, stress engineer to be consulted Supporting of Insulated Pipes No direct resting, pipe shoe to be providedMinimum clearance between the insulation and the supporting structure shall be at least 50 mm. Supporting of Non- Insulated Pipes Directly rested except following Pipes with sizes larger than DN 600CS pipes with less than SCH 20SS pipes with less than SCH 10SThe pipe that requires a slopeDissimilar material to avoid galvanic corrosionPipe to be supported on pipe shoe to avoid damaging to the pipe wall Vertical piping support For vertical piping support, the below-mentioned guidelines are followed Standard piping support span chart does not apply Supports to be located on the upper half of the portion (i.e. above C.G. of pipe) The vertical guide spacing is normally lower than horizontal guide spacing Clamped supports with weld-on shear lugs to avoid the pipe slipping under the clamp Special Pipe Supports or SPS The pipe supports that do not fall in the above category are called special pipe supports. Various kinds of special pipes are required for critical lines. The design is normally slightly complicated and a separate drawing is prepared for each special pipe supports. For example Spring hanger along with GuideHanger along with guide and line stopNormal primary support requiring additional strengthening due to increased load, etc The drawing is normally prepared by the pipe stress or pipe support engineer and checked by a civil engineer to ascertain the structural member load-carrying capability. Video Tutorial on Pipe Supports The following video tutorial can be referred to for a basic understanding of the pipe supports https://www.youtube.com/watch?v=oHRAQRI6Cl4 Few more Resources for You… An article on Piping Support span Supporting of Dual Insulated Piping System Dynamic Restraints Piping Stress Analysis