Safetyo Make sure pipes are at least 7 ft. (2.1m.) above platforms or workingareas. Do not run pipes at very low levels (say less than 2ft. (0.6m.)above floors or platforms) even although these areas are notdesignated for operation or access-pipes below this level are a serioustrip hazard during maintenance or emergency operationso Position valves to leave at least 6 in. (0-15 m) clear space round handwheelso On hot or corrosive liquids, avoid joints at eye level or over platformsPage 40 of 48o Check relief valve or bursting disc discharge piping carefully with thedesigner. General points to note are:o Fit light weatherproof cover over exit to atmosphere to preventrainwater entering and settling in pockets or on relief devices. Thiscover must be of light construction to reduce its inertia-it must openquickly and with minimum pressure rise when a relieving deviceoperateso Provide small drain holes at lowest point of atmospheric dischargepipes. Note-Do not do this on flare systems or on sealed ventsystemso Discharge pipes entering a common main should make a 45lateral connection with the main as shown in Fig.14.34, to minimizeback pressure from main and to assist flow into the maino Check supports of discharge lines on relief valves from point ofview of weight of valve and reactions from sudden flow whendevice operates suddenlyo If screwed lines are used for flammable non-conductive fluids (e.g.hydrocarbon solvents), ensure that PTFE thread seal tape is not calledfor at screwed joints unless earthing connections are also made Maintenanceo Fit short spool pieces at nozzles of all equipment to facilitatedisconnection of piping during maintenance. Typical items where thisfeature is useful are Pumps, Compressors, Pulverizers and Crushers,Vessels with flanged lids, Centrifuges etc.o If short spool pieces are used at valves or control valve sets, ensurethat the spool is long enough to withdraw bolts easily on the spoolside-it is sometimes impossible to withdraw the bolts on the valve sideo Do not position flanges where spanner access to bolts is restricted bysteelwork, handrails etc.o The lowest point of any part of a pipe should be at least 6 in. (0.15 m.)above floor or platform level. Where a control valve is fitted in the pipe,increase this to 12 in. (0.3m.) to permit removal of bottom coverso Provide drain points on control valve sets handling dangerous fluids sothat the pocket of liquid between the block valve and the control valvecan be emptied safelyo Standardize steam trap sets as far as possible so that rapid repair byreplacement techniques can be used Constructiono Provide adequate (not excessive) site make-up points or closinglengthso Avoid, if possible, leaving site welds to be made in horizontal lines-onsuch welds the lower half must be made from below and is moredifficult for the weldero Ensure flange or thread ratings match throughout all pipes, particularlyat valves, control valves, and vessels. Valve flanges are sometimesmade to certain flange tables only. Cast-iron valves are almost alwaysPage 41 of 48flat faced; if raised face flanges are called for by the specification, thevalve mating flange must have the raised face machined off to matchthe valveo When pipes are carried over from one isometric to another, check thatthe break point is at an accessible location. Also ensure continuationnotes are shown on drawingso When starting new points at a tee from a main pipe, leave a stub about12 in. (300mm) long projecting from the main or use a welded tee sothat the pipes can be joined on site by a butt weld. Do not leaveerectors with the job of making difficult stub tee connections on siteo When small branches are needed on large pipes, provide gussetplates to reinforce the branch against damage during transport andconstructiono Provide temporary strainers in lines to remove construction debriso Check hot lines with designer to see if cold pull is called for-if so,specify location and amount on drawingo If expansion bellows are fitted in pipes, add note to remind erector toleave the protecting bracer rods in during construction and remove atstart-up13 PIPE SUPPORTSDuring the pipe layout stage, supports should be defined for use on the project.These may be company standard or makers standard types as found mosteconomic; the important point is that standards be selected. Standard assemblyand detail drawings with parts lists for each type should be available in a formatwhich leaves the pipe size to be supported and possible other features (e.g. lengthof hanger type support) to be specified separately. By this means, a relatively smallnumber of drawings can serve for a large number of supports. Each type of supportshould be given a short identifier, which may be based on manufacturers orcompanys standards or perhaps identified specially for the project.Support positions and types should be selected, as the piping layouts are beingfinalized and completed. To avoid complication, it is not usual to indicate thesupports on the pipe layout drawings, but a progressive recording of positionsshould be done on separate transparencies or on the piping isometrics.Dimensional positioning of type and recording of all supports are important,particularly so if hot pipes subject to expansion are concerned. In this case, ahanger placed a matter of inches out of position can cause stresses, which may splita pipeline during test or at start-up. There is also the question of pipe deflectionleading to overstressing and pipe logging if a support is not placed in accordancewith its calculated position.A plan of supports need only be a simple type of drawing provided that locationdimensions are incorporated. There is no need to indicate supports in detail a smallcircle plus the support schedule number is all that is required.Page 42 of 48Supporting of pipes should follow the general sequence of layout of piping. This willensure that important and large pipes are attended to first. A support scheduleshould be drawn up as the job proceeds to identify types and sizes record andprovide a progressive checklist of detailing, fabrication, and erection work. Varioustypes of pipe supports are shown in FIG.8. Function of the system support:The mechanical requirements of the piping support system are: To carry the weight of the piping filled with water (or other liquid involved) andinsulation if used, with an ample safety margin use a factor of three (= ratioof the load just causing failure of support or hanger to actual load) or thesafety factor specified for the project. External loading factors to beconsidered are the wind loads, the probable weight of ice buildup in coldclimates, and seismic shocks in some areas To ensure that the material from which the pipe is made is not stressedbeyond a safe limit. In continuous run of the pipe, maximum tensile stressoccurs in the pipe cross section at the support. The system of supportsshould minimize the introduction of twisting forces in the piping due to offsetloads on the supports; the method of the cantilevered sections to substantiallyeliminate torsional forces To allow for draining, holdup of liquid can occur due to pipes saggingbetween supports. Complete draining is ensured by making adjacent supportadequately tilt the pipe To permit thermal expansion and contraction of the piping To withstand and dampen vibrational forces applied to the piping bycompressor, pump, etc.Ideally, each point of support would be at the centre of gravity of an associatedlength of piping, Carrying out this scheme thru the entire piping system wouldsubstantially relieve the system from twisting forces, and would be stressed onlyverticallyFollowing points should be to considered while supporting the pipes: Ideally, each point of the support would be at the centre of gravity of anassociated length of piping. Carrying this scheme through the entire pipingsystem would substantially relieve the system from twisting forces, andsupports would be stressed only vertically The presence of heavy flanges, valves, etc., in the piping will set the centre ofgravity away from the midpoint of the associated length The nature of the conveyed material, the process, and flow requirementsdetermines how much sagging can be accepted. Sagging is reduced bybringing adjacent points of support closer. Pocketing of liquid due to saggingcan be eliminated by sloping the line so that the difference in height betweenthe adjacent supports is at least equal to thrice the deflection (sag) at the mid-point, lines which require sloping include blow down headers, pressure relieflines, and some process, condensate and air linesPage 43 of 48 Sloped lines on pipe racks:Sloped lines can be carried on bracket attached to the pipe rack stanchions.To obtain the required change in elevation at each bend, the bracket may beattached at the required elevation and the slope obtained by using shoes ofdifferent sizes-this method leads to fewer construction problems. Shoes ofgraded sizes are also the best method for sloping smaller lines on the piperack. It is not usual or desirable to hang lines from the pipe rack unlessnecessary vertical clearances can be maintained. Sloped lines in buildings:Inside a building, both large and small sloped lines can rest on steel brackets,or to be held with hangers. Rods with turnbuckles are used for hangers onlines required to be sloped. Otherwise, drilled flats bar can be used. Supporting pipe made from plastics or glass:Pipes made either from flexible or rigid plastics cannot sustain the same spanloads as metal pipe, and requires a greater number of support points. Oneway to provide support is to lay the pipe upon length of steel channel sectionor half section of pipe, or suspending it from other steel pipes. The choice ofsteel section would depend on the span load size and type of plastic pipe. Design Points: General Design hangers for 2 and larger pipe to permit adjustment afterinstallation If piping is to be connected to equipment, a valve, etc., or piping assemblythat will require removal during maintenance, support the piping such thattemporary support are not needed Base load calculations for variable-spring and constant load supports onthe operating conditions of the piping (do not include the weight ofhydrostatic test fluid) If necessary, suspend pipes smaller than 2 nominal size from 4 andlarger Terms used in support SupportThe weight of piping is usually carried on supports made from structuralsteel, concrete or wood. HangerDevice, which suspends piping (usually a single line) from structural steel,concrete or wood. Hangers are usually adjustable for height. AnchorA rigid support, which prevents transmission of movement (thermal,vibratory, etc.) along piping. Construction may be from steel plate,brackets, flanges, rods, etc. Attachment of an anchor to pipe shouldpreferably encircle the pipe and be welded all around as this gives a betterdistribution of stress in the pipe wall. TiePage 44 of 48An arrangement of one or more rods, bars, etc. to restrain movement ofpiping. Dummy LegAn extension piece (of pipe or rolled steel section) welded to an elbow inorder to support the pipeline.The following hardware is used where mechanical and/or thermal movementis to be guided: GuideA means of allowing a pipe to move along its length, but not sideways. ShoeA metal piece attached to the underside of a pipe, which rests onsupporting steel. Primarily used to reduce wear from sliding for linessubject to movement. Permit insulation to be applied to the pipe. SaddleA welded attachment for pipe requiring insulation, and subject tolongitudinal or rolling movement (resulting from temperature changesother than climatic). Saddle may be used with guides. Slide PlateThe two plates used in a support are made from or faced with a materialof low frictional coefficient to reduce frictional resistance during movementof pipeline to with stand mechanical stress and temperature changes.Plates are often made from graphite blocks, steel plates with a Teflonfacing are available and may be welded to steel. Spring hangers or supportsAllow variations in the length of the pipe due to change in temperature,and often used for vertical lines.There are two types of spring hanger or support: Constant Load HangerThe device consists of a coil spring and lever mechanism in a housing.Movement of the piping, within limits, will not change the spring forceholding up the piping, thus, no additional forces will be introduced tothe piping system. Variable spring Hanger, and supportThese devices consist of a coil spring in a housing. The weight of thepiping rest on the spring in compression. The spring permits a limitedamount of thermal movement. A variable spring hanger holding up avertical line will reduce its lifting force as the line expands towards it.Both i.e. variable spring hanger and support place a load on the pipingsystem, where this is undesirable; a constant load hanger can be usedinstead. Hydraulic dampener, shock, snubber, or sway suppressorOne end of the unit is attached to piping and other to structural steel orconcrete. The unit expands or contracts to absorb slow movement of thepiping, but rigid to rapid movement.Page 45 of 48 Sway brace, or sway arrestorIt is essentially a helical spring in a housing, which is fitted, betweenpiping and a rigid structure. Its function is to buffer vibration and sway. Welding to pipeIf the applicable code permits, lugs may be welded to pipe for1. Fixing hangers to structural steel, etc.2. Attaching to pipe3. Supporting pipeWelding supports to prelined pipe will usually spoil the lining, andtherefore lugs etc. must be welded to the pipe and fittings before thelining/cladded insulation is applied. Welding of supports and lugs to thepipes and vessels to be stress relieved should be done before heattreatment.Various types of piping supportsRod Eyerod Clevis with rod Clevis with rod Spring hangerwith rodRod Turn buckle Spring hanger Clevis with rod Hanger with lugwith rod with eye rodFIG.8Page 46 of 48FIG.8 (CONT.)Clevis with pipe Clevis with pipe Channel with weld Welded bracketsand clampDummy leg Wye-type shoe Bent flat bar Dummy legT section Saddle with roller U bolt With Slide plates Steel rodSupporting Elbow Adjustable support Drip leg supportFIG.8Page 47 of 48FIG.8 (CONT.)With spring support Piping support assemblyFIG.8 Layout consideration to facilitate support:The two cardinal principles in routing lines for economic support, restraints, andbracing are: Group pipe lines so as to minimize the numbers of structures needed solelyfor pipe supports, restraints, or braces. Keep lines located close to possible points of supports, etc. either to grade orto structures, which are to be provided for other purposes. The significant general considerations affecting the routing of the pipingfor favourable support may be summarized as follows:1. The piping system should be self-supporting insofar as practicable andconsistent with flexibility requirements.2. Excess flexibility may make additional supports or restraints necessary toavoid movement and vibration in such amplitude as to arouse personnelapprehension. This situation is apt to occur on vertical lines where only onepoint of support is needed to sustain the weight.3. Free movement expansion joint systems involving appreciable unbalancedthrusts from pressure should be avoided unless such forces can be taken canbe taken on substantial structure, or at grade.4. Piping prone to vibrate, such as compressor suction or discharge and driverexhaust lines, should be routed for support independent from other piping andlightly braced structures and buildings. Routing should permit the use ofresting or similar supports offering resistance to motion and providing samedamping capacity, rather than hanging supports.5. The pipeline should be sufficient close to the point of support or restraint sothat the structural connection can have adequate rigidity and details can besimple and economical.